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• MVVM- Expose Model object in ViewModel

  - by Angel

  I have a wpf MVVM application , I exposed my model object into my viewModel by creating an instance of Model class (which cause dependency) into ViewModel , and instead of creating seperate VM properties , I wrap the Model properties inside my ViewModel Property. My model is just an entity framework generated proxy classes. Here is my Model class : public partial class TblProduct { public TblProduct() { this.TblPurchaseDetails = new HashSet<TblPurchaseDetail>(); this.TblPurchaseOrderDetails = new HashSet<TblPurchaseOrderDetail>(); this.TblSalesInvoiceDetails = new HashSet<TblSalesInvoiceDetail>(); this.TblSalesOrderDetails = new HashSet<TblSalesOrderDetail>(); } public int ProductId { get; set; } public string ProductCode { get; set; } public string ProductName { get; set; } public int CategoryId { get; set; } public string Color { get; set; } public Nullable<decimal> PurchaseRate { get; set; } public Nullable<decimal> SalesRate { get; set; } public string ImagePath { get; set; } public bool IsActive { get; set; } public virtual TblCompany TblCompany { get; set; } public virtual TblProductCategory TblProductCategory { get; set; } public virtual TblUser TblUser { get; set; } public virtual ICollection<TblPurchaseDetail> TblPurchaseDetails { get; set; } public virtual ICollection<TblPurchaseOrderDetail> TblPurchaseOrderDetails { get; set; } public virtual ICollection<TblSalesInvoiceDetail> TblSalesInvoiceDetails { get; set; } public virtual ICollection<TblSalesOrderDetail> TblSalesOrderDetails { get; set; } } Here is my ViewModel , public class ProductViewModel : WorkspaceViewModel { #region Constructor public ProductViewModel() { StartApp(); } #endregion //Constructor #region Properties private IProductDataService _dataService; public IProductDataService DataService { get { if (_dataService == null) { if (IsInDesignMode) { _dataService = new ProductDataServiceMock(); } else { _dataService = new ProductDataService(); } } return _dataService; } } //Get and set Model object private TblProduct _product; public TblProduct Product { get { return _product ?? (_product = new TblProduct()); } set { _product = value; } } #region Public Properties public int ProductId { get { return Product.ProductId; } set { if (Product.ProductId == value) { return; } Product.ProductId = value; RaisePropertyChanged("ProductId"); } } public string ProductName { get { return Product.ProductName; } set { if (Product.ProductName == value) { return; } Product.ProductName = value; RaisePropertyChanged(() => ProductName); } } private ObservableCollection<TblProduct> _productRecords; public ObservableCollection<TblProduct> ProductRecords { get { return _productRecords; } set { _productRecords = value; RaisePropertyChanged("ProductRecords"); } } //Selected Product private TblProduct _selectedProduct; public TblProduct SelectedProduct { get { return _selectedProduct; } set { _selectedProduct = value; if (_selectedProduct != null) { this.ProductId = _selectedProduct.ProductId; this.ProductCode = _selectedProduct.ProductCode; } RaisePropertyChanged("SelectedProduct"); } } #endregion //Public Properties #endregion // Properties #region Commands private ICommand _newCommand; public ICommand NewCommand { get { if (_newCommand == null) { _newCommand = new RelayCommand(() => ResetAll()); } return _newCommand; } } private ICommand _saveCommand; public ICommand SaveCommand { get { if (_saveCommand == null) { _saveCommand = new RelayCommand(() => Save()); } return _saveCommand; } } private ICommand _deleteCommand; public ICommand DeleteCommand { get { if (_deleteCommand == null) { _deleteCommand = new RelayCommand(() => Delete()); } return _deleteCommand; } } #endregion //Commands #region Methods private void StartApp() { LoadProductCollection(); } private void LoadProductCollection() { var q = DataService.GetAllProducts(); this.ProductRecords = new ObservableCollection<TblProduct>(q); } private void Save() { if (SelectedOperateMode == OperateModeEnum.OperateMode.New) { //Pass the Model object into Dataservice for save DataService.SaveProduct(this.Product); } else if (SelectedOperateMode == OperateModeEnum.OperateMode.Edit) { //Pass the Model object into Dataservice for Update DataService.UpdateProduct(this.Product); } ResetAll(); LoadProductCollection(); } #endregion //Methods } Here is my Service class: class ProductDataService:IProductDataService { /// <summary> /// Context object of Entity Framework model /// </summary> private MaizeEntities Context { get; set; } public ProductDataService() { Context = new MaizeEntities(); } public IEnumerable<TblProduct> GetAllProducts() { using(var context=new R_MaizeEntities()) { var q = from p in context.TblProducts where p.IsDel == false select p; return new ObservableCollection<TblProduct>(q); } } public void SaveProduct(TblProduct _product) { using(var context=new R_MaizeEntities()) { _product.LastModUserId = GlobalObjects.LoggedUserID; _product.LastModDttm = DateTime.Now; _product.CompanyId = GlobalObjects.CompanyID; context.TblProducts.Add(_product); context.SaveChanges(); } } public void UpdateProduct(TblProduct _product) { using (var context = new R_MaizeEntities()) { context.TblProducts.Attach(_product); context.Entry(_product).State = EntityState.Modified; _product.LastModUserId = GlobalObjects.LoggedUserID; _product.LastModDttm = DateTime.Now; _product.CompanyId = GlobalObjects.CompanyID; context.SaveChanges(); } } public void DeleteProduct(int _productId) { using (var context = new R_MaizeEntities()) { var product = (from c in context.TblProducts where c.ProductId == _productId select c).First(); product.LastModUserId = GlobalObjects.LoggedUserID; product.LastModDttm = DateTime.Now; product.IsDel = true; context.SaveChanges(); } } } I exposed my model object in my viewModel by creating an instance of it using new keyword, also I instantiated my DataService class in VM, I know this will cause a strong dependency. So , 1- Whats the best way to expose Model object in ViewModel ? 2- Whats the best way to use DataService in VM ?

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• WPF - Bind Menu Item

  - by Miguel

  Hello, I am creating a menu and binding the menu items ate runtime as follows but I am not able to make it work. I am creating the menu as follows: Menu menu = new Menu(); menu.Items.Add(new MenuItem { Command = new PackCommand(), Header = "Pack" }); DockPanel.SetDock(menu, Dock.Top); content.Children.Add(menu); And I am implementing ICommand: public static class PackCommand : ICommand { Boolean CanExecute(object parameter) { return true; } void Execute(object parameter) { Packer packer = new Packer(); packer.Run(); } } I am not sure how to bind the menu item. Why CanExecute? Shouldn't it always? I only want to run packer.Run when the buttom is clicked. I think I should implement ICommand but I am not even sure I should do this? Could someone please help me out? Thanks, Miguel

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• Does the Microsoft SQL Server native client support IDBAsynchNotify?

  - by Aaron Klotz

  I'm working on some OLE DB code that runs queries on MS SQL Server via ICommand::Execute. I'm converting this code to operate asynchronously by setting the DBPROPVAL_ASYNCH_INITIALIZE property on the command before executing. I'd prefer to register a IDBAsynchNotify sink so that my code can be notified of events, as opposed to polling or blocking via ISSAsynchStatus. The documentation for ICommand::Execute does not show IConnectionPointContainer as an acceptable riid parameter, but the same document, when discussing the DB_S_ASYNCHRONOUS return code, suggests that it is possible to request an IConnectionPointContainer interface that I could use to register my event sink. When I call ICommand::Execute, passing IID_IConnectionPointContainer as the riid parameter, I receive the E_NOINTERFACE error. I also tried setting the DBPROP_IConnectionPointContainer property before Execute but I received the same results. If I have to, I'll use ISSAsynchStatus, but I'd much rather use IDBAsynchNotify. Is it possible?

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• Silverlight Cream for June 19, 2011 -- #1109

  - by Dave Campbell

  In this Issue: Kunal Chowdhury(-2-), Oren Gal, Rudi Grobler, Stephen Price, Erno de Weerd, Joost van Schaik, WindowsPhoneGeek, Andrea Boschin, and Vikram Pendse. Above the Fold: Silverlight: "Multiple Page Printing in Silverlight4 - Part 3 - Printing Driving Directions" Oren Gal WP7: "Prototyping Windows Phone 7 Applications using SketchFlow" Vikram Pendse Shoutouts: Not Silverlight, but darned cool... Michael Crump has just what you need to get going with Kinect: The busy developers guide to the Kinect SDK Beta Rudi Grobler replies to a few questions about how he gets great WP7 screenshots: Screenshot Tools for WP7 From SilverlightCream.com: Windows Phone 7 (Mango) Tutorial - 14 - Detecting Network Information of the Device Squeaking in just under the posting wire with 2 more WP7.1 posts is Kunal Chowdhury ... first up is this one on grabbing the mobile operator and othe rnetwork info in WP7.1 Windows Phone 7 (Mango) Tutorial - 15 - Detecting Device Information Kunal Chowdhury's latest is on using the DeviceStatus class in WP7.1 to detect device information such as is there is a physical keyboard installed, Memory Usage, Total Memory, etc. Multiple Page Printing in Silverlight4 - Part 3 - Printing Driving Directions Oren Gal has the final episode in his Multiple Page Printing Tutorial Trilogy up... and this is *way* cool... Printing the driving directions. AgFx hidden gem - PhoneApplicationFrameEx Rudi Grobler continues his previous post about AgFX with this one talking about the PhoneApplicationFrameEx class inside AgFx.Controls.Phone.dll.. a RootFrame replacement. Binding to ActualHeight or ActualWidth Stephen Price's latest XAML snippet is about Binding to ActualHeight or ActualWidth... you've probably tried to without luck... check out the workaround. Windows Phone 7: Drawing graphics for your application with Inkscape – Part I: Tiles Erno de Weerd decided to try the 'free' route to Drawing graphics for his WP7 app, and has part 1 of a tutorial series on doing that with Inkscape. Mogade powered Live Tile high score service for Windows Phone 7 Joost van Schaik expounds on his "Catch 'em Birds" WP7 game in the Marketplace... specifically the online leaderboard using the services of Mogade. Building a Reusable ICommand implementation for Windows Phone Mango MVVM apps WindowsPhoneGeek's latest post is discussing the ICommand interface available in WP7.1, and he demontstrates how to implement a reusable ICommand Implementation and how to use it. A TCP Server with Reactive Extensions Andrea Boschin is back posting about Rx, and promises this post *will be* Silverlight related eventually :) First up though is a socket server using Rx. Prototyping Windows Phone 7 Applications using SketchFlow Vikram Pendse has a tutorial up for prototyping your WP7* apps in Sketchflow including a 5 minute video Stay in the 'Light! Twitter SilverlightNews | Twitter WynApse | WynApse.com | Tagged Posts | SilverlightCream Join me @ SilverlightCream | Phoenix Silverlight User Group Technorati Tags: Silverlight    Silverlight 3    Silverlight 4    Windows Phone MIX10

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• [Windows 8] An application bar toggle button

  - by Benjamin Roux

  To stay in the application bar stuff, here’s another useful control which enable to create an application bar button that can be toggled between two different contents/styles/commands (used to create a favorite/unfavorite or a play/pause button for example). namespace Indeed.Controls { public class AppBarToggleButton : Button { public bool IsChecked { get { return (bool)GetValue(IsCheckedProperty); } set { SetValue(IsCheckedProperty, value); } } public static readonly DependencyProperty IsCheckedProperty = DependencyProperty.Register("IsChecked", typeof(bool), typeof(AppBarToggleButton), new PropertyMetadata(false, (o, e) => (o as AppBarToggleButton).IsCheckedChanged())); public string CheckedContent { get { return (string)GetValue(CheckedContentProperty); } set { SetValue(CheckedContentProperty, value); } } public static readonly DependencyProperty CheckedContentProperty = DependencyProperty.Register("CheckedContent", typeof(string), typeof(AppBarToggleButton), null); public ICommand CheckedCommand { get { return (ICommand)GetValue(CheckedCommandProperty); } set { SetValue(CheckedCommandProperty, value); } } public static readonly DependencyProperty CheckedCommandProperty = DependencyProperty.Register("CheckedCommand", typeof(ICommand), typeof(AppBarToggleButton), null); public Style CheckedStyle { get { return (Style)GetValue(CheckedStyleProperty); } set { SetValue(CheckedStyleProperty, value); } } public static readonly DependencyProperty CheckedStyleProperty = DependencyProperty.Register("CheckedStyle", typeof(Style), typeof(AppBarToggleButton), null); public bool AutoToggle { get { return (bool)GetValue(AutoToggleProperty); } set { SetValue(AutoToggleProperty, value); } } public static readonly DependencyProperty AutoToggleProperty = DependencyProperty.Register("AutoToggle", typeof(bool), typeof(AppBarToggleButton), null); private object content; private ICommand command; private Style style; private void IsCheckedChanged() { if (IsChecked) { // backup the current content and command content = Content; command = Command; style = Style; if (CheckedStyle == null) Content = CheckedContent; else Style = CheckedStyle; Command = CheckedCommand; } else { if (CheckedStyle == null) Content = content; else Style = style; Command = command; } } protected override void OnTapped(Windows.UI.Xaml.Input.TappedRoutedEventArgs e) { base.OnTapped(e); if (AutoToggle) IsChecked = !IsChecked; } } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } To use it, it’s very simple. <ic:AppBarToggleButton Style="{StaticResource PlayAppBarButtonStyle}" CheckedStyle="{StaticResource PauseAppBarButtonStyle}" Command="{Binding Path=PlayCommand}" CheckedCommand="{Binding Path=PauseCommand}" IsChecked="{Binding Path=IsPlaying}" /> .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } When the IsPlaying property (in my ViewModel) is true the button becomes a Pause button, when it’s false it becomes a Play button. Warning: Just make sure that the IsChecked property is set in last in your control !! If you don’t use style you can alternatively use Content and CheckedContent. Furthermore you can set the AutoToggle to true if you don’t want to control is IsChecked property through binding. With this control and the AppBarPopupButton, you can now create awesome application bar for your apps ! Stay tuned for more awesome Windows 8 tricks !

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• CheckBox Command Behaviors for Silverlight MVVM Pattern

  - by Blake Blackwell

  I am trying to detect when an item is checked, and which item is checked in a ListBox using Silverlight 4 and the Prism framework. I found this example on creating behaviors, and tried to follow it but nothing is happening in the debugger. I have three questions: Why isn't my command executing? How do I determine which item was checked (i.e. pass a command parameter)? How do I debug this? (i.e. where can I put break points to begin stepping into this) Here is my code: View: <ListBox x:Name="MyListBox" ItemsSource="{Binding PanelItems, Mode=TwoWay}"> <ListBox.ItemTemplate> <DataTemplate> <StackPanel Orientation="Horizontal"> <CheckBox IsChecked="{Binding Enabled}" my:Checked.Command="{Binding Check}" /> <TextBlock x:Name="DisplayName" Text="{Binding DisplayName}"/> </StackPanel> </DataTemplate> </ListBox.ItemTemplate> </ListBox> ViewModel: public MainPageViewModel() { _panelItems.Add( new PanelItem { Enabled = true, DisplayName = "Test1" } ); Check = new DelegateCommand<object>( itemChecked ); } public void itemChecked( object o ) { //do some stuff } public DelegateCommand<object> Check { get; set; } Behavior Class public class CheckedBehavior : CommandBehaviorBase<CheckBox> { public CheckedBehavior( CheckBox element ) : base( element ) { element.Checked +=new RoutedEventHandler(element_Checked); } void element_Checked( object sender, RoutedEventArgs e ) { base.ExecuteCommand(); } } Command Class public static class Checked { public static ICommand GetCommand( DependencyObject obj ) { return (ICommand) obj.GetValue( CommandProperty ); } public static void SetCommand( DependencyObject obj, ICommand value ) { obj.SetValue( CommandProperty, value ); } public static readonly DependencyProperty CommandProperty = DependencyProperty.RegisterAttached( "Command", typeof( CheckBox ), typeof( Checked ), new PropertyMetadata( OnSetCommandCallback ) ); public static readonly DependencyProperty CheckedCommandBehaviorProperty = DependencyProperty.RegisterAttached( "CheckedCommandBehavior", typeof( CheckedBehavior ), typeof( Checked ), null ); private static void OnSetCommandCallback( DependencyObject dependencyObject, DependencyPropertyChangedEventArgs e ) { CheckBox element = dependencyObject as CheckBox; if( element != null ) { CheckedBehavior behavior = GetOrCreateBehavior( element ); behavior.Command = e.NewValue as ICommand; } } private static CheckedBehavior GetOrCreateBehavior( CheckBox element ) { CheckedBehavior behavior = element.GetValue( CheckedCommandBehaviorProperty ) as CheckedBehavior; if( behavior == null ) { behavior = new CheckedBehavior( element ); element.SetValue( CheckedCommandBehaviorProperty, behavior ); } return behavior; } public static CheckedBehavior GetCheckCommandBehavior( DependencyObject obj ) { return (CheckedBehavior) obj.GetValue( CheckedCommandBehaviorProperty ); } public static void SetCheckCommandBehavior( DependencyObject obj, CheckedBehavior value ) { obj.SetValue( CheckedCommandBehaviorProperty, value ); } } I used this article to get me started, but I'll readily admit this is over my head.

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• How do I attach commands to the checking and unchecking of a CheckBox?

  - by GraemeF

  In my ViewModel I have two commands: ICommand ExecuteMeOnCheck { get; } ICommand ExecuteMeOnUncheck { get; } I wish to attach these commands to a CheckBox and have one of them execute when it is checked and the other execute when it is unchecked. What's the best way to achieve this without cluttering the View with code-behind?

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• Get the value for a WPF binding

  - by Jose

  Ok, I didn't want a bunch of ICommands in my MVVM ViewModels so I decided to create a MarkupExtension for WPF that you feed it a string(the name of the method), and it gives you back an ICommand that executes the method. here's a snippet: public class MethodCall : MarkupExtension { public MethodCall(string methodName) { MethodName = methodName; CanExecute = "Can" + methodName; } public override object ProvideValue(IServiceProvider serviceProvider) { Binding bin= new Binding { Converter = new MethodConverter(MethodName,CanExecute) }; return bin.ProvideValue(serviceProvider); } } public class MethodConverter : IValueConverter { string MethodName; public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) { //Convert to ICommand ICommand cmd = ConvertToICommand(); if (cmd == null) Debug.WriteLine(string.Format("Could not bind to method 'MyMethod' on object",MethodName)); return cmd; } } It works great, except when the binding fails(e.g. you mistype). When you do this in xaml: {Binding MyPropertyName} you see in the output window whenever the binding fails. and it tells you the propertyName the Type name etc. The MethodConverter Class can tell you the name of the method that failed, but it can't tell you the source object type. Because the value will be null. I can't figure out how to store the source object type so for the following class public class MyClass { public void MyMethod() { } } and the following xaml: <Button Command={d:MethodCall MyMethod}>My Method</Button> It currently says: "Could not bind to method 'MyMethod' on object but I would like it to say: "Could not bind to method 'MyMethod' on object MyClass Any ideas?

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• Binding between Usercontrol with listbox and parent control (MVVM)

  - by walkor

  I have a UserControl which contains a listbox and few buttons. <UserControl x:Class="ItemControls.ListBoxControl" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"> <Grid> <ListBox:ExtendedListBox SelectionMode="Single" ItemsSource="{Binding LBItems}" Height="184"> <ListBox.ItemTemplate> <DataTemplate> <CheckBox Content="{Binding}"/> </DataTemplate> </ListBox.ItemTemplate> </ListBox> <Button Command="RemoveCommand"/> </Grid> </UserControl> And the code behind: public static readonly DependencyProperty RemoveCommandProperty = DependencyProperty.Register("RemoveCommand", typeof(ICommand), typeof(ListBoxControl), null); public ICommand RemoveCommand { get { return (ICommand)GetValue(RemoveCommandProperty); } set { SetValue(RemoveCommandProperty, value); } } public static readonly DependencyProperty LBItemsProperty = DependencyProperty.Register("LBItems", typeof(IEnumerable), typeof(ListBoxControl), null); public IEnumerable LBItems { get { return (IEnumerable)GetValue(LBItemsProperty); } set { SetValue(LBItemsProperty, value); } } I'm using this control in the view like this: <ItemControls:ListBoxControl Height="240" Width="350" LBItems="{Binding Items, Converter={StaticResource ItemsConverter}, Mode=TwoWay}" RemoveCommand="{Binding RemoveCommand}"/> The command works fine, though the listbox binding doesn't. My question is - WHY?

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• Predicate usually used for array/list how about here?

  - by amit kohan

  In following code (Josh Smith's article on MVVM), can somebody give me some insight about return _canExecute == null ? true : _canExecute(parameter); ? it is a normal if/else statement but I'm not getting the last part of it. public class RelayCommand : ICommand { #region Fields readonly Action<object> _execute; readonly Predicate<object> _canExecute; #endregion // Fields #region Constructors public RelayCommand(Action<object> execute) : this(execute, null) { } public RelayCommand(Action<object> execute, Predicate<object> canExecute) { if (execute == null) throw new ArgumentNullException("execute"); _execute = execute; _canExecute = canExecute; } #endregion // Constructors #region ICommand Members [DebuggerStepThrough] public bool CanExecute(object parameter) { return _canExecute == null ? true : _canExecute(parameter); } public event EventHandler CanExecuteChanged { add { CommandManager.RequerySuggested += value; } remove { CommandManager.RequerySuggested -= value; } } public void Execute(object parameter) { _execute(parameter); } #endregion // ICommand Members } Thanks.

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• Distinguishing between UI command & domain commands

  - by SonOfPirate

  I am building a WPF client application using the MVVM pattern that provides an interface on top of an existing set of business logic residing in a library which is shared with other applications. The business library followed a domain-driven architecture using CQRS to separate the read and write models (no event sourcing). The combination of technologies and patterns has brought up an interesting conundrum: The MVVM pattern uses the command pattern for handling user-interaction with the view models. .NET provides an ICommand interface which is implemented by most MVVM frameworks, like MVVM Light's RelayCommand and Prism's DelegateCommand. For example, the view model would expose a number of command objects as properties that are bound to the UI and respond when the user performs actions like clicking buttons. Many implementations of the CQRS use the command pattern to isolate and encapsulate individual behaviors. In my business library, we have implemented the write model as command / command-handler pairs. As such, when we want to do some work, such as create a new order, we 'issue' a command (CreateOrderCommand) which is routed to the command-handler responsible for executing the command. This is great, clearly explained in many sources and I am good with it. However, take this scenario: I have a ToolbarViewModel which exposes a CreateNewOrderCommand property. This ICommand object is bound to a button in the UI. When clicked, the UI command creates and issues a new CreateOrderCommand object to the domain which is handled by the CreateOrderCommandHandler. This is difficult to explain to other developers and I am finding myself getting tongue-tied because everything is a command. I'm sure I'm not the first developer to have patterns overlap like this where the naming/terminology also overlap. How have you approached distinguishing your commands used in the UI from those used in the domain? (Edit: I should mention that the business library is UI-agnostic, i.e. no UI technology-specific code exists, or will exists, in this library.)

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• How can I get started using TDD to code some simple functionality?

  - by Gabriel

  I basically have the gist of TDD. I'm sold that it's useful and I've got a reasonable command of the MSTEST framework. However, to date I have not been able to graduate to using it as a primary development method. Mostly, I use it as a surrogate for writing console apps as test drivers (my traditional approach). The most useful thing about it for me is the way it absorbs the role of regression testing. I have not yet built anything yet that specifically isolates various testable behaviors, which is another big part of the picture I know. So this question is to ask for pointers on what the first test(s) I might write for the following development task: I want to produce code that encapsulates task execution in the fashion of producer/consumer. I stopped and decided to write this question after I wrote this code (wondering if I could actually use TDD for real this time) Code: interface ITask { Guid TaskId { get; } bool IsComplete { get; } bool IsFailed { get; } bool IsRunning { get; } } interface ITaskContainer { Guid AddTask(ICommand action); } interface ICommand { string CommandName { get; } Dictionary<string, object> Parameters { get; } void Execute(); }

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• Semantic coupling vs. large class

  - by user106587

  I have hardware I communicate with via TCP. This hardware accepts ~40 different commands/requests with about 20 different responses. I've created a HardwareProxy class which has a TcpClient to send and receive data. I didn't like the idea of having 40 different methods to send the commands/requests, so I started down the path of having a single SendCommand method which takes an ICommand and returns an IResponse, this results in 40 different SpecificCommand classes. The problem is this requires semantic coupling, i.e. the method that invokes SendCommand receives an IResponse which it has to downcast to SpecificResponse, I use a future map which I believe ensures the appropriate SpecificResponse, but I get the impression this code smells. Besides the semantic coupling, ICommand and IResponse are essentially empty abstract classes (Marker Interfaces) and this seems suspicious to me. If I go with the 40 methods I don't think I have broken the single responisbility principle as the responsibility of the HardwareProxy class is to act as the hardware, which has all of these commands. This route is just ugly, plus I'd like to have Asynchronous versions, so there'd be about 80 methods. Is it better to bite the bullet and have a large class, accept the coupling and MarkerInterfaces for a smaller soultuion, or am I missing a better way? Thanks.

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• Silverlight Recruiting Application Part 5 - Jobs Module / View

  Now we starting getting into a more code-heavy portion of this series, thankfully though this means the groundwork is all set for the most part and after adding the modules we will have a complete application that can be provided with full source. The Jobs module will have two concerns- adding and maintaining jobs that can then be broadcast out to the website. How they are displayed on the site will be handled by our admin system (which will just poll from this common database), so we aren't too concerned with that, but rather with getting the information into the system and allowing the backend administration/HR users to keep things up to date. Since there is a fair bit of information that we want to display, we're going to move editing to a separate view so we can get all that information in an easy-to-use spot. With all the files created for this module, the project looks something like this: And now... on to the code. XAML for the Job Posting View All we really need for the Job Posting View is a RadGridView and a few buttons. This will let us both show off records and perform operations on the records without much hassle. That XAML is going to look something like this: 01.<Grid x:Name="LayoutRoot" 02.Background="White"> 03.<Grid.RowDefinitions> 04.<RowDefinition Height="30" /> 05.<RowDefinition /> 06.</Grid.RowDefinitions> 07.<StackPanel Orientation="Horizontal"> 08.<Button x:Name="xAddRecordButton" 09.Content="Add Job" 10.Width="120" 11.cal:Click.Command="{Binding AddRecord}" 12.telerik:StyleManager.Theme="Windows7" /> 13.<Button x:Name="xEditRecordButton" 14.Content="Edit Job" 15.Width="120" 16.cal:Click.Command="{Binding EditRecord}" 17.telerik:StyleManager.Theme="Windows7" /> 18.</StackPanel> 19.<telerikGrid:RadGridView x:Name="xJobsGrid" 20.Grid.Row="1" 21.IsReadOnly="True" 22.AutoGenerateColumns="False" 23.ColumnWidth="*" 24.RowDetailsVisibilityMode="VisibleWhenSelected" 25.ItemsSource="{Binding MyJobs}" 26.SelectedItem="{Binding SelectedJob, Mode=TwoWay}" 27.command:SelectedItemChangedEventClass.Command="{Binding SelectedItemChanged}"> 28.<telerikGrid:RadGridView.Columns> 29.<telerikGrid:GridViewDataColumn Header="Job Title" 30.DataMemberBinding="{Binding JobTitle}" 31.UniqueName="JobTitle" /> 32.<telerikGrid:GridViewDataColumn Header="Location" 33.DataMemberBinding="{Binding Location}" 34.UniqueName="Location" /> 35.<telerikGrid:GridViewDataColumn Header="Resume Required" 36.DataMemberBinding="{Binding NeedsResume}" 37.UniqueName="NeedsResume" /> 38.<telerikGrid:GridViewDataColumn Header="CV Required" 39.DataMemberBinding="{Binding NeedsCV}" 40.UniqueName="NeedsCV" /> 41.<telerikGrid:GridViewDataColumn Header="Overview Required" 42.DataMemberBinding="{Binding NeedsOverview}" 43.UniqueName="NeedsOverview" /> 44.<telerikGrid:GridViewDataColumn Header="Active" 45.DataMemberBinding="{Binding IsActive}" 46.UniqueName="IsActive" /> 47.</telerikGrid:RadGridView.Columns> 48.</telerikGrid:RadGridView> 49.</Grid> I'll explain what's happening here by line numbers: Lines 11 and 16: Using the same type of click commands as we saw in the Menu module, we tie the button clicks to delegate commands in the viewmodel. Line 25: The source for the jobs will be a collection in the viewmodel. Line 26: We also bind the selected item to a public property from the viewmodel for use in code. Line 27: We've turned the event into a command so we can handle it via code in the viewmodel. So those first three probably make sense to you as far as Silverlight/WPF binding magic is concerned, but for line 27... This actually comes from something I read onDamien Schenkelman's blog back in the day for creating an attached behavior from any event. So, any time you see me using command:Whatever.Command, the backing for it is actually something like this: SelectedItemChangedEventBehavior.cs: 01.public class SelectedItemChangedEventBehavior : CommandBehaviorBase<Telerik.Windows.Controls.DataControl> 02.{ 03.public SelectedItemChangedEventBehavior(DataControl element) 04.: base(element) 05.{ 06.element.SelectionChanged += new EventHandler<SelectionChangeEventArgs>(element_SelectionChanged); 07.} 08.void element_SelectionChanged(object sender, SelectionChangeEventArgs e) 09.{ 10.// We'll only ever allow single selection, so will only need item index 0 11.base.CommandParameter = e.AddedItems[0]; 12.base.ExecuteCommand(); 13.} 14.} SelectedItemChangedEventClass.cs: 01.public class SelectedItemChangedEventClass 02.{ 03.#region The Command Stuff 04.public static ICommand GetCommand(DependencyObject obj) 05.{ 06.return (ICommand)obj.GetValue(CommandProperty); 07.} 08.public static void SetCommand(DependencyObject obj, ICommand value) 09.{ 10.obj.SetValue(CommandProperty, value); 11.} 12.public static readonly DependencyProperty CommandProperty = 13.DependencyProperty.RegisterAttached("Command", typeof(ICommand), 14.typeof(SelectedItemChangedEventClass), new PropertyMetadata(OnSetCommandCallback)); 15.public static void OnSetCommandCallback(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs e) 16.{ 17.DataControl element = dependencyObject as DataControl; 18.if (element != null) 19.{ 20.SelectedItemChangedEventBehavior behavior = GetOrCreateBehavior(element); 21.behavior.Command = e.NewValue as ICommand; 22.} 23.} 24.#endregion 25.public static SelectedItemChangedEventBehavior GetOrCreateBehavior(DataControl element) 26.{ 27.SelectedItemChangedEventBehavior behavior = element.GetValue(SelectedItemChangedEventBehaviorProperty) as SelectedItemChangedEventBehavior; 28.if (behavior == null) 29.{ 30.behavior = new SelectedItemChangedEventBehavior(element); 31.element.SetValue(SelectedItemChangedEventBehaviorProperty, behavior); 32.} 33.return behavior; 34.} 35.public static SelectedItemChangedEventBehavior GetSelectedItemChangedEventBehavior(DependencyObject obj) 36.{ 37.return (SelectedItemChangedEventBehavior)obj.GetValue(SelectedItemChangedEventBehaviorProperty); 38.} 39.public static void SetSelectedItemChangedEventBehavior(DependencyObject obj, SelectedItemChangedEventBehavior value) 40.{ 41.obj.SetValue(SelectedItemChangedEventBehaviorProperty, value); 42.} 43.public static readonly DependencyProperty SelectedItemChangedEventBehaviorProperty = 44.DependencyProperty.RegisterAttached("SelectedItemChangedEventBehavior", 45.typeof(SelectedItemChangedEventBehavior), typeof(SelectedItemChangedEventClass), null); 46.} These end up looking very similar from command to command, but in a nutshell you create a command based on any event, determine what the parameter for it will be, then execute. It attaches via XAML and ties to a DelegateCommand in the viewmodel, so you get the full event experience (since some controls get a bit event-rich for added functionality). Simple enough, right? Viewmodel for the Job Posting View The Viewmodel is going to need to handle all events going back and forth, maintaining interactions with the data we are using, and both publishing and subscribing to events. Rather than breaking this into tons of little pieces, I'll give you a nice view of the entire viewmodel and then hit up the important points line-by-line: 001.public class JobPostingViewModel : ViewModelBase 002.{ 003.private readonly IEventAggregator eventAggregator; 004.private readonly IRegionManager regionManager; 005.public DelegateCommand<object> AddRecord { get; set; } 006.public DelegateCommand<object> EditRecord { get; set; } 007.public DelegateCommand<object> SelectedItemChanged { get; set; } 008.public RecruitingContext context; 009.private QueryableCollectionView _myJobs; 010.public QueryableCollectionView MyJobs 011.{ 012.get { return _myJobs; } 013.} 014.private QueryableCollectionView _selectionJobActionHistory; 015.public QueryableCollectionView SelectedJobActionHistory 016.{ 017.get { return _selectionJobActionHistory; } 018.} 019.private JobPosting _selectedJob; 020.public JobPosting SelectedJob 021.{ 022.get { return _selectedJob; } 023.set 024.{ 025.if (value != _selectedJob) 026.{ 027._selectedJob = value; 028.NotifyChanged("SelectedJob"); 029.} 030.} 031.} 032.public SubscriptionToken editToken = new SubscriptionToken(); 033.public SubscriptionToken addToken = new SubscriptionToken(); 034.public JobPostingViewModel(IEventAggregator eventAgg, IRegionManager regionmanager) 035.{ 036.// set Unity items 037.this.eventAggregator = eventAgg; 038.this.regionManager = regionmanager; 039.// load our context 040.context = new RecruitingContext(); 041.this._myJobs = new QueryableCollectionView(context.JobPostings); 042.context.Load(context.GetJobPostingsQuery()); 043.// set command events 044.this.AddRecord = new DelegateCommand<object>(this.AddNewRecord); 045.this.EditRecord = new DelegateCommand<object>(this.EditExistingRecord); 046.this.SelectedItemChanged = new DelegateCommand<object>(this.SelectedRecordChanged); 047.SetSubscriptions(); 048.} 049.#region DelegateCommands from View 050.public void AddNewRecord(object obj) 051.{ 052.this.eventAggregator.GetEvent<AddJobEvent>().Publish(true); 053.} 054.public void EditExistingRecord(object obj) 055.{ 056.if (_selectedJob == null) 057.{ 058.this.eventAggregator.GetEvent<NotifyUserEvent>().Publish("No job selected."); 059.} 060.else 061.{ 062.this._myJobs.EditItem(this._selectedJob); 063.this.eventAggregator.GetEvent<EditJobEvent>().Publish(this._selectedJob); 064.} 065.} 066.public void SelectedRecordChanged(object obj) 067.{ 068.if (obj.GetType() == typeof(ActionHistory)) 069.{ 070.// event bubbles up so we don't catch items from the ActionHistory grid 071.} 072.else 073.{ 074.JobPosting job = obj as JobPosting; 075.GrabHistory(job.PostingID); 076.} 077.} 078.#endregion 079.#region Subscription Declaration and Events 080.public void SetSubscriptions() 081.{ 082.EditJobCompleteEvent editComplete = eventAggregator.GetEvent<EditJobCompleteEvent>(); 083.if (editToken != null) 084.editComplete.Unsubscribe(editToken); 085.editToken = editComplete.Subscribe(this.EditCompleteEventHandler); 086.AddJobCompleteEvent addComplete = eventAggregator.GetEvent<AddJobCompleteEvent>(); 087.if (addToken != null) 088.addComplete.Unsubscribe(addToken); 089.addToken = addComplete.Subscribe(this.AddCompleteEventHandler); 090.} 091.public void EditCompleteEventHandler(bool complete) 092.{ 093.if (complete) 094.{ 095.JobPosting thisJob = _myJobs.CurrentEditItem as JobPosting; 096.this._myJobs.CommitEdit(); 097.this.context.SubmitChanges((s) => 098.{ 099.ActionHistory myAction = new ActionHistory(); 100.myAction.PostingID = thisJob.PostingID; 101.myAction.Description = String.Format("Job '{0}' has been edited by {1}", thisJob.JobTitle, "default user"); 102.myAction.TimeStamp = DateTime.Now; 103.eventAggregator.GetEvent<AddActionEvent>().Publish(myAction); 104.} 105., null); 106.} 107.else 108.{ 109.this._myJobs.CancelEdit(); 110.} 111.this.MakeMeActive(this.regionManager, "MainRegion", "JobPostingsView"); 112.} 113.public void AddCompleteEventHandler(JobPosting job) 114.{ 115.if (job == null) 116.{ 117.// do nothing, new job add cancelled 118.} 119.else 120.{ 121.this.context.JobPostings.Add(job); 122.this.context.SubmitChanges((s) => 123.{ 124.ActionHistory myAction = new ActionHistory(); 125.myAction.PostingID = job.PostingID; 126.myAction.Description = String.Format("Job '{0}' has been added by {1}", job.JobTitle, "default user"); 127.myAction.TimeStamp = DateTime.Now; 128.eventAggregator.GetEvent<AddActionEvent>().Publish(myAction); 129.} 130., null); 131.} 132.this.MakeMeActive(this.regionManager, "MainRegion", "JobPostingsView"); 133.} 134.#endregion 135.public void GrabHistory(int postID) 136.{ 137.context.ActionHistories.Clear(); 138._selectionJobActionHistory = new QueryableCollectionView(context.ActionHistories); 139.context.Load(context.GetHistoryForJobQuery(postID)); 140.} Taking it from the top, we're injecting an Event Aggregator and Region Manager for use down the road and also have the public DelegateCommands (just like in the Menu module). We also grab a reference to our context, which we'll obviously need for data, then set up a few fields with public properties tied to them. We're also setting subscription tokens, which we have not yet seen but I will get into below. The AddNewRecord (50) and EditExistingRecord (54) methods should speak for themselves for functionality, the one thing of note is we're sending events off to the Event Aggregator which some module, somewhere will take care of. Since these aren't entirely relying on one another, the Jobs View doesn't care if anyone is listening, but it will publish AddJobEvent (52), NotifyUserEvent (58) and EditJobEvent (63)regardless. Don't mind the GrabHistory() method so much, that is just grabbing history items (visibly being created in the SubmitChanges callbacks), and adding them to the database. Every action will trigger a history event, so we'll know who modified what and when, just in case. ;) So where are we at? Well, if we click to Add a job, we publish an event, if we edit a job, we publish an event with the selected record (attained through the magic of binding). Where is this all going though? To the Viewmodel, of course! XAML for the AddEditJobView This is pretty straightforward except for one thing, noted below: 001.<Grid x:Name="LayoutRoot" 002.Background="White"> 003.<Grid x:Name="xEditGrid" 004.Margin="10" 005.validationHelper:ValidationScope.Errors="{Binding Errors}"> 006.<Grid.Background> 007.<LinearGradientBrush EndPoint="0.5,1" 008.StartPoint="0.5,0"> 009.<GradientStop Color="#FFC7C7C7" 010.Offset="0" /> 011.<GradientStop Color="#FFF6F3F3" 012.Offset="1" /> 013.</LinearGradientBrush> 014.</Grid.Background> 015.<Grid.RowDefinitions> 016.<RowDefinition Height="40" /> 017.<RowDefinition Height="40" /> 018.<RowDefinition Height="40" /> 019.<RowDefinition Height="100" /> 020.<RowDefinition Height="100" /> 021.<RowDefinition Height="100" /> 022.<RowDefinition Height="40" /> 023.<RowDefinition Height="40" /> 024.<RowDefinition Height="40" /> 025.</Grid.RowDefinitions> 026.<Grid.ColumnDefinitions> 027.<ColumnDefinition Width="150" /> 028.<ColumnDefinition Width="150" /> 029.<ColumnDefinition Width="300" /> 030.<ColumnDefinition Width="100" /> 031.</Grid.ColumnDefinitions> 032.<!-- Title --> 033.<TextBlock Margin="8" 034.Text="{Binding AddEditString}" 035.TextWrapping="Wrap" 036.Grid.Column="1" 037.Grid.ColumnSpan="2" 038.FontSize="16" /> 039.<!-- Data entry area--> 040. 041.<TextBlock Margin="8,0,0,0" 042.Style="{StaticResource LabelTxb}" 043.Grid.Row="1" 044.Text="Job Title" 045.VerticalAlignment="Center" /> 046.<TextBox x:Name="xJobTitleTB" 047.Margin="0,8" 048.Grid.Column="1" 049.Grid.Row="1" 050.Text="{Binding activeJob.JobTitle, Mode=TwoWay, NotifyOnValidationError=True, ValidatesOnExceptions=True}" 051.Grid.ColumnSpan="2" /> 052.<TextBlock Margin="8,0,0,0" 053.Grid.Row="2" 054.Text="Location" 055.d:LayoutOverrides="Height" 056.VerticalAlignment="Center" /> 057.<TextBox x:Name="xLocationTB" 058.Margin="0,8" 059.Grid.Column="1" 060.Grid.Row="2" 061.Text="{Binding activeJob.Location, Mode=TwoWay, NotifyOnValidationError=True, ValidatesOnExceptions=True}" 062.Grid.ColumnSpan="2" /> 063. 064.<TextBlock Margin="8,11,8,0" 065.Grid.Row="3" 066.Text="Description" 067.TextWrapping="Wrap" 068.VerticalAlignment="Top" /> 069. 070.<TextBox x:Name="xDescriptionTB" 071.Height="84" 072.TextWrapping="Wrap" 073.ScrollViewer.VerticalScrollBarVisibility="Auto" 074.Grid.Column="1" 075.Grid.Row="3" 076.Text="{Binding activeJob.Description, Mode=TwoWay, NotifyOnValidationError=True, ValidatesOnExceptions=True}" 077.Grid.ColumnSpan="2" /> 078.<TextBlock Margin="8,11,8,0" 079.Grid.Row="4" 080.Text="Requirements" 081.TextWrapping="Wrap" 082.VerticalAlignment="Top" /> 083. 084.<TextBox x:Name="xRequirementsTB" 085.Height="84" 086.TextWrapping="Wrap" 087.ScrollViewer.VerticalScrollBarVisibility="Auto" 088.Grid.Column="1" 089.Grid.Row="4" 090.Text="{Binding activeJob.Requirements, Mode=TwoWay, NotifyOnValidationError=True, ValidatesOnExceptions=True}" 091.Grid.ColumnSpan="2" /> 092.<TextBlock Margin="8,11,8,0" 093.Grid.Row="5" 094.Text="Qualifications" 095.TextWrapping="Wrap" 096.VerticalAlignment="Top" /> 097. 098.<TextBox x:Name="xQualificationsTB" 099.Height="84" 100.TextWrapping="Wrap" 101.ScrollViewer.VerticalScrollBarVisibility="Auto" 102.Grid.Column="1" 103.Grid.Row="5" 104.Text="{Binding activeJob.Qualifications, Mode=TwoWay, NotifyOnValidationError=True, ValidatesOnExceptions=True}" 105.Grid.ColumnSpan="2" /> 106.<!-- Requirements Checkboxes--> 107. 108.<CheckBox x:Name="xResumeRequiredCB" Margin="8,8,8,15" 109.Content="Resume Required" 110.Grid.Row="6" 111.Grid.ColumnSpan="2" 112.IsChecked="{Binding activeJob.NeedsResume, Mode=TwoWay, NotifyOnValidationError=True, ValidatesOnExceptions=True}"/> 113. 114.<CheckBox x:Name="xCoverletterRequiredCB" Margin="8,8,8,15" 115.Content="Cover Letter Required" 116.Grid.Column="2" 117.Grid.Row="6" 118.IsChecked="{Binding activeJob.NeedsCV, Mode=TwoWay, NotifyOnValidationError=True, ValidatesOnExceptions=True}"/> 119. 120.<CheckBox x:Name="xOverviewRequiredCB" Margin="8,8,8,15" 121.Content="Overview Required" 122.Grid.Row="7" 123.Grid.ColumnSpan="2" 124.IsChecked="{Binding activeJob.NeedsOverview, Mode=TwoWay, NotifyOnValidationError=True, ValidatesOnExceptions=True}"/> 125. 126.<CheckBox x:Name="xJobActiveCB" Margin="8,8,8,15" 127.Content="Job is Active" 128.Grid.Column="2" 129.Grid.Row="7" 130.IsChecked="{Binding activeJob.IsActive, Mode=TwoWay, NotifyOnValidationError=True, ValidatesOnExceptions=True}"/> 131. 132.<!-- Buttons --> 133. 134.<Button x:Name="xAddEditButton" Margin="8,8,0,10" 135.Content="{Binding AddEditButtonString}" 136.cal:Click.Command="{Binding AddEditCommand}" 137.Grid.Column="2" 138.Grid.Row="8" 139.HorizontalAlignment="Left" 140.Width="125" 141.telerik:StyleManager.Theme="Windows7" /> 142. 143.<Button x:Name="xCancelButton" HorizontalAlignment="Right" 144.Content="Cancel" 145.cal:Click.Command="{Binding CancelCommand}" 146.Margin="0,8,8,10" 147.Width="125" 148.Grid.Column="2" 149.Grid.Row="8" 150.telerik:StyleManager.Theme="Windows7" /> 151.</Grid> 152.</Grid> The 'validationHelper:ValidationScope' line may seem odd. This is a handy little trick for catching current and would-be validation errors when working in this whole setup. This all comes from an approach found on theJoy Of Code blog, although it looks like the story for this will be changing slightly with new advances in SL4/WCF RIA Services, so this section can definitely get an overhaul a little down the road. The code is the fun part of all this, so let us see what's happening under the hood. Viewmodel for the AddEditJobView We are going to see some of the same things happening here, so I'll skip over the repeat info and get right to the good stuff: 001.public class AddEditJobViewModel : ViewModelBase 002.{ 003.private readonly IEventAggregator eventAggregator; 004.private readonly IRegionManager regionManager; 005. 006.public RecruitingContext context; 007. 008.private JobPosting _activeJob; 009.public JobPosting activeJob 010.{ 011.get { return _activeJob; } 012.set 013.{ 014.if (_activeJob != value) 015.{ 016._activeJob = value; 017.NotifyChanged("activeJob"); 018.} 019.} 020.} 021. 022.public bool isNewJob; 023. 024.private string _addEditString; 025.public string AddEditString 026.{ 027.get { return _addEditString; } 028.set 029.{ 030.if (_addEditString != value) 031.{ 032._addEditString = value; 033.NotifyChanged("AddEditString"); 034.} 035.} 036.} 037. 038.private string _addEditButtonString; 039.public string AddEditButtonString 040.{ 041.get { return _addEditButtonString; } 042.set 043.{ 044.if (_addEditButtonString != value) 045.{ 046._addEditButtonString = value; 047.NotifyChanged("AddEditButtonString"); 048.} 049.} 050.} 051. 052.public SubscriptionToken addJobToken = new SubscriptionToken(); 053.public SubscriptionToken editJobToken = new SubscriptionToken(); 054. 055.public DelegateCommand<object> AddEditCommand { get; set; } 056.public DelegateCommand<object> CancelCommand { get; set; } 057. 058.private ObservableCollection<ValidationError> _errors = new ObservableCollection<ValidationError>(); 059.public ObservableCollection<ValidationError> Errors 060.{ 061.get { return _errors; } 062.} 063. 064.private ObservableCollection<ValidationResult> _valResults = new ObservableCollection<ValidationResult>(); 065.public ObservableCollection<ValidationResult> ValResults 066.{ 067.get { return this._valResults; } 068.} 069. 070.public AddEditJobViewModel(IEventAggregator eventAgg, IRegionManager regionmanager) 071.{ 072.// set Unity items 073.this.eventAggregator = eventAgg; 074.this.regionManager = regionmanager; 075. 076.context = new RecruitingContext(); 077. 078.AddEditCommand = new DelegateCommand<object>(this.AddEditJobCommand); 079.CancelCommand = new DelegateCommand<object>(this.CancelAddEditCommand); 080. 081.SetSubscriptions(); 082.} 083. 084.#region Subscription Declaration and Events 085. 086.public void SetSubscriptions() 087.{ 088.AddJobEvent addJob = this.eventAggregator.GetEvent<AddJobEvent>(); 089. 090.if (addJobToken != null) 091.addJob.Unsubscribe(addJobToken); 092. 093.addJobToken = addJob.Subscribe(this.AddJobEventHandler); 094. 095.EditJobEvent editJob = this.eventAggregator.GetEvent<EditJobEvent>(); 096. 097.if (editJobToken != null) 098.editJob.Unsubscribe(editJobToken); 099. 100.editJobToken = editJob.Subscribe(this.EditJobEventHandler); 101.} 102. 103.public void AddJobEventHandler(bool isNew) 104.{ 105.this.activeJob = null; 106.this.activeJob = new JobPosting(); 107.this.activeJob.IsActive = true; // We assume that we want a new job to go up immediately 108.this.isNewJob = true; 109.this.AddEditString = "Add New Job Posting"; 110.this.AddEditButtonString = "Add Job"; 111. 112.MakeMeActive(this.regionManager, "MainRegion", "AddEditJobView"); 113.} 114. 115.public void EditJobEventHandler(JobPosting editJob) 116.{ 117.this.activeJob = null; 118.this.activeJob = editJob; 119.this.isNewJob = false; 120.this.AddEditString = "Edit Job Posting"; 121.this.AddEditButtonString = "Edit Job"; 122. 123.MakeMeActive(this.regionManager, "MainRegion", "AddEditJobView"); 124.} 125. 126.#endregion 127. 128.#region DelegateCommands from View 129. 130.public void AddEditJobCommand(object obj) 131.{ 132.if (this.Errors.Count > 0) 133.{ 134.List<string> errorMessages = new List<string>(); 135. 136.foreach (var valR in this.Errors) 137.{ 138.errorMessages.Add(valR.Exception.Message); 139.} 140. 141.this.eventAggregator.GetEvent<DisplayValidationErrorsEvent>().Publish(errorMessages); 142. 143.} 144.else if (!Validator.TryValidateObject(this.activeJob, new ValidationContext(this.activeJob, null, null), _valResults, true)) 145.{ 146.List<string> errorMessages = new List<string>(); 147. 148.foreach (var valR in this._valResults) 149.{ 150.errorMessages.Add(valR.ErrorMessage); 151.} 152. 153.this._valResults.Clear(); 154. 155.this.eventAggregator.GetEvent<DisplayValidationErrorsEvent>().Publish(errorMessages); 156.} 157.else 158.{ 159.if (this.isNewJob) 160.{ 161.this.eventAggregator.GetEvent<AddJobCompleteEvent>().Publish(this.activeJob); 162.} 163.else 164.{ 165.this.eventAggregator.GetEvent<EditJobCompleteEvent>().Publish(true); 166.} 167.} 168.} 169. 170.public void CancelAddEditCommand(object obj) 171.{ 172.if (this.isNewJob) 173.{ 174.this.eventAggregator.GetEvent<AddJobCompleteEvent>().Publish(null); 175.} 176.else 177.{ 178.this.eventAggregator.GetEvent<EditJobCompleteEvent>().Publish(false); 179.} 180.} 181. 182.#endregion 183.} 184.} We start seeing something new on line 103- the AddJobEventHandler will create a new job and set that to the activeJob item on the ViewModel. When this is all set, the view calls that familiar MakeMeActive method to activate itself. I made a bit of a management call on making views self-activate like this, but I figured it works for one reason. As I create this application, views may not exist that I have in mind, so after a view receives its 'ping' from being subscribed to an event, it prepares whatever it needs to do and then goes active. This way if I don't have 'edit' hooked up, I can click as the day is long on the main view and won't get lost in an empty region. Total personal preference here. :) Everything else should again be pretty straightforward, although I do a bit of validation checking in the AddEditJobCommand, which can either fire off an event back to the main view/viewmodel if everything is a success or sent a list of errors to our notification module, which pops open a RadWindow with the alerts if any exist. As a bonus side note, here's what my WCF RIA Services metadata looks like for handling all of the validation: private JobPostingMetadata() { } [StringLength(2500, ErrorMessage = "Description should be more than one and less than 2500 characters.", MinimumLength = 1)] [Required(ErrorMessage = "Description is required.")] public string Description; [Required(ErrorMessage="Active Status is Required")] public bool IsActive; [StringLength(100, ErrorMessage = "Posting title must be more than 3 but less than 100 characters.", MinimumLength = 3)] [Required(ErrorMessage = "Job Title is required.")] public bool JobTitle; [Required] public string Location; public bool NeedsCV; public bool NeedsOverview; public bool NeedsResume; public int PostingID; [Required(ErrorMessage="Qualifications are required.")] [StringLength(2500, ErrorMessage="Qualifications should be more than one and less than 2500 characters.", MinimumLength=1)] public string Qualifications; [StringLength(2500, ErrorMessage = "Requirements should be more than one and less than 2500 characters.", MinimumLength = 1)] [Required(ErrorMessage="Requirements are required.")] public string Requirements;   The RecruitCB Alternative See all that Xaml I pasted above? Those are now two pieces sitting in the JobsView.xaml file now. The only real difference is that the xEditGrid now sits in the same place as xJobsGrid, with visibility swapping out between the two for a quick switch. I also took out all the cal: and command: command references and replaced Button events with clicks and the Grid selection command replaced with a SelectedItemChanged event. Also, at the bottom of the xEditGrid after the last button, I add a ValidationSummary (with Visibility=Collapsed) to catch any errors that are popping up. Simple as can be, and leads to this being the single code-behind file: 001.public partial class JobsView : UserControl 002.{ 003.public RecruitingContext context; 004.public JobPosting activeJob; 005.public bool isNew; 006.private ObservableCollection<ValidationResult> _valResults = new ObservableCollection<ValidationResult>(); 007.public ObservableCollection<ValidationResult> ValResults 008.{ 009.get { return this._valResults; } 010.} 011.public JobsView() 012.{ 013.InitializeComponent(); 014.this.Loaded += new RoutedEventHandler(JobsView_Loaded); 015.} 016.void JobsView_Loaded(object sender, RoutedEventArgs e) 017.{ 018.context = new RecruitingContext(); 019.xJobsGrid.ItemsSource = context.JobPostings; 020.context.Load(context.GetJobPostingsQuery()); 021.} 022.private void xAddRecordButton_Click(object sender, RoutedEventArgs e) 023.{ 024.activeJob = new JobPosting(); 025.isNew = true; 026.xAddEditTitle.Text = "Add a Job Posting"; 027.xAddEditButton.Content = "Add"; 028.xEditGrid.DataContext = activeJob; 029.HideJobsGrid(); 030.} 031.private void xEditRecordButton_Click(object sender, RoutedEventArgs e) 032.{ 033.activeJob = xJobsGrid.SelectedItem as JobPosting; 034.isNew = false; 035.xAddEditTitle.Text = "Edit a Job Posting"; 036.xAddEditButton.Content = "Edit"; 037.xEditGrid.DataContext = activeJob; 038.HideJobsGrid(); 039.} 040.private void xAddEditButton_Click(object sender, RoutedEventArgs e) 041.{ 042.if (!Validator.TryValidateObject(this.activeJob, new ValidationContext(this.activeJob, null, null), _valResults, true)) 043.{ 044.List<string> errorMessages = new List<string>(); 045.foreach (var valR in this._valResults) 046.{ 047.errorMessages.Add(valR.ErrorMessage); 048.} 049.this._valResults.Clear(); 050.ShowErrors(errorMessages); 051.} 052.else if (xSummary.Errors.Count > 0) 053.{ 054.List<string> errorMessages = new List<string>(); 055.foreach (var err in xSummary.Errors) 056.{ 057.errorMessages.Add(err.Message); 058.} 059.ShowErrors(errorMessages); 060.} 061.else 062.{ 063.if (this.isNew) 064.{ 065.context.JobPostings.Add(activeJob); 066.context.SubmitChanges((s) => 067.{ 068.ActionHistory thisAction = new ActionHistory(); 069.thisAction.PostingID = activeJob.PostingID; 070.thisAction.Description = String.Format("Job '{0}' has been edited by {1}", activeJob.JobTitle, "default user"); 071.thisAction.TimeStamp = DateTime.Now; 072.context.ActionHistories.Add(thisAction); 073.context.SubmitChanges(); 074.}, null); 075.} 076.else 077.{ 078.context.SubmitChanges((s) => 079.{ 080.ActionHistory thisAction = new ActionHistory(); 081.thisAction.PostingID = activeJob.PostingID; 082.thisAction.Description = String.Format("Job '{0}' has been added by {1}", activeJob.JobTitle, "default user"); 083.thisAction.TimeStamp = DateTime.Now; 084.context.ActionHistories.Add(thisAction); 085.context.SubmitChanges(); 086.}, null); 087.} 088.ShowJobsGrid(); 089.} 090.} 091.private void xCancelButton_Click(object sender, RoutedEventArgs e) 092.{ 093.ShowJobsGrid(); 094.} 095.private void ShowJobsGrid() 096.{ 097.xAddEditRecordButtonPanel.Visibility = Visibility.Visible; 098.xEditGrid.Visibility = Visibility.Collapsed; 099.xJobsGrid.Visibility = Visibility.Visible; 100.} 101.private void HideJobsGrid() 102.{ 103.xAddEditRecordButtonPanel.Visibility = Visibility.Collapsed; 104.xJobsGrid.Visibility = Visibility.Collapsed; 105.xEditGrid.Visibility = Visibility.Visible; 106.} 107.private void ShowErrors(List<string> errorList) 108.{ 109.string nm = "Errors received: \n"; 110.foreach (string anerror in errorList) 111.nm += anerror + "\n"; 112.RadWindow.Alert(nm); 113.} 114.} The first 39 lines should be pretty familiar, not doing anything too unorthodox to get this up and running. Once we hit the xAddEditButton_Click on line 40, we're still doing pretty much the same things except instead of checking the ValidationHelper errors, we both run a check on the current activeJob object as well as check the ValidationSummary errors list. Once that is set, we again use the callback of context.SubmitChanges (lines 68 and 78) to create an ActionHistory which we will use to track these items down the line. That's all? Essentially... yes. If you look back through this post, most of the code and adventures we have taken were just to get things working in the MVVM/Prism setup. Since I have the whole 'module' self-contained in a single JobView+code-behind setup, I don't have to worry about things like sending events off into space for someone to pick up, communicating through an Infrastructure project, or even re-inventing events to be used with attached behaviors. Everything just kinda works, and again with much less code. Here's a picture of the MVVM and Code-behind versions on the Jobs and AddEdit views, but since the functionality is the same in both apps you still cannot tell them apart (for two-strike): Looking ahead, the Applicants module is effectively the same thing as the Jobs module, so most of the code is being cut-and-pasted back and forth with minor tweaks here and there. So that one is being taken care of by me behind the scenes. Next time, we get into a new world of fun- the interview scheduling module, which will pull from available jobs and applicants for each interview being scheduled, tying everything together with RadScheduler to the rescue. Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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• Command Pattern : How to pass parameters to a command ?

  - by Romain Verdier

  My question is related to the command pattern, where we have the following abstraction (C# code) : public interface ICommand { Execute(); } Let's take a simple concrete command, which aims to delete an entity from our application. A Person instance, for example. I'll have a DeletePersonCommand, which implements ICommand. This command needs the Person to delete as a parameter, in order to delete it when Execute method is called. What is the best way to manage parametrized commands ? How to pass parameters to commands, before executing them ?

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• Building applications with WPF, MVVM and Prism(aka CAG)

  - by skjagini

  In this article I am going to walk through an application using WPF and Prism (aka composite application guidance, CAG) which simulates engaging a taxi (cab).  The rules are simple, the app would have3 screens A login screen to authenticate the user An information screen. A screen to engage the cab and roam around and calculating the total fare Metered Rate of Fare The meter is required to be engaged when a cab is occupied by anyone $3.00 upon entry $0.35 for each additional unit The unit fare is: one-fifth of a mile, when the cab is traveling at 6 miles an hour or more; or 60 seconds when not in motion or traveling at less than 12 miles per hour. Night surcharge of $.50 after 8:00 PM & before 6:00 AM Peak hour Weekday Surcharge of $1.00 Monday - Friday after 4:00 PM & before 8:00 PM New York State Tax Surcharge of $.50 per ride. Example: Friday (2010-10-08) 5:30pm Start at Lexington Ave & E 57th St End at Irving Pl & E 15th St Start = $3.00 Travels 2 miles at less than 6 mph for 15 minutes = $3.50 Travels at more than 12 mph for 5 minutes = $1.75 Peak hour Weekday Surcharge = $1.00 (ride started at 5:30 pm) New York State Tax Surcharge = $0.50 Before we dive into the app, I would like to give brief description about the framework.  If you want to jump on to the source code, scroll all the way to the end of the post. MVVM MVVM pattern is in no way related to the usage of PRISM in your application and should be considered if you are using WPF irrespective of PRISM or not. Lets say you are not familiar with MVVM, your typical UI would involve adding some UI controls like text boxes, a button, double clicking on the button,  generating event handler, calling a method from business layer and updating the user interface, it works most of the time for developing small scale applications. The problem with this approach is that there is some amount of code specific to business logic wrapped in UI specific code which is hard to unit test it, mock it and MVVM helps to solve the exact problem. MVVM stands for Model(M) – View(V) – ViewModel(VM),  based on the interactions with in the three parties it should be called VVMM,  MVVM sounds more like MVC (Model-View-Controller) so the name. Why it should be called VVMM: View – View Model - Model WPF allows to create user interfaces using XAML and MVVM takes it to the next level by allowing complete separation of user interface and business logic. In WPF each view will have a property, DataContext when set to an instance of a class (which happens to be your view model) provides the data the view is interested in, i.e., view interacts with view model and at the same time view model interacts with view through DataContext. Sujith, if view and view model are interacting directly with each other how does MVVM is helping me separation of concerns? Well, the catch is DataContext is of type Object, since it is of type object view doesn’t know exact type of view model allowing views and views models to be loosely coupled. View models aggregate data from models (data access layer, services, etc) and make it available for views through properties, methods etc, i.e., View Models interact with Models. PRISM Prism is provided by Microsoft Patterns and Practices team and it can be downloaded from codeplex for source code,  samples and documentation on msdn.  The name composite implies, to compose user interface from different modules (views) without direct dependencies on each other, again allowing  loosely coupled development. Well Sujith, I can already do that with user controls, why shall I learn another framework?  That’s correct, you can decouple using user controls, but you still have to manage some amount of coupling, like how to do you communicate between the controls, how do you subscribe/unsubscribe, loading/unloading views dynamically. Prism is not a replacement for user controls, provides the following features which greatly help in designing the composite applications. Dependency Injection (DI)/ Inversion of Control (IoC) Modules Regions Event Aggregator  Commands Simply put, MVVM helps building a single view and Prism helps building an application using the views There are other open source alternatives to Prism, like MVVMLight, Cinch, take a look at them as well. Lets dig into the source code.  1. Solution The solution is made of the following projects Framework: Holds the common functionality in building applications using WPF and Prism TaxiClient: Start up project, boot strapping and app styling TaxiCommon: Helps with the business logic TaxiModules: Holds the meat of the application with views and view models TaxiTests: To test the application 2. DI / IoC Dependency Injection (DI) as the name implies refers to injecting dependencies and Inversion of Control (IoC) means the calling code has no direct control on the dependencies, opposite of normal way of programming where dependencies are passed by caller, i.e inversion; aside from some differences in terminology the concept is same in both the cases. The idea behind DI/IoC pattern is to reduce the amount of direct coupling between different components of the application, the higher the dependency the more tightly coupled the application resulting in code which is hard to modify, unit test and mock.  Initializing Dependency Injection through BootStrapper TaxiClient is the starting project of the solution and App (App.xaml)  is the starting class that gets called when you run the application. From the App’s OnStartup method we will invoke BootStrapper.   namespace TaxiClient { /// <summary> /// Interaction logic for App.xaml /// </summary> public partial class App : Application { protected override void OnStartup(StartupEventArgs e) { base.OnStartup(e);   (new BootStrapper()).Run(); } } } BootStrapper is your contact point for initializing the application including dependency injection, creating Shell and other frameworks. We are going to use Unity for DI and there are lot of open source DI frameworks like Spring.Net, StructureMap etc with different feature set  and you can choose a framework based on your preferences. Note that Prism comes with in built support for Unity, for example we are deriving from UnityBootStrapper in our case and for any other DI framework you have to extend the Prism appropriately   namespace TaxiClient { public class BootStrapper: UnityBootstrapper { protected override IModuleCatalog CreateModuleCatalog() { return new ConfigurationModuleCatalog(); } protected override DependencyObject CreateShell() { Framework.FrameworkBootStrapper.Run(Container, Application.Current.Dispatcher);   Shell shell = new Shell(); shell.ResizeMode = ResizeMode.NoResize; shell.Show();   return shell; } } } Lets take a look into  FrameworkBootStrapper to check out how to register with unity container. namespace Framework { public class FrameworkBootStrapper { public static void Run(IUnityContainer container, Dispatcher dispatcher) { UIDispatcher uiDispatcher = new UIDispatcher(dispatcher); container.RegisterInstance<IDispatcherService>(uiDispatcher);   container.RegisterType<IInjectSingleViewService, InjectSingleViewService>( new ContainerControlledLifetimeManager());   . . . } } } In the above code we are registering two components with unity container. You shall observe that we are following two different approaches, RegisterInstance and RegisterType.  With RegisterInstance we are registering an existing instance and the same instance will be returned for every request made for IDispatcherService   and with RegisterType we are requesting unity container to create an instance for us when required, i.e., when I request for an instance for IInjectSingleViewService, unity will create/return an instance of InjectSingleViewService class and with RegisterType we can configure the life time of the instance being created. With ContaienrControllerLifetimeManager, the unity container caches the instance and reuses for any subsequent requests, without recreating a new instance. Lets take a look into FareViewModel.cs and it’s constructor. The constructor takes one parameter IEventAggregator and if you try to find all references in your solution for IEventAggregator, you will not find a single location where an instance of EventAggregator is passed directly to the constructor. The compiler still finds an instance and works fine because Prism is already configured when used with Unity container to return an instance of EventAggregator when requested for IEventAggregator and in this particular case it is called constructor injection. public class FareViewModel:ObservableBase, IDataErrorInfo { ... private IEventAggregator _eventAggregator;   public FareViewModel(IEventAggregator eventAggregator) { _eventAggregator = eventAggregator; InitializePropertyNames(); InitializeModel(); PropertyChanged += OnPropertyChanged; } ... 3. Shell Shells are very similar in operation to Master Pages in asp.net or MDI in Windows Forms. And shells contain regions which display the views, you can have as many regions as you wish in a given view. You can also nest regions. i.e, one region can load a view which in itself may contain other regions. We have to create a shell at the start of the application and are doing it by overriding CreateShell method from BootStrapper From the following Shell.xaml you shall notice that we have two content controls with Region names as ‘MenuRegion’ and ‘MainRegion’.  The idea here is that you can inject any user controls into the regions dynamically, i.e., a Menu User Control for MenuRegion and based on the user action you can load appropriate view into MainRegion.    <Window x:Class="TaxiClient.Shell" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:Regions="clr-namespace:Microsoft.Practices.Prism.Regions;assembly=Microsoft.Practices.Prism" Title="Taxi" Height="370" Width="800"> <Grid Margin="2"> <ContentControl Regions:RegionManager.RegionName="MenuRegion" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" HorizontalContentAlignment="Stretch" VerticalContentAlignment="Stretch" />   <ContentControl Grid.Row="1" Regions:RegionManager.RegionName="MainRegion" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" HorizontalContentAlignment="Stretch" VerticalContentAlignment="Stretch" /> <!--<Border Grid.ColumnSpan="2" BorderThickness="2" CornerRadius="3" BorderBrush="LightBlue" />-->   </Grid> </Window> 4. Modules Prism provides the ability to build composite applications and modules play an important role in it. For example if you are building a Mortgage Loan Processor application with 3 components, i.e. customer’s credit history,  existing mortgages, new home/loan information; and consider that the customer’s credit history component involves gathering data about his/her address, background information, job details etc. The idea here using Prism modules is to separate the implementation of these 3 components into their own visual studio projects allowing to build components with no dependency on each other and independently. If we need to add another component to the application, the component can be developed by in house team or some other team in the organization by starting with a new Visual Studio project and adding to the solution at the run time with very little knowledge about the application. Prism modules are defined by implementing the IModule interface and each visual studio project to be considered as a module should implement the IModule interface.  From the BootStrapper.cs you shall observe that we are overriding the method by returning a ConfiguratingModuleCatalog which returns the modules that are registered for the application using the app.config file  and you can also add module using code. Lets take a look into configuration file.   <?xml version="1.0"?> <configuration> <configSections> <section name="modules" type="Microsoft.Practices.Prism.Modularity.ModulesConfigurationSection, Microsoft.Practices.Prism"/> </configSections> <modules> <module assemblyFile="TaxiModules.dll" moduleType="TaxiModules.ModuleInitializer, TaxiModules" moduleName="TaxiModules"/> </modules> </configuration> Here we are adding TaxiModules project to our solution and TaxiModules.ModuleInitializer implements IModule interface   5. Module Mapper With Prism modules you can dynamically add or remove modules from the regions, apart from that Prism also provides API to control adding/removing the views from a region within the same module. Taxi Information Screen: Engage the Taxi Screen: The sample application has two screens, ‘Taxi Information’ and ‘Engage the Taxi’ and they both reside in same module, TaxiModules. ‘Engage the Taxi’ is again made of two user controls, FareView on the left and TotalView on the right. We have created a Shell with two regions, MenuRegion and MainRegion with menu loaded into MenuRegion. We can create a wrapper user control called EngageTheTaxi made of FareView and TotalView and load either TaxiInfo or EngageTheTaxi into MainRegion based on the user action. Though it will work it tightly binds the user controls and for every combination of user controls, we need to create a dummy wrapper control to contain them. Instead we can apply the principles we learned so far from Shell/regions and introduce another template (LeftAndRightRegionView.xaml) made of two regions Region1 (left) and Region2 (right) and load  FareView and TotalView dynamically.  To help with loading of the views dynamically I have introduce an helper an interface, IInjectSingleViewService,  idea suggested by Mike Taulty, a must read blog for .Net developers. using System; using System.Collections.Generic; using System.ComponentModel;   namespace Framework.PresentationUtility.Navigation {   public interface IInjectSingleViewService : INotifyPropertyChanged { IEnumerable<CommandViewDefinition> Commands { get; } IEnumerable<ModuleViewDefinition> Modules { get; }   void RegisterViewForRegion(string commandName, string viewName, string regionName, Type viewType); void ClearViewFromRegion(string viewName, string regionName); void RegisterModule(string moduleName, IList<ModuleMapper> moduleMappers); } } The Interface declares three methods to work with views: RegisterViewForRegion: Registers a view with a particular region. You can register multiple views and their regions under one command.  When this particular command is invoked all the views registered under it will be loaded into their regions. ClearViewFromRegion: To unload a specific view from a region. RegisterModule: The idea is when a command is invoked you can load the UI with set of controls in their default position and based on the user interaction, you can load different contols in to different regions on the fly.  And it is supported ModuleViewDefinition and ModuleMappers as shown below. namespace Framework.PresentationUtility.Navigation { public class ModuleViewDefinition { public string ModuleName { get; set; } public IList<ModuleMapper> ModuleMappers; public ICommand Command { get; set; } }   public class ModuleMapper { public string ViewName { get; set; } public string RegionName { get; set; } public Type ViewType { get; set; } } } 6. Event Aggregator Prism event aggregator enables messaging between components as in Observable pattern, Notifier notifies the Observer which receives notification it is interested in. When it comes to Observable pattern, Observer has to unsubscribes for notifications when it no longer interested in notifications, which allows the Notifier to remove the Observer’s reference from it’s local cache. Though .Net has managed garbage collection it cannot remove inactive the instances referenced by an active instance resulting in memory leak, keeping the Observers in memory as long as Notifier stays in memory.  Developers have to be very careful to unsubscribe when necessary and it often gets overlooked, to overcome these problems Prism Event Aggregator uses weak references to cache the reference (Observer in this case)  and releases the reference (memory) once the instance goes out of scope. Using event aggregator is very simple, declare a generic type of CompositePresenationEvent by inheriting from it. using Microsoft.Practices.Prism.Events; using TaxiCommon.BAO;   namespace TaxiCommon.CompositeEvents { public class TaxiOnMoveEvent:CompositePresentationEvent<TaxiOnMove> { } }   TaxiOnMove.cs includes the properties which we want to exchange between the parties, FareView and TotalView. using System;   namespace TaxiCommon.BAO { public class TaxiOnMove { public TimeSpan MinutesAtTweleveMPH { get; set; } public double MilesAtSixMPH { get; set; } } }   Lets take a look into FareViewodel (Notifier) and how it raises the event.  Here we are raising the event by getting the event through GetEvent<..>() and publishing it with the payload private void OnAddMinutes(object obj) { TaxiOnMove payload = new TaxiOnMove(); if(MilesAtSixMPH != null) payload.MilesAtSixMPH = MilesAtSixMPH.Value; if(MinutesAtTweleveMPH != null) payload.MinutesAtTweleveMPH = new TimeSpan(0,0,MinutesAtTweleveMPH.Value,0);   _eventAggregator.GetEvent<TaxiOnMoveEvent>().Publish(payload); ResetMinutesAndMiles(); } And TotalViewModel(Observer) subscribes to notifications by getting the event through GetEvent<..>() namespace TaxiModules.ViewModels { public class TotalViewModel:ObservableBase { .... private IEventAggregator _eventAggregator;   public TotalViewModel(IEventAggregator eventAggregator) { _eventAggregator = eventAggregator; ... }   private void SubscribeToEvents() { _eventAggregator.GetEvent<TaxiStartedEvent>() .Subscribe(OnTaxiStarted, ThreadOption.UIThread,false,(filter) => true); _eventAggregator.GetEvent<TaxiOnMoveEvent>() .Subscribe(OnTaxiMove, ThreadOption.UIThread, false, (filter) => true); _eventAggregator.GetEvent<TaxiResetEvent>() .Subscribe(OnTaxiReset, ThreadOption.UIThread, false, (filter) => true); }   ... private void OnTaxiMove(TaxiOnMove taxiOnMove) { OnMoveFare fare = new OnMoveFare(taxiOnMove); Fares.Add(fare); SetTotalFare(new []{fare}); }   .... 7. MVVM through example In this section we are going to look into MVVM implementation through example.  I have all the modules declared in a single project, TaxiModules, again it is not necessary to have them into one project. Once the user logs into the application, will be greeted with the ‘Engage the Taxi’ screen which is made of two user controls, FareView.xaml and TotalView.Xaml. As you can see from the solution explorer, each of them have their own code behind files and  ViewModel classes, FareViewMode.cs, TotalViewModel.cs Lets take a look in to the FareView and how it interacts with FareViewModel using MVVM implementation. FareView.xaml acts as a view and FareViewMode.cs is it’s view model. The FareView code behind class   namespace TaxiModules.Views { /// <summary> /// Interaction logic for FareView.xaml /// </summary> public partial class FareView : UserControl { public FareView(FareViewModel viewModel) { InitializeComponent(); this.Loaded += (s, e) => { this.DataContext = viewModel; }; } } } The FareView is bound to FareViewModel through the data context  and you shall observe that DataContext is of type Object, i.e. the FareView doesn’t really know the type of ViewModel (FareViewModel). This helps separation of View and ViewModel as View and ViewModel are independent of each other, you can bind FareView to FareViewModel2 as well and the application compiles just fine. Lets take a look into FareView xaml file  <UserControl x:Class="TaxiModules.Views.FareView" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:Toolkit="clr-namespace:Microsoft.Windows.Controls;assembly=WPFToolkit" xmlns:Commands="clr-namespace:Microsoft.Practices.Prism.Commands;assembly=Microsoft.Practices.Prism"> <Grid Margin="10" > ....   <Border Style="{DynamicResource innerBorder}" Grid.Row="0" Grid.Column="0" Grid.RowSpan="11" Grid.ColumnSpan="2" Panel.ZIndex="1"/>   <Label Grid.Row="0" Content="Engage the Taxi" Style="{DynamicResource innerHeader}"/> <Label Grid.Row="1" Content="Select the State"/> <ComboBox Grid.Row="1" Grid.Column="1" ItemsSource="{Binding States}" Height="auto"> <ComboBox.ItemTemplate> <DataTemplate> <TextBlock Text="{Binding Name}"/> </DataTemplate> </ComboBox.ItemTemplate> <ComboBox.SelectedItem> <Binding Path="SelectedState" Mode="TwoWay"/> </ComboBox.SelectedItem> </ComboBox> <Label Grid.Row="2" Content="Select the Date of Entry"/> <Toolkit:DatePicker Grid.Row="2" Grid.Column="1" SelectedDate="{Binding DateOfEntry, ValidatesOnDataErrors=true}" /> <Label Grid.Row="3" Content="Enter time 24hr format"/> <TextBox Grid.Row="3" Grid.Column="1" Text="{Binding TimeOfEntry, TargetNullValue=''}"/> <Button Grid.Row="4" Grid.Column="1" Content="Start the Meter" Commands:Click.Command="{Binding StartMeterCommand}" />   <Label Grid.Row="5" Content="Run the Taxi" Style="{DynamicResource innerHeader}"/> <Label Grid.Row="6" Content="Number of Miles &lt;@6mph"/> <TextBox Grid.Row="6" Grid.Column="1" Text="{Binding MilesAtSixMPH, TargetNullValue='', ValidatesOnDataErrors=true}"/> <Label Grid.Row="7" Content="Number of Minutes @12mph"/> <TextBox Grid.Row="7" Grid.Column="1" Text="{Binding MinutesAtTweleveMPH, TargetNullValue=''}"/> <Button Grid.Row="8" Grid.Column="1" Content="Add Minutes and Miles " Commands:Click.Command="{Binding AddMinutesCommand}"/> <Label Grid.Row="9" Content="Other Operations" Style="{DynamicResource innerHeader}"/> <Button Grid.Row="10" Grid.Column="1" Content="Reset the Meter" Commands:Click.Command="{Binding ResetCommand}"/>   </Grid> </UserControl> The highlighted code from the above code shows data binding, for example ComboBox which displays list of states has it’s ItemsSource bound to States property, with DataTemplate bound to Name and SelectedItem  to SelectedState. You might be wondering what are all these properties and how it is able to bind to them.  The answer lies in data context, i.e., when you bound a control, WPF looks for data context on the root object (Grid in this case) and if it can’t find data context it will look into root’s root, i.e. FareView UserControl and it is bound to FareViewModel.  Each of those properties have be declared on the ViewModel for the View to bind correctly. To put simply, View is bound to ViewModel through data context of type object and every control that is bound on the View actually binds to the public property on the ViewModel. Lets look into the ViewModel code (the following code is not an exact copy of FareViewMode.cs, pasted relevant code for this section)   namespace TaxiModules.ViewModels { public class FareViewModel:ObservableBase, IDataErrorInfo { public List<USState> States { get { return USStates.StateList; } }   public USState SelectedState { get { return _selectedState; } set { _selectedState = value; RaisePropertyChanged(_selectedStatePropertyName); } }   public DateTime? DateOfEntry { get { return _dateOfEntry; } set { _dateOfEntry = value; RaisePropertyChanged(_dateOfEntryPropertyName); } }   public TimeSpan? TimeOfEntry { get { return _timeOfEntry; } set { _timeOfEntry = value; RaisePropertyChanged(_timeOfEntryPropertyName); } }   public double? MilesAtSixMPH { get { return _milesAtSixMPH; } set { _milesAtSixMPH = value; RaisePropertyChanged(_distanceAtSixMPHPropertyName); } }   public int? MinutesAtTweleveMPH { get { return _minutesAtTweleveMPH; } set { _minutesAtTweleveMPH = value; RaisePropertyChanged(_minutesAtTweleveMPHPropertyName); } }   public ICommand StartMeterCommand { get { if(_startMeterCommand == null) { _startMeterCommand = new DelegateCommand<object>(OnStartMeter, CanStartMeter); } return _startMeterCommand; } }   public ICommand AddMinutesCommand { get { if(_addMinutesCommand == null) { _addMinutesCommand = new DelegateCommand<object>(OnAddMinutes, CanAddMinutes); } return _addMinutesCommand; } }   public ICommand ResetCommand { get { if(_resetCommand == null) { _resetCommand = new DelegateCommand<object>(OnResetCommand); } return _resetCommand; } }   } private void OnStartMeter(object obj) { _eventAggregator.GetEvent<TaxiStartedEvent>().Publish( new TaxiStarted() { EngagedOn = DateOfEntry.Value.Date + TimeOfEntry.Value, EngagedState = SelectedState.Value });   _isMeterStarted = true; OnPropertyChanged(this,null); } And views communicate user actions like button clicks, tree view item selections, etc using commands. When user clicks on ‘Start the Meter’ button it invokes the method StartMeterCommand, which calls the method OnStartMeter which publishes the event to TotalViewModel using event aggregator  and TaxiStartedEvent. namespace TaxiModules.ViewModels { public class TotalViewModel:ObservableBase { ... private IEventAggregator _eventAggregator;   public TotalViewModel(IEventAggregator eventAggregator) { _eventAggregator = eventAggregator;   InitializePropertyNames(); InitializeModel(); SubscribeToEvents(); }   public decimal? TotalFare { get { return _totalFare; } set { _totalFare = value; RaisePropertyChanged(_totalFarePropertyName); } } .... private void SubscribeToEvents() { _eventAggregator.GetEvent<TaxiStartedEvent>().Subscribe(OnTaxiStarted, ThreadOption.UIThread,false,(filter) => true); _eventAggregator.GetEvent<TaxiOnMoveEvent>().Subscribe(OnTaxiMove, ThreadOption.UIThread, false, (filter) => true); _eventAggregator.GetEvent<TaxiResetEvent>().Subscribe(OnTaxiReset, ThreadOption.UIThread, false, (filter) => true); }   private void OnTaxiStarted(TaxiStarted taxiStarted) { Fares.Add(new EntryFare()); Fares.Add(new StateTaxFare(taxiStarted)); Fares.Add(new NightSurchargeFare(taxiStarted)); Fares.Add(new PeakHourWeekdayFare(taxiStarted));   SetTotalFare(Fares); }   private void SetTotalFare(IEnumerable<IFare> fares) { TotalFare = (_totalFare ?? 0) + TaxiFareHelper.GetTotalFare(fares); } ....   } }   TotalViewModel subscribes to events, TaxiStartedEvent and rest. When TaxiStartedEvent gets invoked it calls the OnTaxiStarted method which sets the total fare which includes entry fee, state tax, nightly surcharge, peak hour weekday fare.   Note that TotalViewModel derives from ObservableBase which implements the method RaisePropertyChanged which we are invoking in Set of TotalFare property, i.e, once we update the TotalFare property it raises an the event that  allows the TotalFare text box to fetch the new value through the data context. ViewModel is communicating with View through data context and it has no knowledge about View, helping in loose coupling of ViewModel and View.   I have attached the source code (.Net 4.0, Prism 4.0, VS 2010) , download and play with it and don’t forget to leave your comments.  

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• WPF MenuItem.Command binding to ElementName results to System.Windows.Data Error: 4 : Cannot find so

  - by e28Makaveli

  I have the following XAML: <UserControl x:Class="EMS.Controls.Dictionary.TOCControl" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:vm="clr-namespace:EMS.Controls.Dictionary.Models" xmlns:diagnostics="clr-namespace:System.Diagnostics;assembly=WindowsBase" x:Name="root" > <TreeView x:Name="TOCTreeView" Background="White" Padding="3,5" ContextMenuOpening="TOCTreeView_ContextMenuOpening" ItemsSource="{Binding Children}" BorderBrush="{x:Null}" > <TreeView.ItemTemplate> <HierarchicalDataTemplate ItemsSource="{Binding Path=Children, Mode=OneTime}"> <Grid > <Grid.ColumnDefinitions> <ColumnDefinition Width="Auto"/> <!--<ColumnDefinition Width="Auto"/>--> <ColumnDefinition Width="*"/> </Grid.ColumnDefinitions> <!--<CheckBox VerticalAlignment="Center" IsChecked="{Binding IsVisible}"/>--> <ContentPresenter Grid.Column="0" Height="16" Width="20" Content="{Binding LayerRepresentation}" /> <!--<ContentPresenter Grid.Column="1" > <ContentPresenter.Content> Test </ContentPresenter.Content> </ContentPresenter>--> <TextBlock Grid.Column="2" FontWeight="Normal" Text="{Binding Path=Alias, Mode=OneWay}" > <ToolTipService.ToolTip> <TextBlock Text="{Binding Description}" TextWrapping="Wrap"/> </ToolTipService.ToolTip> </TextBlock> </Grid> <HierarchicalDataTemplate.ItemTemplate> <HierarchicalDataTemplate ItemsSource="{Binding Path=Children, Mode=OneTime}"> <!--<DataTemplate>--> <Grid > <Grid.ColumnDefinitions> <ColumnDefinition Width="Auto"/> <ColumnDefinition Width="Auto"/> <ColumnDefinition Width="*"/> </Grid.ColumnDefinitions> <CheckBox VerticalAlignment="Center" IsChecked="{Binding IsVisible}"/> <ContentPresenter Grid.Column="1" Content="{Binding LayerRepresentation, Mode=OneWay}" /> <TextBlock Margin="0,1,0,1" Text="{Binding Path=Alias, Mode=OneWay}" Grid.Column="2"> <ToolTipService.ToolTip> <TextBlock Text="{Binding Description}" TextWrapping="Wrap"/> </ToolTipService.ToolTip> </TextBlock> </Grid> <!--</DataTemplate>--> </HierarchicalDataTemplate> </HierarchicalDataTemplate.ItemTemplate> </HierarchicalDataTemplate> </TreeView.ItemTemplate> <TreeView.ContextMenu> <ContextMenu> <MenuItem Name="miRemove" Header="Remove" Command="{Binding ElementName=root, Path=RemoveItemCmd, diagnostics:PresentationTraceSources.TraceLevel=High}"> <MenuItem.Icon> <Image Source="../images/16x16/Delete.png"/> </MenuItem.Icon> </MenuItem> <MenuItem Header="Properties" Command="{Binding ElementName=root, Path=GetItemPropertiesCmd}"/> </ContextMenu> </TreeView.ContextMenu> </TreeView> </UserControl> Code behind for this UserControl has two ICommand properties with names: RemoveItemCmd and GetItemPropertiesCmd. However, I get System.Windows.Data Error: 4 : Cannot find source for binding with reference 'ElementName=root'. BindingExpression:Path=RemoveItemCmd; DataItem=null; target element is 'MenuItem' (Name='miRemove'); target property is 'Command' (type 'ICommand') System.Windows.Data Error: 4 : Cannot find source for binding with reference 'ElementName=root'. BindingExpression:Path=GetItemPropertiesCmd; DataItem=null; target element is 'MenuItem' (Name=''); target property is 'Command' (type 'ICommand') when UserControl is constructed. Why is this and how do I resolve?

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• Enable button based on TextBox value (WPF)

  - by zendar

  This is MVVM application. There is a window and related view model class. There is TextBox, Button and ListBox on form. Button is bound to DelegateCommand that has CanExecute function. Idea is that user enters some data in text box, presses button and data is appended to list box. I would like to enable command (and button) when user enters correct data in TextBox. Things work like this now: CanExecute() method contains code that checks if data in property bound to text box is correct. Text box is bound to property in view model UpdateSourceTrigger is set to PropertyChanged and property in view model is updated after each key user presses. Problem is that CanExecute() does not fire when user enters data in text box. It doesn't fire even when text box lose focus. How could I make this work? Edit: Re Yanko's comment: Delegate command is implemented in MVVM toolkit template and when you create new MVVM project, there is Delegate command in solution. As much as I saw in Prism videos this should be the same class (or at least very similar). Here is XAML snippet: ... <UserControl.Resources> <views:CommandReference x:Key="AddObjectCommandReference" Command="{Binding AddObjectCommand}" /> </UserControl.Resources> ... <TextBox Text="{Binding ObjectName, UpdateSourceTrigger=PropertyChanged}"> </TextBox> <Button Command="{StaticResource AddObjectCommandReference}">Add</Button> ... View model: // Property bound to textbox public string ObjectName { get { return objectName; } set { objectName = value; OnPropertyChanged("ObjectName"); } } // Command bound to button public ICommand AddObjectCommand { get { if (addObjectCommand == null) { addObjectCommand = new DelegateCommand(AddObject, CanAddObject); } return addObjectCommand; } } private void AddObject() { if (ObjectName == null || ObjectName.Length == 0) return; objectNames.AddSourceFile(ObjectName); OnPropertyChanged("ObjectNames"); // refresh listbox } private bool CanAddObject() { return ObjectName != null && ObjectName.Length > 0; } As I wrote in the first part of question, following things work: property setter for ObjectName is triggered on every keypress in textbox if I put return true; in CanAddObject(), command is active (button to) It looks to me that binding is correct. Thing that I don't know is how to make CanExecute() fire in setter of ObjectName property from above code. Re Ben's and Abe's answers: CanExecuteChanged() is event handler and compiler complains: The event 'System.Windows.Input.ICommand.CanExecuteChanged' can only appear on the left hand side of += or -= there are only two more members of ICommand: Execute() and CanExecute() Do you have some example that shows how can I make command call CanExecute(). I found command manager helper class in DelegateCommand.cs and I'll look into it, maybe there is some mechanism that could help. Anyway, idea that in order to activate command based on user input, one needs to "nudge" command object in property setter code looks clumsy. It will introduce dependencies and one of big points of MVVM is reducing them. Is it possible to solve this problem by using dependency properties?

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• MVVM, ContextMenus and binding to ViewModel defined Command

  - by Simon Fox

  Hi I am having problems with the binding of a ContextMenu command to an ICommand property in my ViewModel. The binding seems to be attaching fine...i.e when I inspect the value of the ICommand property it is bound to an instance of RelayCommand. The CanExecute delegate does get invoked, however when I open the context menu and select an item the Execute delegate does not get invoked. Heres my View (which is defined as the DataTemplate to use for instances of the following ViewModel in a resource dictionary): <UserControl x:Class="SmartSystems.DragDropProto.ProductLinkView" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:local="clr-namespace:Proto"> <UserControl.Resources> <local:CenteringConverter x:Key="centeringConvertor"> </local:CenteringConverter> </UserControl.Resources> <UserControl.ContextMenu> <ContextMenu> <MenuItem Command="{Binding ChangeColor}">Change Color</MenuItem> </ContextMenu> </UserControl.ContextMenu> <Canvas> <Ellipse Width="5" Height="5" > <Ellipse.Fill> <SolidColorBrush Color="{Binding LinkColor}"></SolidColorBrush> </Ellipse.Fill> <Ellipse.RenderTransform> <TranslateTransform X="{Binding EndpointOneXPos, Converter={StaticResource centeringConvertor}}" Y="{Binding EndpointOneYPos, Converter={StaticResource centeringConvertor}}"/> </Ellipse.RenderTransform> </Ellipse> <Line X1="{Binding Path=EndpointOneXPos}" Y1="{Binding Path=EndpointOneYPos}" X2="{Binding Path=EndpointTwoXPos}" Y2="{Binding Path=EndpointTwoYPos}"> <Line.Stroke> <SolidColorBrush Color="{Binding LinkColor}"></SolidColorBrush> </Line.Stroke> </Line> <Ellipse Width="5" Height="5" > <Ellipse.Fill> <SolidColorBrush Color="{Binding LinkColor}"></SolidColorBrush> </Ellipse.Fill> <Ellipse.RenderTransform> <TranslateTransform X="{Binding EndpointTwoXPos, Converter={StaticResource centeringConvertor}}" Y="{Binding EndpointTwoYPos, Converter={StaticResource centeringConvertor}}"/> </Ellipse.RenderTransform> </Ellipse> </Canvas> </UserControl> and ViewModel (with uneccessary implementation details removed): class ProductLinkViewModel : BaseViewModel { public ICommand ChangeColor { get; private set; } public Color LinkColor { get; private set; } public ProductLinkViewModel(....) { ... ChangeColor = new RelayCommand(ChangeColorAction); LinkColor = Colors.Blue; } private void ChangeColorAction(object param) { LinkColor = LinkColor == Colors.Blue ? Colors.Red : Colors.Blue; OnPropertyChanged("LinkColor"); } }

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• Adventures in MVVM &ndash; My ViewModel Base

  - by Brian Genisio's House Of Bilz

  More Adventures in MVVM First, I’d like to say: THIS IS NOT A NEW MVVM FRAMEWORK. I tend to believe that MVVM support code should be specific to the system you are building and the developers working on it.  I have yet to find an MVVM framework that does everything I want it to without doing too much.  Don’t get me wrong… there are some good frameworks out there.  I just like to pick and choose things that make sense for me.  I’d also like to add that some of these features only work in WPF.  As of Silveright 4, they don’t support binding to dynamic properties, so some of the capabilities are lost. That being said, I want to share my ViewModel base class with the world.  I have had several conversations with people about the problems I have solved using this ViewModel base.  A while back, I posted an article about some experiments with a “Rails Inspired ViewModel”.  What followed from those ideas was a ViewModel base class that I take with me and use in my projects.  It has a lot of features, all designed to reduce the friction in writing view models. I have put the code out on Codeplex under the project: ViewModelSupport. Finally, this article focuses on the ViewModel and only glosses over the View and the Model.  Without all three, you don’t have MVVM.  But this base class is for the ViewModel, so that is what I am focusing on. Features: Automatic Command Plumbing Property Change Notification Strongly Typed Property Getter/Setters Dynamic Properties Default Property values Derived Properties Automatic Method Execution Command CanExecute Change Notification Design-Time Detection What about Silverlight? Automatic Command Plumbing This feature takes the plumbing out of creating commands.  The common pattern for commands in a ViewModel is to have an Execute method as well as an optional CanExecute method.  To plumb that together, you create an ICommand Property, and set it in the constructor like so: Before public class AutomaticCommandViewModel { public AutomaticCommandViewModel() { MyCommand = new DelegateCommand(Execute_MyCommand, CanExecute_MyCommand); } public void Execute_MyCommand() { // Do something } public bool CanExecute_MyCommand() { // Are we in a state to do something? return true; } public DelegateCommand MyCommand { get; private set; } } With the base class, this plumbing is automatic and the property (MyCommand of type ICommand) is created for you.  The base class uses the convention that methods be prefixed with Execute_ and CanExecute_ in order to be plumbed into commands with the property name after the prefix.  You are left to be expressive with your behavior without the plumbing.  If you are wondering how CanExecuteChanged is raised, see the later section “Command CanExecute Change Notification”. After public class AutomaticCommandViewModel : ViewModelBase { public void Execute_MyCommand() { // Do something } public bool CanExecute_MyCommand() { // Are we in a state to do something? return true; } }   Property Change Notification One thing that always kills me when implementing ViewModels is how to make properties that notify when they change (via the INotifyPropertyChanged interface).  There have been many attempts to make this more automatic.  My base class includes one option.  There are others, but I feel like this works best for me. The common pattern (without my base class) is to create a private backing store for the variable and specify a getter that returns the private field.  The setter will set the private field and fire an event that notifies the change, only if the value has changed. Before public class PropertyHelpersViewModel : INotifyPropertyChanged { private string text; public string Text { get { return text; } set { if(text != value) { text = value; RaisePropertyChanged("Text"); } } } protected void RaisePropertyChanged(string propertyName) { var handlers = PropertyChanged; if(handlers != null) handlers(this, new PropertyChangedEventArgs(propertyName)); } public event PropertyChangedEventHandler PropertyChanged; } This way of defining properties is error-prone and tedious.  Too much plumbing.  My base class eliminates much of that plumbing with the same functionality: After public class PropertyHelpersViewModel : ViewModelBase { public string Text { get { return Get<string>("Text"); } set { Set("Text", value);} } }   Strongly Typed Property Getters/Setters It turns out that we can do better than that.  We are using a strongly typed language where the use of “Magic Strings” is often frowned upon.  Lets make the names in the getters and setters strongly typed: A refinement public class PropertyHelpersViewModel : ViewModelBase { public string Text { get { return Get(() => Text); } set { Set(() => Text, value); } } }   Dynamic Properties In C# 4.0, we have the ability to program statically OR dynamically.  This base class lets us leverage the powerful dynamic capabilities in our ecosystem. (This is how the automatic commands are implemented, BTW)  By calling Set(“Foo”, 1), you have now created a dynamic property called Foo.  It can be bound against like any static property.  The opportunities are endless.  One great way to exploit this behavior is if you have a customizable view engine with templates that bind to properties defined by the user.  The base class just needs to create the dynamic properties at runtime from information in the model, and the custom template can bind even though the static properties do not exist. All dynamic properties still benefit from the notifiable capabilities that static properties do. For any nay-sayers out there that don’t like using the dynamic features of C#, just remember this: the act of binding the View to a ViewModel is dynamic already.  Why not exploit it?  Get over it :) Just declare the property dynamically public class DynamicPropertyViewModel : ViewModelBase { public DynamicPropertyViewModel() { Set("Foo", "Bar"); } } Then reference it normally <TextBlock Text="{Binding Foo}" />   Default Property Values The Get() method also allows for default properties to be set.  Don’t set them in the constructor.  Set them in the property and keep the related code together: public string Text { get { return Get(() => Text, "This is the default value"); } set { Set(() => Text, value);} }   Derived Properties This is something I blogged about a while back in more detail.  This feature came from the chaining of property notifications when one property affects the results of another, like this: Before public class DependantPropertiesViewModel : ViewModelBase { public double Score { get { return Get(() => Score); } set { Set(() => Score, value); RaisePropertyChanged("Percentage"); RaisePropertyChanged("Output"); } } public int Percentage { get { return (int)(100 * Score); } } public string Output { get { return "You scored " + Percentage + "%."; } } } The problem is: The setter for Score has to be responsible for notifying the world that Percentage and Output have also changed.  This, to me, is backwards.    It certainly violates the “Single Responsibility Principle.” I have been bitten in the rear more than once by problems created from code like this.  What we really want to do is invert the dependency.  Let the Percentage property declare that it changes when the Score Property changes. After public class DependantPropertiesViewModel : ViewModelBase { public double Score { get { return Get(() => Score); } set { Set(() => Score, value); } } [DependsUpon("Score")] public int Percentage { get { return (int)(100 * Score); } } [DependsUpon("Percentage")] public string Output { get { return "You scored " + Percentage + "%."; } } }   Automatic Method Execution This one is extremely similar to the previous, but it deals with method execution as opposed to property.  When you want to execute a method triggered by property changes, let the method declare the dependency instead of the other way around. Before public class DependantMethodsViewModel : ViewModelBase { public double Score { get { return Get(() => Score); } set { Set(() => Score, value); WhenScoreChanges(); } } public void WhenScoreChanges() { // Handle this case } } After public class DependantMethodsViewModel : ViewModelBase { public double Score { get { return Get(() => Score); } set { Set(() => Score, value); } } [DependsUpon("Score")] public void WhenScoreChanges() { // Handle this case } }   Command CanExecute Change Notification Back to Commands.  One of the responsibilities of commands that implement ICommand – it must fire an event declaring that CanExecute() needs to be re-evaluated.  I wanted to wait until we got past a few concepts before explaining this behavior.  You can use the same mechanism here to fire off the change.  In the CanExecute_ method, declare the property that it depends upon.  When that property changes, the command will fire a CanExecuteChanged event, telling the View to re-evaluate the state of the command.  The View will make appropriate adjustments, like disabling the button. DependsUpon works on CanExecute methods as well public class CanExecuteViewModel : ViewModelBase { public void Execute_MakeLower() { Output = Input.ToLower(); } [DependsUpon("Input")] public bool CanExecute_MakeLower() { return !string.IsNullOrWhiteSpace(Input); } public string Input { get { return Get(() => Input); } set { Set(() => Input, value);} } public string Output { get { return Get(() => Output); } set { Set(() => Output, value); } } }   Design-Time Detection If you want to add design-time data to your ViewModel, the base class has a property that lets you ask if you are in the designer.  You can then set some default values that let your designer see what things might look like in runtime. Use the IsInDesignMode property public DependantPropertiesViewModel() { if(IsInDesignMode) { Score = .5; } }   What About Silverlight? Some of the features in this base class only work in WPF.  As of version 4, Silverlight does not support binding to dynamic properties.  This, in my opinion, is a HUGE limitation.  Not only does it keep you from using many of the features in this ViewModel, it also keeps you from binding to ViewModels designed in IronRuby.  Does this mean that the base class will not work in Silverlight?  No.  Many of the features outlined in this article WILL work.  All of the property abstractions are functional, as long as you refer to them statically in the View.  This, of course, means that the automatic command hook-up doesn’t work in Silverlight.  You need to plumb it to a static property in order for the Silverlight View to bind to it.  Can I has a dynamic property in SL5?     Good to go? So, that concludes the feature explanation of my ViewModel base class.  Feel free to take it, fork it, whatever.  It is hosted on CodePlex.  When I find other useful additions, I will add them to the public repository.  I use this base class every day.  It is mature, and well tested.  If, however, you find any problems with it, please let me know!  Also, feel free to suggest patches to me via the CodePlex site.  :)

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• What&rsquo;s new in MVVM Light V3

  - by Laurent Bugnion

  V3 of the MVVM Light Toolkit was released during MIX10, after quite a long alpha stage. This post lists the new features in MVVM Light V3. Compatibility MVVM Light Toolkit V3 can be installed for the following tools and framework versions: Visual Studio 2008 SP1, Expression Blend 3 Windows Presentation Foundation 3.5 SP1 Silverlight 3 Visual Studio 2010 RC, Expression Blend 4 beta Windows Presentation Foundation 3.5 SP1 Windows Presentation Foundation 4 RC Silverlight 3 Silverlight 4 RC For more information about installing the MVVM Light Toolkit V3, please visit this page. For cleaning up existing installation, see this page. New in V3 RTM The following features have been added after V3 alpha3: Project template for the Windows Phone 7 series (Silverlight) This new template allows you to create a new MVVM Light application in Visual Studio 2010 RC and to run it in the Windows Phone 7 series emulator. This template uses the Silverlight 3 version of the MVVM Light Toolkit V3. At this time, only the essentials features of the GalaSoft.MvvmLight.dll assembly are supported on the phone. New in V3 alpha3 The following features have been added after V3 alpha2: New logo An awesome logo has been designed for MVVM Light by Philippe Schutz. DispatcherHelper class (in GalaSoft.MvvmLight.Extras.dll) This class is useful when you work on multi-threaded WPF or Silverlight applications. Initializing: The DispatcherHelper class must be initialized in the UI thread. For example, you can initialize the class in a Silverlight application’s Application_Startup event handler, or in the WPF application’s static App constructor (in App.xaml). // Initializing in Silverlight (in App.xaml) private void Application_Startup( object sender, StartupEventArgs e) { RootVisual = new MainPage(); DispatcherHelper.Initialize(); } // Initializing in WPF (in App.xaml) static App() { DispatcherHelper.Initialize(); } Verifying if a property exists The ViewModelBase.RaisePropertyChanged method now checks if a given property name exists on the ViewModel class, and throws an exception if that property cannot be found. This is useful to detect typos in a property name, for example during a refactoring. Note that the check is only done in DEBUG mode. Replacing IDisposable with ICleanup The IDisposable implementation in the ViewModelBase class has been marked obsolete. Instead, the ICleanup interface (and its Cleanup method) has been added. Implementing IDisposable in a ViewModel is still possible, but must be done explicitly. IDisposable in ViewModelBase was a bad practice, because it supposes that the ViewModel is garbage collected after Dispose is called. instead, the Cleanup method does not have such expectation. The ViewModelLocator class (created when an MVVM Light project template is used in Visual Studio or Expression Blend) exposes a static Cleanup method, which should in turn call each ViewModel’s Cleanup method. The ViewModel is free to override the Cleanup method if local cleanup must be performed. Passing EventArgs to command with EventToCommand The EventToCommand class is used to bind any event to an ICommand (typically on the ViewModel). In this case, it can be useful to pass the event’s EventArgs parameter to the command in the ViewModel. For example, for the MouseEnter event, you can pass the MouseEventArgs to a RelayCommand<MouseEventArgs> as shown in the next listings. Note: Bringing UI specific classes (such as EventArgs) into the ViewModel reduces the testability of the ViewModel, and thus should be used with care. Setting EventToCommand and PassEventArgsToCommand: <Grid x:Name="LayoutRoot"> <i:Interaction.Triggers> <i:EventTrigger EventName="MouseEnter"> <cmd:EventToCommand Command="{Binding MyCommand}" PassEventArgsToCommand="True" /> </i:EventTrigger> </i:Interaction.Triggers> </Grid> Getting the EventArgs in the command public RelayCommand<MouseEventArgs> MyCommand { get; private set; } public MainViewModel() { MyCommand = new RelayCommand<MouseEventArgs>(e => { // e is of type MouseEventArgs }); } Changes to templates Various changes have been made to project templates and item templates to make them more compatible with Silverlight 4 and to improve their visibility in Visual Studio and Expression Blend. Bug corrections When a message is sent through the Messenger class using the method Messenger.Default.Send<T>(T message, object token), and the token is a simple value (for example int), the message was not sent correctly. This bug is now corrected. New in V3 The following features have been added after V2. Sending messages with callback Certain classes have been added to the GalaSoft.MvvmLight.Messaging namespace, allowing sending a message and getting a callback from the recipient. These classes are: NotificationMessageWithCallback: Base class for messages with callback. NotificationMessageAction: A class with string notification, and a parameterless callback. NotificationMessageAction<T>: A class with string notification, and a callback with a parameter of type T. To send a message with callback, use the following code: var message = new NotificationMessageAction<bool>( "Hello world", callbackMessage => { // This is the callback code if (callbackMessage) { // ... } }); Messenger.Default.Send(message); To register and receive a message with callback, use the following code: Messenger.Default.Register<NotificationMessageAction<bool>>( this, message => { // Do something // Execute the callback message.Execute(true); }); Messenger.Default can be overriden The Messenger.Default property can also be replaced, for example for unit testing purposes, by using the Messenger.OverrideDefault method. All the public methods of the Messenger class have been made virtual, and can be overridden in the test messenger class. Sending messages to interfaces In V2, it was possible to deliver messages targeted to instances of a given class. in V3 it is still possible, but in addition you can deliver a message to instances that implement a certain interface. The message will not be delivered to other recipients. Use the overload Messenger.Default.Send<TMessage, TTarget>(TMessage message) where TTarget is, in fact, an interface (for example IDisposable). Of course the recipient must register to receive the type of message TMessage. Sending messages with a token Messages can now be sent through the Messenger with a token. To send a message with token, use the method overload Send<TMessage>(TMessage message, object token). To receive a message with token, use the methods Register<TMessage>(object recipient, object token, Action<TMessage> action) or Register<TMessage>(object recipient, object token, bool receiveDerivedMessagesToo, Action<TMessage> action) The token can be a simple value (int, string, etc…) or an instance of a class. The message is not delivered to recipients who registered with a different token, or with no token at all. Renaming CommandMessage to NotificationMessage To avoid confusion with ICommand and RelayCommand, the CommandMessage class has been renamed to NotificationMessage. This message class can be used to deliver a notification (of type string) to a recipient. ViewModelBase constructor with IMessenger The ViewModelBase class now accepts an IMessenger parameter. If this constructor is used instead of the default empty constructor, the IMessenger passed as parameter will be used to broadcast a PropertyChangedMessage when the method RaisePropertyChanged<T>(string propertyName, T oldValue, T newValue, bool broadcast) is used. In the default ViewModelBase constructor is used, the Messenger.Default instance will be used instead. EventToCommand behavior The EventToCommand behavior has been added in V3. It can be used to bind any event of any FrameworkElement to any ICommand (for example a RelayCommand located in the ViewModel). More information about the EventToCommand behavior can be found here and here. Updated the project templates to remove the sample application The project template has been updated to remove the sample application that was created every time that a new MVVM Light application was created in Visual Studio or Blend. This makes the creation of a new application easier, because you don’t need to remove code before you can start writing code. Bug corrections Some bugs that were in Version 2 have been corrected: In some occasions, an exception could be thrown when a recipient was registered for a message at the same time as a message was received. New names for DLLs If you upgrade an existing installation, you will need to change the reference to the DLLs in C:\Program Files\Laurent Bugnion (GalaSoft)\Mvvm Light Toolkit\Binaries. The assemblies have been moved, and the versions for Silverlight 4 and for WPF4 have been renamed, to avoid some confusion. It is now easier to make sure that you are using the correct DLL. WPF3.5SP1, Silverlight 3 When using the DLLs, make sure that you use the correct versions. WPF4, Silverlight 4 When using the DLLs, make sure that you use the correct versions.   Laurent Bugnion (GalaSoft) Subscribe | Twitter | Facebook | Flickr | LinkedIn

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• Changing the action of a hyperlink in a Silverlight RichTextArea

  - by Marc Schluper

  The title of this post could also have been "Move over Hyperlink, here comes Actionlink" or "Creating interactive text in Silverlight." But alas, there can be only one. Hyperlinks are very useful. However, they are also limited because their action is fixed: browse to a URL. This may have been adequate at the start of the Internet, but nowadays, in web applications, the one thing we do not want to happen is a complete change of context. In applications we typically like a hyperlink selection to initiate an action that updates a part of the screen. For instance, if my application has a map displayed with some text next to it, the map would react to a selection of a hyperlink in the text, e.g. by zooming in on a location and displaying additional locational information in a popup. In this way, the text becomes interactive text. It is quite common that one company creates and maintains websites for many client companies. To keep maintenance cost low, it is important that the content of these websites can be updated by the client companies themselves, without the need to involve a software engineer. To accommodate this scenario, we want the author of the interactive text to configure all hyperlinks (without writing any code). In a Silverlight RichTextArea, the default action of a Hyperlink is the same as a traditional hyperlink, but it can be changed: if the Command property has a value then upon a click event this command is called with the value of the CommandParameter as parameter. How can we let the author of the text specify a command for each hyperlink in the text, and how can we let an application react properly to a hyperlink selection event? We are talking about any command here. Obviously, the application would recognize only a specific set of commands, with well defined parameters, but the approach we take here is generic in the sense that it pertains to the RichTextArea and any command. So what do we require? We wish that: As a text author, I can configure the action of a hyperlink in a (rich) text without writing code; As a text author, I can persist the action of a hyperlink with the text; As a reader of persisted text, I can click a hyperlink and the configured action will happen; As an application developer, I can configure a control to use my application specific commands. In an excellent introduction to the RichTextArea, John Papa shows (among other things) how to persist a text created using this control. To meet our requirements, we can create a subclass of RichTextArea that uses John's code and allows plugging in two command specific components: one to prompt for a command definition, and one to execute the command. Since both of these plugins are application specific, our RichTextArea subclass should not assume anything about them except their interface. public interface IDefineCommand { void Prompt(string content, // the link content Action<string, object> callback); // the method called to convey the link definition } public interface IPerformCommand : ICommand {} The IDefineCommand plugin receives the content of the link (the text visible to the reader) and displays some kind of control that allows the author to define the link. When that's done, this (possibly changed) content string is conveyed back to the RichTextArea, together with an object that defines the command to execute when the link is clicked by the reader of the published text. The IPerformCommand plugin simply implements System.Windows.Input.ICommand. Let's use MEF to load the proper plugins. In the example solution there is a project that contains rudimentary implementations of these. The IDefineCommand plugin simply prompts for a command string (cf. a command line or query string), and the IPerformCommand plugin displays a MessageBox showing this command string. An actual application using this extended RichTextArea would have its own set of commands, each having their own parameters, and hence would provide more user friendly application specific plugins. Nonetheless, in any case a command can be persisted as a string and hence the two interfaces defined above suffice. For a Visual Studio 2010 solution, see my article on The Code Project.

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• Silverlight Cream for December 07, 2010 -- #1004

  - by Dave Campbell

  In this Issue: András Velvárt, Kunal Chowdhury(-2-), AvraShow, Gill Cleeren, Ian T. Lackey, Richard Waddell, Joe McBride, Michael Crump, Xpert360, keyboardP, and Pete Vickers(-2-). Above the Fold: Silverlight: "Grouping Records in Silverlight DataGrid using PagedCollectionView" Kunal Chowdhury WP7: "Phone 7 Back Button and the ListPicker control" Ian T. Lackey Shoutouts: Colin Eberhardt has some Silverlight 5 Adoption Predictions you may want to check out. Michael Crump has a post up showing lots of the goodness of Silverlight 5 from the Firestarter... screenshots, code snippets, etc: Silverlight 5 – What’s New? (Including Screenshots & Code Snippets) Kunal Chowdhury has a pretty complete Silverlight 5 feature set from the Firestarter and an embedded copy of Scott Guthrie's kenote running on the page: New Features Announced for Silverlight 5 Beta From SilverlightCream.com: Just how productive is WP7 development compared to iOS, Android and mobile Web? András Velvárt blogged about a contest he took part in to build a WP7 app in 1-1/2 hours without any prior knowledge of it's funtion. He and his team-mate were pitted against other teams on Android, IOS, and mobile Web... guess who got (almost) their entire app running? ... just too cool Andras! ... Grouping Records in Silverlight DataGrid using PagedCollectionView Kunal Chowdhury has a couple good posts up, this first one is on using the PagedCollectionView to group the records in a DataGrid... code included. Filtering Records in Silverlight DataGrid using PagedCollectionView Kunal Chowdhury then continues with another post on the PagedCollectionView only this time is showing how to do some filtering. DeepZoom Tips and Techniques AvraShow has a post up discussing using DeepZoom to explore, in his case, a Printed Circuit Board, with information about how he proceeded in doing that, and some tips and techniques along the way. The validation story in Silverlight (Part 2) Gill Cleeren has Part 2 of his Silverlight Validation series up at SilverlightShow. This post gets into IDataErrorInfo and INotifyDataErrorInfo. Lots of code and the example is available for download. Phone 7 Back Button and the ListPicker control Ian T. Lackey has a post up about the WP7 backbutton and what can get a failure from the Marketplace in that area, and how that applies to the ListPicker as well. Very Simple Example of ICommand CanExecute Method and CanExecuteChanged Event Richard Waddell has a nice detailed tutorial on ICommand and dealing with CanExecute... lots of Blend love in this post. Providing an Alternating Background Color for an ItemsControl Joe McBride has a post up discussing putting an alternating background color on an ItemsControl... you know, how you do on a grid... interesting idea, and all the code... Pimp my Silverlight Firestarter Michael Crump has a great Firestarter post up ... where and how to get the videos, the labs... a good Firestarter resource for sure. Adventures with PivotViewer Part 7: Slider control Xpert360 has part 7 of the PivotViewer series they're doing up. This time they're demonstrating taking programmatic control of the Zoom slider. Creating Transparent Lockscreen Wallpapers for WP7 I don't know keyboardP's name, but he's got a cool post up about getting an image up for the WP7 lock screen that has transparent regions on it... pretty cool actually. Windows Phone 7 Linq to XML 'strangeness' Pete Vickers has a post up describing a problem he found with Linq to XML on WP7. He even has a demo app that has the problem, and the fix... and it's all downloadable. Windows Phone 7 multi-line radio buttons Pete Vickers has another quick post up on radio buttons with so much text that it needs wrapping ... this is for WP7, but applies to Silverlight in general. Stay in the 'Light! Twitter SilverlightNews | Twitter WynApse | WynApse.com | Tagged Posts | SilverlightCream Join me @ SilverlightCream | Phoenix Silverlight User Group Technorati Tags: Silverlight    Silverlight 3    Silverlight 4    Windows Phone MIX10

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• Simple MVVM Walkthrough – Refactored

  - by Sean Feldman

  JR has put together a good introduction post into MVVM pattern. I love kick start examples that serve the purpose well. And even more than that I love examples that also can pass the real world projects check. So I took the sample code and refactored it slightly for a few aspects that a lot of developers might raise a brow. Michael has mentioned model (entity) visibility from view. I agree on that. A few other items that don’t settle are using property names as string (magical strings) and Saver class internal casting of a parameter (custom code for each Saver command). Fixing a property names usage is a straight forward exercise – leverage expressions. Something simple like this would do the initial job: class PropertyOf<T> { public static string Resolve(Expression<Func<T, object>> expression) { var member = expression.Body as MemberExpression; return member.Member.Name; } } With this, refactoring of properties names becomes an easy task, with confidence that an old property name string will not get left behind. An updated Invoice would look like this: public class Invoice : INotifyPropertyChanged { private int id; private string receiver; public event PropertyChangedEventHandler PropertyChanged; private void OnPropertyChanged(string propertyName) { if (PropertyChanged != null) { PropertyChanged(this, new PropertyChangedEventArgs(propertyName)); } } public int Id { get { return id; } set { if (id != value) { id = value; OnPropertyChanged(PropertyOf<Invoice>.Resolve(x => x.Id)); } } } public string Receiver { get { return receiver; } set { receiver = value; OnPropertyChanged(PropertyOf<Invoice>.Resolve(x => x.Receiver)); } } } For the saver, I decided to change it a little so now it becomes a “view-model agnostic” command, one that can be used for multiple commands/view-models. Updated Saver code now accepts an action at construction time and executes that action. No more black magic internal class Command : ICommand { private readonly Action executeAction; public Command(Action executeAction) { this.executeAction = executeAction; } public bool CanExecute(object parameter) { return true; } public event EventHandler CanExecuteChanged; public void Execute(object parameter) { // no more black magic executeAction(); } } Change in InvoiceViewModel is instantiation of Saver command and execution action for the specific command. public ICommand SaveCommand { get { if (saveCommand == null) saveCommand = new Command(ExecuteAction); return saveCommand; } set { saveCommand = value; } } private void ExecuteAction() { DisplayMessage = string.Format("Thanks for creating invoice: {0} {1}", Invoice.Id, Invoice.Receiver); } This way internal knowledge of InvoiceViewModel remains in InvoiceViewModel and Command (ex-Saver) is view-model agnostic. Now the sample is not only a good introduction, but also has some practicality in it. My 5 cents on the subject. Sample code MvvmSimple2.zip

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• MVVM Light Toolkit - RelayCommands, DelegateCommands, and ObservableObjects

  - by DanM

  I just started experimenting with Laurent Bugnion's MVVM Light Toolkit. I think I'm going to really like it, but I have a couple questions. Before I get to them, I need to explain where I'm coming from. I currently use a combination of Josh Smith's MVVM Foundation and another project on Codeplex called MVVM Toolkit. I use ObservableObject and Messenger from MVVM Foundation and DelegateCommand and CommandReference from MVVM Toolkit. The only real overlap between MVVM Foundation and MVVM Tookit is that they both have an implementation for ICommand: MVVM Foundation has a RelayCommand and MVVM Tookit has a DelegateCommand. Of these two, DelegateCommand appears to be more sophisticated. It employs a CommandManagerHelper that uses weak references to avoid memory leaks. With that said, a couple questions: Why does MVVM Light Toolkit use RelayCommand rather than DelegateCommand? Is the use of weak references in an ICommand unnecessary or not recommended for some reason? Why is there no ObservableObject in MVVM Light? ObservableObject is basically just the part of ViewModelBase that implements INotifyPropertyChanged, but it's very convenient to have as a separate class because view-models are not the only objects that need to implement INotifyPropertyChanged. For example, let's say you have DataGrid that binds to a list of Person objects. If any of the properties in Person can change while the user is viewing the DataGrid, Person would need to implement INotifyPropertyChanged. (I realize that if Person is auto-generated using something like LinqToSql, it will probably already implement INotifyPropertyChanged, but there are cases where I need to make a view-specific version of entity model objects, say, because I need to include a command to support a button column in a DataGrid.) Thanks.

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