concrete syntax tree - Page 357

Mocking HtmlHelper throws NullReferenceException

- by Matt Austin

I know that there are a few questions on StackOverflow on this topic but I haven't been able to get any of the suggestions to work for me. I've been banging my head against this for two days now so its time to ask for help... The following code snippit is a simplified unit test to demonstrate what I'm trying to do, which is basically call RadioButtonFor in the Microsoft.Web.Mvc assembly in a unit test. var model = new SendMessageModel { SendMessageType = SendMessageType.Member }; var vd = new ViewDataDictionary(model); vd.TemplateInfo = new TemplateInfo { HtmlFieldPrefix = string.Empty }; var controllerContext = new ControllerContext(new Mock<HttpContextBase>().Object, new RouteData(), new Mock<ControllerBase>().Object); var viewContext = new Mock<ViewContext>(new object[] { controllerContext, new Mock<IView>().Object, vd, new TempDataDictionary(), new Mock<TextWriter>().Object }); viewContext.Setup(v => v.View).Returns(new Mock<IView>().Object); viewContext.Setup(v => v.ViewData).Returns(vd).Callback(() => {throw new Exception("ViewData extracted");}); viewContext.Setup(v => v.TempData).Returns(new TempDataDictionary()); viewContext.Setup(v => v.Writer).Returns(new Mock<TextWriter>().Object); viewContext.Setup(v => v.RouteData).Returns(new RouteData()); viewContext.Setup(v => v.HttpContext).Returns(new Mock<HttpContextBase>().Object); viewContext.Setup(v => v.Controller).Returns(new Mock<ControllerBase>().Object); viewContext.Setup(v => v.FormContext).Returns(new FormContext()); var mockContainer = new Mock<IViewDataContainer>(); mockContainer.Setup(x => x.ViewData).Returns(vd); var helper = new HtmlHelper<ISendMessageModel>(viewContext.Object, mockContainer.Object, new RouteCollection()); helper.RadioButtonFor(m => m.SendMessageType, "Member", cssClass: "selector"); If I remove the cssClass parameter then the code works ok but fails consistently when adding additional parameters. I've tried every combination of mocking, instantiating concrete types and using fakes that I can think off but I always get a NullReferenceException when I call RadioButtonFor. Any help hugely appreciated!!

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How the simples GUI countdown is supposed to work?

- by Roman

I am trying to write the simples GUI countdown. I found in Internet some code but it is already too fancy for me. I am trying to keep it as simple as possible. So, I just want to have a window saying "You have 10 second left". The number of second should decrease every second from 10 to 0. I wrote a code. And I think I am close to the working solution. But I still missing something. Could you pleas help me to find out what is wrong? Here is my code: import javax.swing.*; public class Countdown { static JLabel label; // Method which defines the appearance of the window. private static void showGUI() { JFrame frame = new JFrame("Simple Countdown"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); JLabel label = new JLabel("Some Text"); frame.add(label); frame.pack(); frame.setVisible(true); } // Define a new thread in which the countdown is counting down. static Thread counter = new Thread() { public void run() { for (int i=10; i>0; i=i-1) { updateGUI(i,label); try {Thread.sleep(1000);} catch(InterruptedException e) {}; } } }; // A method which updates GUI (sets a new value of JLabel). private static void updateGUI(final int i, final JLabel label) { SwingUtilities.invokeLater(new Runnable(i,label) { public Runnable(int i, JLabel label) { this.i = i; this.label = label; } public void run() { label.setText("You have " + i + " seconds."); } }); } // The main method (entry point). public static void main(String[] args) { javax.swing.SwingUtilities.invokeLater(new Runnable() { public void run() { showGUI(); //counter.start(); } }); //counter.start(); } } And I have several concrete question about this code: Where should I place the counter.start();? (In my code I put it on 2 places. Which one is correct?) Why compiler complains about the constructor for Runnable? It says that I have an invalid method declaration and I need to specify the returned type. ADDED: I made the suggested corrections. And then I execute the code and get: Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException at Worker.run(Worker.java:12) In the Worker.java in the line 12 I have: label.setText("You have " + i + " seconds.");.

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How do I recover from an unchecked exception?

- by erickson

Unchecked exceptions are alright if you want to handle every failure the same way, for example by logging it and skipping to the next request, displaying a message to the user and handling the next event, etc. If this is my use case, all I have to do is catch some general exception type at a high level in my system, and handle everything the same way. But I want to recover from specific problems, and I'm not sure the best way to approach it with unchecked exceptions. Here is a concrete example. Suppose I have a web application, built using Struts2 and Hibernate. If an exception bubbles up to my "action", I log it, and display a pretty apology to the user. But one of the functions of my web application is creating new user accounts, that require a unique user name. If a user picks a name that already exists, Hibernate throws an org.hibernate.exception.ConstraintViolationException (an unchecked exception) down in the guts of my system. I'd really like to recover from this particular problem by asking the user to choose another user name, rather than giving them the same "we logged your problem but for now you're hosed" message. Here are a few points to consider: There a lot of people creating accounts simultaneously. I don't want to lock the whole user table between a "SELECT" to see if the name exists and an "INSERT" if it doesn't. In the case of relational databases, there might be some tricks to work around this, but what I'm really interested in is the general case where pre-checking for an exception won't work because of a fundamental race condition. Same thing could apply to looking for a file on the file system, etc. Given my CTO's propensity for drive-by management induced by reading technology columns in "Inc.", I need a layer of indirection around the persistence mechanism so that I can throw out Hibernate and use Kodo, or whatever, without changing anything except the lowest layer of persistence code. As a matter of fact, there are several such layers of abstraction in my system. How can I prevent them from leaking in spite of unchecked exceptions? One of the declaimed weaknesses of checked exceptions is having to "handle" them in every call on the stack—either by declaring that a calling method throws them, or by catching them and handling them. Handling them often means wrapping them in another checked exception of a type appropriate to the level of abstraction. So, for example, in checked-exception land, a file-system–based implementation of my UserRegistry might catch IOException, while a database implementation would catch SQLException, but both would throw a UserNotFoundException that hides the underlying implementation. How do I take advantage of unchecked exceptions, sparing myself of the burden of this wrapping at each layer, without leaking implementation details?

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Who calls the Destructor of the class when operator delete is used in multiple inheritance.

- by dicaprio-leonard

This question may sound too silly, however , I don't find concrete answer any where else. With little knowledge on how late binding works and virtual keyword used in inheritance. As in the code sample, when in case of inheritance where a base class pointer pointing to a derived class object created on heap and delete operator is used to deallocate the memory , the destructor of the of the derived and base will be called in order only when the base destructor is declared virtual function. Now my question is : 1) When the destructor of base is not virtual, why the problem of not calling derived dtor occur only when in case of using "delete" operator , why not in the case given below: derived drvd; base *bPtr; bPtr = &drvd; //DTOR called in proper order when goes out of scope. 2) When "delete" operator is used, who is reponsible to call the destructor of the class? The operator delete will have an implementation to call the DTOR ? or complier writes some extra stuff ? If the operator has the implementation then how does it looks like , [I need sample code how this would have been implemented]. 3) If virtual keyword is used in this example, how does operator delete now know which DTOR to call? Fundamentaly i want to know who calls the dtor of the class when delete is used. Sample Code class base { public: base() { cout<<"Base CTOR called"<<endl; } virtual ~base() { cout<<"Base DTOR called"<<endl; } }; class derived:public base { public: derived() { cout<<"Derived CTOR called"<<endl; } ~derived() { cout<<"Derived DTOR called"<<endl; } }; I'm not sure if this is a duplicate, I couldn't find in search. int main() { base *bPtr = new derived(); delete bPtr;// only when you explicitly try to delete an object return 0; }

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How to check for palindrome using Python logic

- by DrOnline

My background is only a 6 month college class in basic C/C++, and I'm trying to convert to Python. I may be talking nonsense, but it seems to me C, at least at my level, is very for-loop intensive. I solve most problems with these loops. And it seems to me the biggest mistake people do when going from C to Python is trying to implement C logic using Python, which makes things run slowly, and it's just not making the most of the language. I see on this website: http://hyperpolyglot.org/scripting (serach for "c-style for", that Python doesn't have C-style for loops. Might be outdated, but I interpret it to mean Python has its own methods for this. I've tried looking around, I can't find much up to date (Python 3) advice for this. How can I solve a palindrome challenge in Python, without using the for loop? I've done this in C in class, but I want to do it in Python, on a personal basis. The problem is from the Euler Project, great site btw. def isPalindrome(n): lst = [int(n) for n in str(n)] l=len(lst) if l==0 || l==1: return True elif len(lst)%2==0: for k in range (l) ##### else: while (k<=((l-1)/2)): if (list[]): ##### for i in range (999, 100, -1): for j in range (999,100, -1): if isPalindrome(i*j): print(i*j) break I'm missing a lot of code here. The five hashes are just reminders for myself. Concrete questions: 1) In C, I would make a for loop comparing index 0 to index max, and then index 0+1 with max-1, until something something. How to best do this in Python? 2) My for loop (in in range (999, 100, -1), is this a bad way to do it in Python? 3) Does anybody have any good advice, or good websites or resources for people in my position? I'm not a programmer, I don't aspire to be one, I just want to learn enough so that when I write my bachelor's degree thesis (electrical engineering), I don't have to simultaneously LEARN an applicable programming language while trying to obtain good results in the project. "How to go from basic C to great application of Python", that sort of thing. 4) Any specific bits of code to make a great solution to this problem would also be appreciated, I need to learn good algorithms.. I am envisioning 3 situations. If the value is zero or single digit, if it is of odd length, and if it is of even length. I was planning to write for loops... PS: The problem is: Find the highest value product of two 3 digit integers that is also a palindrome.

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XML Schema for a .NET type that inherits and implements

- by John Ruiz

Hi, Please consider the following three .NET types: I have an interface, an abstract class, and a concrete class. My question is how to write the XML Schema to include the properties from the interface and from the abstract class. public interface IStartable { bool RequiresKey { get; set; } void Start(object key); } public abstract class Vehicle { uint WheelCount { get; set; } } public class Car : Vehicle, IStartable { public bool RequiresKey { get; set; } public string Make { get; set; } publilc string Model { get; set; } public Car() {} public void Start(object key) { // start car with key } } I don't know how to complete this schema: <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" targetNamespace="cars" xmlns="cars" xmlns:c="cars">  <xs:element name="Car" type="c:Car" /> <xs:complexType name="Car"> <xs:complexContent> <xs:extension base="c:Vehicle"> <xs:group ref=c:CarGroup" /> </xs:extension> </xs:complexContent> </xs:complexType> <xs:group name="CarGroup"> <xs:sequence> <xs:element name="Make" type="xs:token" /> <xs:element name="Model" type="xs:token" /> </xs:sequence> </xs:group> <xs:complexType name="Vehicle"> <xs:sequence> <xs:element name="WheelCount" type="xs:unsignedInt" /> </xs:sequence> </xs:complexType> <xs:complexType name="IStartable"> <xs:sequence> <xs:element name="RequiresKey" type="xs:boolean" /> </xs:sequence> </xs:complexType> </xs:schema>

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Deriving from a component and implementing IDisposable properly

- by PaulH

I have a Visual Studio 2008 C# .NET 2.0 CF project with an abstract class derived from Component. From that class, I derive several concrete classes (as in my example below). But, when I go to exit my Form, though the Form's Dispose() member is called and components.Dispose() is called, my components are never disposed. Can anybody suggest how I can fix this design? public abstract class SomeDisposableComponentBase : Component { private System.ComponentModel.IContainer components; protected SomeDisposableComponentBase() { Initializecomponent(); } protected SomeDisposableComponentBase(IContainer container) { container.Add(this); Initializecomponent(); } private void InitializeComponent() { components = new System.ComponentModel.Container(); } protected abstract void Foo(); #region IDisposable Members bool disposed_; /// Warning 60 CA1063 : Microsoft.Design : Ensure that 'SomeDisposableComponentBase.Dispose()' is declared as public and sealed.* public void Dispose() { // never called Dispose(true); GC.SuppressFinalize(this); } protected virtual void Dispose(bool disposing) { // never called if (!disposed_) { if (disposing && (components != null)) { components.Dispose(); } disposed_ = true; } base.Dispose(disposing); } #endregion } public SomeDisposableComponent : SomeDisposableComponentBase { public SomeDisposableComponent() : base() { } public SomeDisposableComponent(IContainer container) : base(container) { } protected override void Foo() { // Do something... } protected override void Dispose(bool disposing) { // never called base.Dispose(disposing); } } public partial class my_form : Form { private SomeDisposableComponentBase d_; public my_form() { InitializeComponent(); if (null == components) components = new System.ComponentModel.Container(); d_ = new SomeDisposableComponent(components); } /// exit button clicked private void Exit_Click(object sender, EventArgs e) { this.Close(); } /// from the my_form.designer.cs protected override void Dispose(bool disposing) { if (disposing && (components != null)) { // this function is executed as expected when the form is closed components.Dispose(); } base.Dispose(disposing); } } *I note that FX-Cop is giving me a hint here. But, if I try to declare that function as sealed, I get the error: error CS0238: 'SomeDisposableComponentBase.Dispose()' cannot be sealed because it is not an override Declaring that function an override leads to: 'SomeDisposableComponentBase.Dispose()': cannot override inherited member 'System.ComponentModel.Component.Dispose()' because it is not marked virtual, abstract, or override Thanks, PaulH

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How to perform duplicate key validation using entlib (or DataAnnotations), MVC, and Repository pattern

- by olivehour

I have a set of ASP.NET 4 projects that culminate in an MVC (3 RC2) app. The solution uses Unity and EntLib Validation for cross-cutting dependency injection and validation. Both are working great for injecting repository and service layer implementations. However, I can't figure out how to do duplicate key validation. For example, when a user registers, we want to make sure they don't pick a UserID that someone else is already using. For this type of validation, the validating object must have a repository reference... or some other way to get an IQueryable / IEnumerable reference to check against other rows already in the DB. What I have is a UserMetadata class that has all of the property setters and getters for a user, along with all of the appropriate DataAnnotations and EntLib Validation attributes. There is also a UserEntity class implemented using EF4 POCO Entity Generator templates. The UserEntity depends on UserMetadata, because it has a MetadataTypeAttribute. I also have a UserViewModel class that has the same exact MetadataType attribute. This way, I can apply the same validation rules, via attributes, to both the entity and viewmodel. There are no concrete references to the Repository classes whatsoever. All repositories are injected using Unity. There is also a service layer that gets dependency injection. In the MVC project, service layer implementation classes are injected into the Controller classes (the controller classes only contain service layer interface references). Unity then injects the Repository implementations into the service layer classes (service classes also only contain interface references). I've experimented with the DataAnnotations CustomValidationAttribute in the metadata class. The problem with this is the validation method must be static, and the method cannot instantiate a repository implementation directly. My repository interface is IRepository, and I have only one single repository implementation class defined as EntityRepository for all domain objects. To instantiate a repository explicitly I would need to say new EntityRepository(), which would result in a circular dependency graph: UserMetadata [depends on] DuplicateUserIDValidator [depends on] UserEntity [depends on] UserMetadata. I've also tried creating a custom EntLib Validator along with a custom validation attribute. Here I don't have the same problem with a static method. I think I could get this to work if I could just figure out how to make Unity inject my EntityRepository into the validator class... which I can't. Right now, all of the validation code is in my Metadata class library, since that's where the custom validation attribute would go. Any ideas on how to perform validations that need to check against the current repository state? Can Unity be used to inject a dependency into a lower-layer class library?

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How to get started with testing(jMock)

- by London

Hello, I'm trying to learn how to write tests. I'm also learning Java, I was told I should learn/use/practice jMock, I've found some articles online that help to certain extend like : http://www.theserverside.com/news/1365050/Using-JMock-in-Test-Driven-Development http://jeantessier.com/SoftwareEngineering/Mocking.html#jMock And most articles I found was about test driven development, write tests first then write code to make the test pass. I'm not looking for that at the moment, I'm trying to write tests for already existing code with jMock. The official documentation is vague to say the least and just too hard for me. Does anybody have better way to learn this. Good books/links/tutorials would help me a lot. thank you EDIT - more concrete question : http://jeantessier.com/SoftwareEngineering/Mocking.html#jMock - from this article Tried this to mock this simple class : import java.util.Map; public class Cache { private Map<Integer, String> underlyingStorage; public Cache(Map<Integer, String> underlyingStorage) { this.underlyingStorage = underlyingStorage; } public String get(int key) { return underlyingStorage.get(key); } public void add(int key, String value) { underlyingStorage.put(key, value); } public void remove(int key) { underlyingStorage.remove(key); } public int size() { return underlyingStorage.size(); } public void clear() { underlyingStorage.clear(); } } Here is how I tried to create a test/mock : public class CacheTest extends TestCase { private Mockery context; private Map mockMap; private Cache cache; @Override @Before public void setUp() { context = new Mockery() { { setImposteriser(ClassImposteriser.INSTANCE); } }; mockMap = context.mock(Map.class); cache = new Cache(mockMap); } public void testCache() { context.checking(new Expectations() {{ atLeast(1).of(mockMap).size(); will(returnValue(int.class)); }}); } } It passes the test and basically does nothing, what I wanted is to create a map and check its size, and you know work some variations try to get a grip on this. Understand better trough examples, what else could I test here or any other exercises would help me a lot. tnx

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Data not synchornizing java sockets

- by Droid_Interceptor

I am writing a auction server and client and using a class called BidHandler to deal with the bids another class AuctionItem to deal with the items for auction. The main problem I am having is little synchroization problem. Screen output of client server as can see from the image at 1st it takes the new bid and changes the value of the time to it, but when one the user enters 1.0 the item seems to be changed to that. But later on when the bid changes again to 15.0 it seems to stay at that price. Is there any reason for that. I have included my code below. Sorry if didnt explain this well. This is the auction client import java.io.*; import java.net.*; public class AuctionClient { private AuctionGui gui; private Socket socket; private DataInputStream dataIn; private DataOutputStream dataOut; //Auction Client constructor String name used as identifier for each client to allow server to pick the winning bidder public AuctionClient(String name,String server, int port) { gui = new AuctionGui("Bidomatic 5000"); gui.input.addKeyListener (new EnterListener(this,gui)); gui.addWindowListener(new ExitListener(this)); try { socket = new Socket(server, port); dataIn = new DataInputStream(socket.getInputStream()); dataOut = new DataOutputStream(socket.getOutputStream()); dataOut.writeUTF(name); while (true) { gui.output.append("\n"+dataIn.readUTF()); } } catch (Exception e) { e.printStackTrace(); } } public void sentBid(String bid) { try { dataOut.writeUTF(bid); } catch(IOException e) { e.printStackTrace(); } } public void disconnect() { try { socket.close(); } catch(IOException e) { e.printStackTrace(); } } public static void main (String args[]) throws IOException { if(args.length!=3) { throw new RuntimeException ("Syntax: java AuctionClient <name> <serverhost> <port>"); } int port = Integer.parseInt(args[2]); AuctionClient a = new AuctionClient(args[0],args[1],port); } } The Auction Server import java.io.*; import java.net.*; import java.util.*; public class AuctionServer { public AuctionServer(int port) throws IOException { ServerSocket server = new ServerSocket(port); while(true) { Socket client = server.accept(); DataInputStream in = new DataInputStream(client.getInputStream()); String name = in.readUTF(); System.out.println("New client "+name+" from " +client.getInetAddress()); BidHandler b = new BidHandler (name, client); b.start(); } } public static void main(String args[]) throws IOException { if(args.length != 1) throw new RuntimeException("Syntax: java AuctionServer <port>"); new AuctionServer(Integer.parseInt(args[0])); } } The BidHandler import java.net.*; import java.io.*; import java.util.*; import java.lang.Float; public class BidHandler extends Thread { Socket socket; DataInputStream in; DataOutputStream out; String name; float currentBid = 0.0f; AuctionItem paper = new AuctionItem(" News Paper ", " Free newspaper from 1990 ", 1.0f, false); protected static Vector handlers = new Vector(); public BidHandler(String name, Socket socket) throws IOException { this.name = name; this.socket = socket; in = new DataInputStream (new BufferedInputStream (socket.getInputStream())); out = new DataOutputStream(new BufferedOutputStream(socket.getOutputStream())); } public synchronized void run() { try { broadcast("New bidder has entered the room"); handlers.addElement(this); while(true) { broadcast(paper.getName() + paper.getDescription()+" for sale at: " +paper.getPrice()); while(paper.getStatus() == false) { String message = in.readUTF(); currentBid = Float.parseFloat(message); broadcast("Bidder entered " +currentBid); if(currentBid > paper.getPrice()) { paper.setPrice(currentBid); broadcast("New Higgest Bid is "+paper.getPrice()); } else if(currentBid < paper.getPrice()) { broadcast("Higgest Bid is "+paper.getPrice()); } else if(currentBid == paper.getPrice()) { broadcast("Higgest Bid is "+paper.getPrice()); } } } } catch(IOException ex) { System.out.println("-- Connection to user lost."); } finally { handlers.removeElement(this); broadcast(name+" left"); try { socket.close(); } catch(IOException ex) { System.out.println("-- Socket to user already closed ?"); } } } protected static void broadcast (String message) { synchronized(handlers) { Enumeration e = handlers.elements(); while(e.hasMoreElements()) { BidHandler handler = (BidHandler) e.nextElement(); try { handler.out.writeUTF(message); handler.out.flush(); } catch(IOException ex) { handler = null; } } } } } The AuctionItem Class class AuctionItem { String itemName; String itemDescription; float itemPrice; boolean itemStatus; //Create a new auction item with name, description, price and status public AuctionItem(String name, String description, float price, boolean status) { itemName = name; itemDescription = description; itemPrice = price; itemStatus = status; } //return the price of the item. public synchronized float getPrice() { return itemPrice; } //Set the price of the item. public synchronized void setPrice(float newPrice) { itemPrice = newPrice; } //Get the status of the item public synchronized boolean getStatus() { return itemStatus; } //Set the status of the item public synchronized void setStatus(boolean newStatus) { itemStatus = newStatus; } //Get the name of the item public String getName() { return itemName; } //Get the description of the item public String getDescription() { return itemDescription; } } There is also simple GUI to go with this that seems to be working fine. If anyone wants it will include the GUI code.

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Why doesn't TextBlock databinding call ToString() on a property whose compile-time type is an interf

- by Jay

This started with weird behaviour that I thought was tied to my implementation of ToString(), and I asked this question: http://stackoverflow.com/questions/2916068/why-wont-wpf-databindings-show-text-when-tostring-has-a-collaborating-object It turns out to have nothing to do with collaborators and is reproducible. When I bind Label.Content to a property of the DataContext that is declared as an interface type, ToString() is called on the runtime object and the label displays the result. When I bind TextBlock.Text to the same property, ToString() is never called and nothing is displayed. But, if I change the declared property to a concrete implementation of the interface, it works as expected. Is this somehow by design? If so, any idea why? To reproduce: Create a new WPF Application (.NET 3.5 SP1) Add the following classes: public interface IFoo { string foo_part1 { get; set; } string foo_part2 { get; set; } } public class Foo : IFoo { public string foo_part1 { get; set; } public string foo_part2 { get; set; } public override string ToString() { return foo_part1 + " - " + foo_part2; } } public class Bar { public IFoo foo { get { return new Foo {foo_part1 = "first", foo_part2 = "second"}; } } } Set the XAML of Window1 to: <Window x:Class="WpfApplication1.Window1" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="Window1" Height="300" Width="300"> <StackPanel> <Label Content="{Binding foo, Mode=Default}"/> <TextBlock Text="{Binding foo, Mode=Default}"/> </StackPanel> </Window> in Window1.xaml.cs: public partial class Window1 : Window { public Window1() { InitializeComponent(); DataContext = new Bar(); } } When you run this application, you'll see the text only once (at the top, in the label). If you change the type of foo property on Bar class to Foo (instead of IFoo) and run the application again, you'll see the text in both controls.

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One Controller is Sometimes Bound Twice with Ninject

- by Dusda

I have the following NinjectModule, where we bind our repositories and business objects: /// <summary> /// Used by Ninject to bind interface contracts to concrete types. /// </summary> public class ServiceModule : NinjectModule { /// <summary> /// Loads this instance. /// </summary> public override void Load() { //bindings here. //Bind<IMyInterface>().To<MyImplementation>(); Bind<IUserRepository>().To<SqlUserRepository>(); Bind<IHomeRepository>().To<SqlHomeRepository>(); Bind<IPhotoRepository>().To<SqlPhotoRepository>(); //and so on //business objects Bind<IUser>().To<Data.User>(); Bind<IHome>().To<Data.Home>(); Bind<IPhoto>().To<Data.Photo>(); //and so on } } And here are the relevant overrides from our Global.asax, where we inherit from NinjectHttpApplication in order to integrate it with Asp.Net Mvc (The module lies in a separate dll called Thing.Web.Configuration): protected override void OnApplicationStarted() { base.OnApplicationStarted(); //routes and areas AreaRegistration.RegisterAllAreas(); RegisterRoutes(RouteTable.Routes); //Initializes a singleton that must reference this HttpApplication class, //in order to provide the Ninject Kernel to the rest of Thing.Web. This //is necessary because there are a few instances (currently Membership) //that require manual dependency injection. NinjectKernel.Instance = new NinjectKernel(this); //view model factory. NinjectKernel.Instance.Kernel.Bind<IModelFactory>().To<MasterModelFactory>(); } protected override NinjectControllerFactory CreateControllerFactory() { return base.CreateControllerFactory(); } protected override Ninject.IKernel CreateKernel() { var kernel = new StandardKernel(); kernel.Load("Thing.Web.Configuration.dll"); return kernel; } Now, everything works great, with one exception: For some reason, sometimes Ninject will bind the PhotoController twice. This leads to an ActivationException, because Ninject can't discern which PhotoController I want. This causes all requests for thumbnails and other user images on the site to fail. Here is the PhotoController in it's entirety: public class PhotoController : Controller { public PhotoController() { } public ActionResult Index(string id) { var dir = Server.MapPath("~/" + ConfigurationManager.AppSettings["UserPhotos"]); var path = Path.Combine(dir, id); return base.File(path, "image/jpeg"); } } Every controller works in exactly the same way, but for some reason the PhotoController gets double-bound. Even then, it only happens occasionally (either when re-building the solution, or on staging/production when the app pool kicks in). Once this happens, it continues to happen until I redeploy without changing anything. So...what's up with that?

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Can I write a test that succeeds if and only if a statement does not compile?

- by Billy ONeal

I'd like to prevent clients of my class from doing something stupid. To that end, I have used the type system, and made my class only accept specific types as input. Consider the following example (Not real code, I've left off things like virtual destructors for the sake of example): class MyDataChunk { //Look Ma! Implementation! }; class Sink; class Source { virtual void Run() = 0; Sink *next_; void SetNext(Sink *next) { next_ = next; } }; class Sink { virtual void GiveMeAChunk(const MyDataChunk& data) { //Impl }; }; class In { virtual void Run { //Impl } }; class Out { }; //Note how filter and sorter have the same declaration. Concrete classes //will inherit from them. The seperate names are there to ensure only //that some idiot doesn't go in and put in a filter where someone expects //a sorter, etc. class Filter : public Source, public Sink { //Drop objects from the chain-of-command pattern that don't match a particular //criterion. }; class Sorter : public Source, public Sink { //Sorts inputs to outputs. There are different sorters because someone might //want to sort by filename, size, date, etc... }; class MyClass { In i; Out o; Filter f; Sorter s; public: //Functions to set i, o, f, and s void Execute() { i.SetNext(f); f.SetNext(s); s.SetNext(o); i.Run(); } }; What I don't want is for somebody to come back later and go, "Hey, look! Sorter and Filter have the same signature. I can make a common one that does both!", thus breaking the semantic difference MyClass requires. Is this a common kind of requirement, and if so, how might I implement a test for it?

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SVG via dynamic XML+XSL

- by Daniel

This is a bit of a vague notion which I have been running over in my head, and which I am very curious if there is an elegant method of solving. Perhaps it should be taken as a thought experiment. Imagine you have an XML schema with a corresponding XSL transform, which renders the XML as SVG in the browser. The XSL generates SVG with appropriate Javascript handlers that, ultimately, implement editing-like functionality such that properties of the objects or their locations on the SVG canvas can be edited by the user. For instance, an element can be dragged from one location to another. Now, this isn't particularly difficult - the drag/drop example is simply a matter of changing the (x,y) coordinates of the SVG object, or a resize operation would be a simple matter of changing its width or height. But is there an elegant way to have Javascript work on the DOM of the source XML document instead of the rendered SVG? Why, you ask? Well, imagine you have very complex XSL transforms, where the modification of one property results in complex changes to the SVG. You want to maintain simplicity in your Javascript code, but also a simple way to persist the modified XML back to the server. Some possibilities of how this may function: After modification of the source DOM, simply re-run the XSL transform and replace the original. Downside: brute force, potentially expensive operation. Create id/class naming conventions in the source and target XML/SVG so elements can be related back to each other, and do an XSL transform on only a subset of the new DOM. In other words, modify temporary DOM, apply XSL to it, remove changed elements from SVG, and insert the new one. Downside: May not be possible to apply XSL to temporary in-browser DOMs(?). Also, perhaps a bit convoluted or ugly to maintain. I think that it may be possible to come up with a framework that handles the second scenario, but the challenge would be making it lightweight and not heavily tied to the actual XML schema. Any ideas or other possibilities? Or is there maybe an existing method of doing this which I'm not aware of? UPDATE: To clarify, as I mentioned in a comment below, this aids in separating the draw code from the edit code. For a more concrete example of how this is useful, imagine an element which determines how it is drawn dependent on the value of a property of an adjacent element. It's better to condense that logic directly in the draw code instead of also duplicating it in the edit code.

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data from few MySQL tables sorted by ASC

- by Andrew

In the dbase I 've few tables named as aaa_9xxx, aaa_9yyy, aaa_9zzz. I want to find all data with a specified DATE and show it with the TIME ASC. First, I must find a tables in the dbase: $STH_1a = $DBH->query("SELECT table_name FROM information_schema.tables WHERE table_name LIKE 'aaa\_9%' "); foreach($STH_1a as $row) { $table_name_s1[] = $row['table_name']; } Second, I must find a data wit a concrete date and show it with TIME ASC: foreach($table_name_s1 as $table_name_1) { $STH_1a2 = $DBH->query("SELECT * FROM `$table_name_1` WHERE date = '2011-11-11' ORDER BY time ASC "); while ($row = $STH_1a2->fetch(PDO::FETCH_ASSOC)) { echo " ".$table_name_1."-".$row['time']."-".$row['ei_name']." <br>"; } } .. but it shows the data sorted by tables name, then by TIME ASC. I must to have all this data (from all tables) sorted by TIME ASC. Thank You dev-null-dweller, Andrew Stubbs and Jaison Erick for your help. I test the Erick solution : foreach($STH_1a as $row) { $stmts[] = sprintf('SELECT * FROM %s WHERE date="%s"', $row['table_name'], '2011-11-11'); } $stmt = implode("\nUNION\n", $stmts); $stmt .= "\nORDER BY time ASC"; $STH_1a2 = $DBH->query($stmt); while ($row_1a2 = $STH_1a2->fetch(PDO::FETCH_ASSOC)) { echo " ".$row['table_name']."-".$row_1a2['time']."-".$row_1a2['ei_name']." <br>"; } it's working but I've problem with 'table_name' - it's always the LAST table name. //---------------------------------------------------------------------- end the ending solution with all fixes, thanks all for your help, :)) foreach($STH_1a as $row) { $stmts[] = sprintf("SELECT *, '%s' AS table_name FROM %s WHERE date='%s'", $row['table_name'], $row['table_name'], '2011-11- 11'); } $stmt = implode("\nUNION\n", $stmts); $stmt .= "\nORDER BY time ASC"; $STH_1a2 = $DBH->query($stmt); while ($row_1a2 = $STH_1a2->fetch(PDO::FETCH_ASSOC)) { echo " ".$row_1a2['table_name']."-".$row_1a2['time']."-".$row_1a2['ei_name']." <br>"; }

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Separation of domain and ui layer in a composite

- by hansmaad

Hi all, i'm wondering if there is a pattern how to separate the domain logic of a class from the ui responsibilities of the objects in the domain layer. Example: // Domain classes interface MachinePart { CalculateX(in, out) // Where do we put these: // Draw(Screen) ?? // ShowProperties(View) ?? // ... } class Assembly : MachinePart { CalculateX(in, out) subParts } class Pipe : MachinePart { CalculateX(in, out) length, diamater... } There is an application that calculates the value X for machines assembled from many machine parts. The assembly is loaded from a file representation and is designed as a composite. Each concrete part class stores some data to implement the CalculateX(in,out) method to simulate behaviour of the whole assembly. The application runs well but without GUI. To increase the usability a GUi should be developed on top of the existing implementation (changes to the existing code are allowed). The GUI should show a schematic graphical representation of the assembly and provide part specific dialogs to edit several parameters. To achieve these goals the application needs new functionality for each machine part to draw a schematic representation on the screen, show a property dialog and other things not related to the domain of machine simulation. I can think of some different solutions to implement a Draw(Screen) functionality for each part but i am not happy with each of them. First i could add a Draw(Screen) method to the MachinePart interface but this would mix-up domain code with ui code and i had to add a lot of functionality to each machine part class what makes my domain model hard to read and hard to understand. Another "simple" solution is to make all parts visitable and implement ui code in visitors but Visitor does not belong to my favorite patterns. I could derive UI variants from each machine part class to add the UI implementation there but i had to check if each part class is suited for inheritance and had to be careful on changes to the base classes. My currently favorite design is to create a parallel composite hierarchy where each component stores data to define a machine part, has implementation for UI methods and a factory method which creates instances of the corresponding domain classes, so that i can "convert" a UI assembly to a domain assembly. But there are problems to go back from the created domain hierarchy to the UI hierarchy for showing calculation results in the drawing for example (imagine some parts store some values during the calculation i want to show in the schematic representation after the simluation). Maybe there are some proven patterns for such problems?

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How to approach copying objects with smart pointers as class attributes?

- by tomislav-maric

From the boost library documentation I read this: Conceptually, smart pointers are seen as owning the object pointed to, and thus responsible for deletion of the object when it is no longer needed. I have a very simple problem: I want to use RAII for pointer attributes of a class that is Copyable and Assignable. The copy and assignment operations should be deep: every object should have its own copy of the actual data. Also, RTTI needs to be available for the attributes (their type may also be determined at runtime). Should I be searching for an implementation of a Copyable smart pointer (the data are small, so I don't need Copy on Write pointers), or do I delegate the copy operation to the copy constructors of my objects as shown in this answer? Which smart pointer do I choose for simple RAII of a class that is copyable and assignable? (I'm thinking that the unique_ptr with delegated copy/assignment operations to the class copy constructor and assignment operator would make a proper choice, but I am not sure) Here's a pseudocode for the problem using raw pointers, it's just a problem description, not a running C++ code: // Operation interface class ModelOperation { public: virtual void operate = (); }; // Implementation of an operation called Special class SpecialModelOperation : public ModelOperation { private: // Private attributes are present here in a real implementation. public: // Implement operation void operate () {}; }; // All operations conform to ModelOperation interface // These are possible operation names: // class MoreSpecialOperation; // class DifferentOperation; // Concrete model with different operations class MyModel { private: ModelOperation* firstOperation_; ModelOperation* secondOperation_; public: MyModel() : firstOperation_(0), secondOperation_(0) { // Forgetting about run-time type definition from input files here. firstOperation_ = new MoreSpecialOperation(); secondOperation_ = new DifferentOperation(); } void operate() { firstOperation_->operate(); secondOperation_->operate(); } ~MyModel() { delete firstOperation_; firstOperation_ = 0; delete secondOperation_; secondOperation_ = 0; } }; int main() { MyModel modelOne; // Some internal scope { // I want modelTwo to have its own set of copied, not referenced // operations, and at the same time I need RAII to work for it, // as soon as it goes out of scope. MyModel modelTwo (modelOne); } return 0; }

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C++ abstract class template + type-specific subclass = trouble with linker

- by user333279

Hi there, The project in question is about different endpoints communicating with each other. An endpoint sends events (beyond the scope of the current problem) and can process incoming events. Each event is represented in a generic object as follows: #pragma interface ... // some includes template<typename T> class Event { public: Event(int senderId, Type type, T payload); // Type is an enum Event(int senderId, Type type, int priority, T payload); virtual ~Event(); virtual int getSenderId(); virtual int getPriority(); virtual T getPayload(); void setPriority(const int priority); protected: const int senderId; const Type type; const T payload; int priority; }; It has its implementing class with #pragma implementation tag. An endpoint is defined as follows: #pragma interface #include "Event.h" template<typename T> class AbstractEndPoint { public: AbstractEndPoint(int id); virtual ~AbstractEndPoint(); virtual int getId(); virtual void processEvent(Event<T> event) = 0; protected: const int id; }; It has its implementing class too, but only the constructor, destructor and getId() are defined. The idea is to create concrete endpoints for each different payload type. Therefore I have different payload objects and specific event classes for each type, e.g. Event<TelegramFormatA>, Event<TelegramFormatB> and ConcreteEndPoint for TelegramFormatA, ConcreteEndPoint for TelegramFormatB respectively. The latter classes are defined as class ConcreteEndPoint : AbstractEndPoint<TelegramFormatA> { ... } I'm using g++ 4.4.3 and ld 2.19. Everything compiles nicely, but the linker complaints about undefined references to type-specific event classes, like Event<TelegramFormatA>::Event(....) . I tried explicit instantiation using template class AbstractEndPoint<TelegramFormatA>; but couldn't get past the aforementioned linker errors. Any ideas would be appreciated.

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Is it a good or bad practice to call instance methods from a java constructor?

- by Steve

There are several different ways I can initialize complex objects (with injected dependencies and required set-up of injected members), are all seem reasonable, but have various advantages and disadvantages. I'll give a concrete example: final class MyClass { private final Dependency dependency; @Inject public MyClass(Dependency dependency) { this.dependency = dependency; dependency.addHandler(new Handler() { @Override void handle(int foo) { MyClass.this.doSomething(foo); } }); doSomething(0); } private void doSomething(int foo) { dependency.doSomethingElse(foo+1); } } As you can see, the constructor does 3 things, including calling an instance method. I've been told that calling instance methods from a constructor is unsafe because it circumvents the compiler's checks for uninitialized members. I.e. I could have called doSomething(0) before setting this.dependency, which would have compiled but not worked. What is the best way to refactor this? Make doSomething static and pass in the dependency explicitly? In my actual case I have three instance methods and three member fields that all depend on one another, so this seems like a lot of extra boilerplate to make all three of these static. Move the addHandler and doSomething into an @Inject public void init() method. While use with Guice will be transparent, it requires any manual construction to be sure to call init() or else the object won't be fully-functional if someone forgets. Also, this exposes more of the API, both of which seem like bad ideas. Wrap a nested class to keep the dependency to make sure it behaves properly without exposing additional API:class DependencyManager { private final Dependency dependency; public DependecyManager(Dependency dependency) { ... } public doSomething(int foo) { ... } } @Inject public MyClass(Dependency dependency) { DependencyManager manager = new DependencyManager(dependency); manager.doSomething(0); } This pulls instance methods out of all constructors, but generates an extra layer of classes, and when I already had inner and anonymous classes (e.g. that handler) it can become confusing - when I tried this I was told to move the DependencyManager to a separate file, which is also distasteful because it's now multiple files to do a single thing. So what is the preferred way to deal with this sort of situation?

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Why is my Type.GetFields(BindingFlags.Instance|BindingFlags.Public) not working?

- by granadaCoder

My code can see the non-public members, but not the public ones. Why? FieldInfo[] publicFieldInfos = t.GetFields(BindingFlags.Instance | BindingFlags.Public); is returning nothing. Note: I'm trying to get at the properties on the abstract class as well as the concrete class. (And read the attributes as well). The MSDN example works with the 2 flags (BindingFlags.Instance | BindingFlags.Public) but my mini inheritance example below does not. private void RunTest1() { try { textBox1.Text = string.Empty; Type t = typeof(MyInheritedClass); //Look at the BindingFlags *** NonPublic *** int fieldCount = 0; while (null != t) { fieldCount += t.GetFields(BindingFlags.Instance | BindingFlags.NonPublic).Length; FieldInfo[] nonPublicFieldInfos = t.GetFields(BindingFlags.Instance | BindingFlags.NonPublic); foreach (FieldInfo field in nonPublicFieldInfos) { if (null != field) { Console.WriteLine(field.Name); } } t = t.BaseType; } Console.WriteLine("\n\r------------------\n\r"); //Look at the BindingFlags *** Public *** t = typeof(MyInheritedClass); FieldInfo[] publicFieldInfos = t.GetFields(BindingFlags.Instance | BindingFlags.Public); foreach (FieldInfo field in publicFieldInfos) { if (null != field) { Console.WriteLine(field.Name); object[] attributes = field.GetCustomAttributes(t, true); if (attributes != null && attributes.Length > 0) { foreach (Attribute att in attributes) { Console.WriteLine(att.GetType().Name); } } } } } catch (Exception ex) { ReportException(ex); } } private void ReportException(Exception ex) { Exception innerException = ex; while (innerException != null) { Console.WriteLine(innerException.Message + System.Environment.NewLine + innerException.StackTrace + System.Environment.NewLine + System.Environment.NewLine); innerException = innerException.InnerException; } } public abstract class MySuperType { public MySuperType(string st) { this.STString = st; } public string STString { get; set; } public abstract string MyAbstractString { get; set; } } public class MyInheritedClass : MySuperType { public MyInheritedClass(string ic) : base(ic) { this.ICString = ic; } [Description("This is an important property"), Category("HowImportant")] public string ICString { get; set; } private string _oldSchoolPropertyString = string.Empty; public string OldSchoolPropertyString { get { return _oldSchoolPropertyString; } set { _oldSchoolPropertyString = value; } } [Description("This is a not so importarnt property"), Category("HowImportant")] public override string MyAbstractString { get; set; } }

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CakePHP 3-level-deep model associatons

- by user357452

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Why is my (Type).GetFields(BindingFlags.Instance | BindingFlags.Public) not working?

- by granadaCoder

My code can see the NonPublic members, but not the Public ones. (???) Full sample code below. FieldInfo[] publicFieldInfos = t.GetFields(BindingFlags.Instance | BindingFlags.Public); is returning nothing. Note, I'm trying to get at the properties on the abstract class as well as the 1 concrete class. (And read the attributes as well). I'm going bonkers on this one....the msdn example works with the 2 flags (BindingFlags.Instance | BindingFlags.Public).....but my mini inheritance example below is not. THANKS in advance. /////////////START CODE private void RunTest1() { try { textBox1.Text = string.Empty; Type t = typeof(MyInheritedClass); //Look at the BindingFlags *** NonPublic *** int fieldCount = 0; while (null != t) { fieldCount += t.GetFields(BindingFlags.Instance | BindingFlags.NonPublic).Length; FieldInfo[] nonPublicFieldInfos = t.GetFields(BindingFlags.Instance | BindingFlags.NonPublic); foreach (FieldInfo field in nonPublicFieldInfos) { if (null != field) { Console.WriteLine(field.Name); } } t = t.BaseType; } Console.WriteLine("\n\r------------------\n\r"); //Look at the BindingFlags *** Public *** t = typeof(MyInheritedClass); FieldInfo[] publicFieldInfos = t.GetFields(BindingFlags.Instance | BindingFlags.Public); foreach (FieldInfo field in publicFieldInfos) { if (null != field) { Console.WriteLine(field.Name); object[] attributes = field.GetCustomAttributes(t, true); if (attributes != null && attributes.Length > 0) { foreach (Attribute att in attributes) { Console.WriteLine(att.GetType().Name); } } } } } catch (Exception ex) { ReportException(ex); } } private void ReportException(Exception ex) { Exception innerException = ex; while (innerException != null) { Console.WriteLine(innerException.Message + System.Environment.NewLine + innerException.StackTrace + System.Environment.NewLine + System.Environment.NewLine); innerException = innerException.InnerException; } } public abstract class MySuperType { public MySuperType(string st) { this.STString = st; } public string STString { get; set; } public abstract string MyAbstractString {get;set;} } public class MyInheritedClass : MySuperType { public MyInheritedClass(string ic) : base(ic) { this.ICString = ic; } [Description("This is an important property"),Category("HowImportant")] public string ICString { get; set; } private string _oldSchoolPropertyString = string.Empty; public string OldSchoolPropertyString { get { return _oldSchoolPropertyString; } set { _oldSchoolPropertyString = value; } } [Description("This is a not so importarnt property"), Category("HowImportant")] public override string MyAbstractString { get; set; } }

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Users and roles in context

- by Eric W.

I'm trying to get a sense of how to implement the user/role relationships for an application I'm writing. The persistence layer is Google App Engine's datastore, which places some interesting (but generally beneficial) constraints on what can be done. Any thoughts are appreciated. It might be helpful to keep things very concrete. I would like there to be organizations, users, test content and test administrations (records of tests that have been taken). A user can have the role of participant (test-taker), contributor of test material or both. A user can also be a member of zero or more organizations. In the role of participant, the user can see the previous administrations of tests he or she has taken. The user can also see a test administration of another participant if that participant has given the user authorization. The user can see test material that has been made public, and he or she can see restricted content as a participant during a specific administration of a test for which that user has been authorized by an organization. As a member of an organization, the user can see restricted content in the role of contributor, and he or she might or might not also be able to edit the content. Each organization should have one or more administrators that can determine whether a member can see and edit content and determine who has admin privileges. There should also be one or more application-wide superusers that can troubleshoot and solve problems. Members of organizations can see the administrations of tests that the participants concerned have authorized them to see, and they can see anonymous data if no authorization has been given. A user cannot see the test results of another user in any other circumstances. Since there are no joins in the App Engine datastore, it might be necessary to have things less normalized than usual for the typical SQL database in order to ensure that queries that check permissions are fast (e.g., ones that determine whether a link is to be displayed). My questions are: How do I move forward on this? Should I spend a lot of time up front in order to get the model right, or can I iterate several times and gradually roll in additional complexity? Does anyone have some general ideas about how to break things up in this instance? Are there any GAE libraries that handle roles in a way that is compatible with this arrangement?

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MS Ajax Libraries and Configured Assemblies

- by smehaffie

Use Case You have a brand new IIS servers that has .Net 3.5 installed and are migrating sites to the new servers. In the process of migrating sites you come across some sites that get an error about the version of AJAX libraries being references in the web.config. In the web.config all the entries reference 1.0.61025.0, but the older version of the AJAX libraries are not installed on the new servers, only the latest version is installed that comes with .Net 3.5. So what are the options to fix this issue. Solutions 1) Install the older version of the AJAX Libraries: Although this works, IMO it is never a great idea to install an older version of a library after a newer version has been installed. Plus, if all new application use the latest versions, is it worth the effort of installing the older version for a few legacy applications? 2) Update the web.config files so all references use latest version (3.5.0.0): This option is very time consuming and error prone. In addition, you will also have to update any pages where there is a register tag for the older libraries as well. This would require you to redeploy any application that have this issue. 3) Use the Configured Assembly capabilities of .Net (aka: Assembly Bindings) to make any application that uses the older AJAX libraries to use the new AJAX libraries. IMO, this is the easiest, quickest and least invasive way to fix the issue. Below are the steps to implement this fix. Solution #3 Do the following steps on the IIS servers that the issue is occurring. The 2 assemblies that need assemblies bindings created are: System.Web.Extension & System.Web.Extensions.Design 1) Go to Start - > All Program -> Administrative Tools -> Microsoft .NET Framework 2.0 Configuration. 2) Right click on "Configured Assemblies" to view list of configured assemblies. 3) Left Click on right pane to bring up menu and choose "Add". 4) Make sure "Choose and assembly from the assembly cache is checked" and click the "Choose Assembly" button. 5) Choose System.Web.Extension (does not matter what version). 6) Click the "Finish" button. 7) Binding Policy Tab - Enter Requested Version = 1.0.61025.0 - Enter New Version = 3.5.0.0 8) Repeat steps 2-7 for the System.Web.Extensions.Design assembly. --------------------------------------------------------------------------------------------------------------------------------------------------------- Note: If "Microsoft .NET Framework 2.0 Configuration does not exist under Admin tools use mmc to access it (see below) 1) Start -> Run -> Enter MMC 2) File - > Add/Remove Snap-In then Click "Add" button 3) Choose ".Net 2.0 Configuration" then click "Add" button and then the "Close" Button. 4) On "Add/Remove Snapin" windows click the "OK" Button. 5) Expand the tree on the right and you can start following the directions above for adding the configured assemblies. ---------------------------------------------------------------------------------------------------------------------------------------------------------

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From Binary to Data Structures

- by Cédric Menzi

Table of Contents Introduction PE file format and COFF header COFF file header BaseCoffReader Byte4ByteCoffReader UnsafeCoffReader ManagedCoffReader Conclusion History This article is also available on CodeProject Introduction Sometimes, you want to parse well-formed binary data and bring it into your objects to do some dirty stuff with it. In the Windows world most data structures are stored in special binary format. Either we call a WinApi function or we want to read from special files like images, spool files, executables or may be the previously announced Outlook Personal Folders File. Most specifications for these files can be found on the MSDN Libarary: Open Specification In my example, we are going to get the COFF (Common Object File Format) file header from a PE (Portable Executable). The exact specification can be found here: PECOFF PE file format and COFF header Before we start we need to know how this file is formatted. The following figure shows an overview of the Microsoft PE executable format. Source: Microsoft Our goal is to get the PE header. As we can see, the image starts with a MS-DOS 2.0 header with is not important for us. From the documentation we can read "...After the MS DOS stub, at the file offset specified at offset 0x3c, is a 4-byte...". With this information we know our reader has to jump to location 0x3c and read the offset to the signature. The signature is always 4 bytes that ensures that the image is a PE file. The signature is: PE\0\0. To prove this we first seek to the offset 0x3c, read if the file consist the signature. So we need to declare some constants, because we do not want magic numbers. private const int PeSignatureOffsetLocation = 0x3c; private const int PeSignatureSize = 4; private const string PeSignatureContent = "PE"; Then a method for moving the reader to the correct location to read the offset of signature. With this method we always move the underlining Stream of the BinaryReader to the start location of the PE signature. private void SeekToPeSignature(BinaryReader br) { // seek to the offset for the PE signagure br.BaseStream.Seek(PeSignatureOffsetLocation, SeekOrigin.Begin); // read the offset int offsetToPeSig = br.ReadInt32(); // seek to the start of the PE signature br.BaseStream.Seek(offsetToPeSig, SeekOrigin.Begin); } Now, we can check if it is a valid PE image by reading of the next 4 byte contains the content PE. private bool IsValidPeSignature(BinaryReader br) { // read 4 bytes to get the PE signature byte[] peSigBytes = br.ReadBytes(PeSignatureSize); // convert it to a string and trim \0 at the end of the content string peContent = Encoding.Default.GetString(peSigBytes).TrimEnd('\0'); // check if PE is in the content return peContent.Equals(PeSignatureContent); } With this basic functionality we have a good base reader class to try the different methods of parsing the COFF file header. COFF file header The COFF header has the following structure: Offset Size Field 0 2 Machine 2 2 NumberOfSections 4 4 TimeDateStamp 8 4 PointerToSymbolTable 12 4 NumberOfSymbols 16 2 SizeOfOptionalHeader 18 2 Characteristics If we translate this table to code, we get something like this: [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)] public struct CoffHeader { public MachineType Machine; public ushort NumberOfSections; public uint TimeDateStamp; public uint PointerToSymbolTable; public uint NumberOfSymbols; public ushort SizeOfOptionalHeader; public Characteristic Characteristics; } BaseCoffReader All readers do the same thing, so we go to the patterns library in our head and see that Strategy pattern or Template method pattern is sticked out in the bookshelf. I have decided to take the template method pattern in this case, because the Parse() should handle the IO for all implementations and the concrete parsing should done in its derived classes. public CoffHeader Parse() { using (var br = new BinaryReader(File.Open(_fileName, FileMode.Open, FileAccess.Read, FileShare.Read))) { SeekToPeSignature(br); if (!IsValidPeSignature(br)) { throw new BadImageFormatException(); } return ParseInternal(br); } } protected abstract CoffHeader ParseInternal(BinaryReader br); First we open the BinaryReader, seek to the PE signature then we check if it contains a valid PE signature and rest is done by the derived implementations. Byte4ByteCoffReader The first solution is using the BinaryReader. It is the general way to get the data. We only need to know which order, which data-type and its size. If we read byte for byte we could comment out the first line in the CoffHeader structure, because we have control about the order of the member assignment. protected override CoffHeader ParseInternal(BinaryReader br) { CoffHeader coff = new CoffHeader(); coff.Machine = (MachineType)br.ReadInt16(); coff.NumberOfSections = (ushort)br.ReadInt16(); coff.TimeDateStamp = br.ReadUInt32(); coff.PointerToSymbolTable = br.ReadUInt32(); coff.NumberOfSymbols = br.ReadUInt32(); coff.SizeOfOptionalHeader = (ushort)br.ReadInt16(); coff.Characteristics = (Characteristic)br.ReadInt16(); return coff; } If the structure is as short as the COFF header here and the specification will never changed, there is probably no reason to change the strategy. But if a data-type will be changed, a new member will be added or ordering of member will be changed the maintenance costs of this method are very high. UnsafeCoffReader Another way to bring the data into this structure is using a "magically" unsafe trick. As above, we know the layout and order of the data structure. Now, we need the StructLayout attribute, because we have to ensure that the .NET Runtime allocates the structure in the same order as it is specified in the source code. We also need to enable "Allow unsafe code (/unsafe)" in the project's build properties. Then we need to add the following constructor to the CoffHeader structure. [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)] public struct CoffHeader { public CoffHeader(byte[] data) { unsafe { fixed (byte* packet = &data[0]) { this = *(CoffHeader*)packet; } } } } The "magic" trick is in the statement: this = *(CoffHeader*)packet;. What happens here? We have a fixed size of data somewhere in the memory and because a struct in C# is a value-type, the assignment operator = copies the whole data of the structure and not only the reference. To fill the structure with data, we need to pass the data as bytes into the CoffHeader structure. This can be achieved by reading the exact size of the structure from the PE file. protected override CoffHeader ParseInternal(BinaryReader br) { return new CoffHeader(br.ReadBytes(Marshal.SizeOf(typeof(CoffHeader)))); } This solution is the fastest way to parse the data and bring it into the structure, but it is unsafe and it could introduce some security and stability risks. ManagedCoffReader In this solution we are using the same approach of the structure assignment as above. But we need to replace the unsafe part in the constructor with the following managed part: [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)] public struct CoffHeader { public CoffHeader(byte[] data) { IntPtr coffPtr = IntPtr.Zero; try { int size = Marshal.SizeOf(typeof(CoffHeader)); coffPtr = Marshal.AllocHGlobal(size); Marshal.Copy(data, 0, coffPtr, size); this = (CoffHeader)Marshal.PtrToStructure(coffPtr, typeof(CoffHeader)); } finally { Marshal.FreeHGlobal(coffPtr); } } } Conclusion We saw that we can parse well-formed binary data to our data structures using different approaches. The first is probably the clearest way, because we know each member and its size and ordering and we have control about the reading the data for each member. But if add member or the structure is going change by some reason, we need to change the reader. The two other solutions use the approach of the structure assignment. In the unsafe implementation we need to compile the project with the /unsafe option. We increase the performance, but we get some security risks.

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