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  • Isn't MVC anti OOP?

    - by m3th0dman
    The main idea behind OOP is to unify data and behavior in a single entity - the object. In procedural programming there is data and separately algorithms modifying the data. In the Model-View-Controller pattern the data and the logic/algorithms are placed in distinct entities, the model and the controller respectively. In an equivalent OOP approach shouldn't the model and the controller be placed in the same logical entity?

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  • Super constructor must be a first statement in Java constructor [closed]

    - by Val
    I know the answer: "we need rules to prevent shooting into your own foot". Ok, I make millions of programming mistakes every day. To be prevented, we need one simple rule: prohibit all JLS and do not use Java. If we explain everything by "not shooting your foot", this is reasonable. But there is not much reason is such reason. When I programmed in Delphy, I always wanted the compiler to check me if I read uninitializable. I have discovered myself that is is stupid to read uncertain variable because it leads unpredictable result and is errorenous obviously. By just looking at the code I could see if there is an error. I wished if compiler could do this job. It is also a reliable signal of programming error if function does not return any value. But I never wanted it do enforce me the super constructor first. Why? You say that constructors just initialize fields. Super fields are derived; extra fields are introduced. From the goal point of view, it does not matter in which order you initialize the variables. I have studied parallel architectures and can say that all the fields can even be assigned in parallel... What? Do you want to use the unitialized fields? Stupid people always want to take away our freedoms and break the JLS rules the God gives to us! Please, policeman, take away that person! Where do I say so? I'm just saying only about initializing/assigning, not using the fields. Java compiler already defends me from the mistake of accessing notinitialized. Some cases sneak but this example shows how this stupid rule does not save us from the read-accessing incompletely initialized in construction: public class BadSuper { String field; public String toString() { return "field = " + field; } public BadSuper(String val) { field = val; // yea, superfirst does not protect from accessing // inconstructed subclass fields. Subclass constr // must be called before super()! System.err.println(this); } } public class BadPost extends BadSuper { Object o; public BadPost(Object o) { super("str"); this. o = o; } public String toString() { // superconstructor will boom here, because o is not initialized! return super.toString() + ", obj = " + o.toString(); } public static void main(String[] args) { new BadSuper("test 1"); new BadPost(new Object()); } } It shows that actually, subfields have to be inilialized before the supreclass! Meantime, java requirement "saves" us from writing specializing the class by specializing what the super constructor argument is, public class MyKryo extends Kryo { class MyClassResolver extends DefaultClassResolver { public Registration register(Registration registration) { System.out.println(MyKryo.this.getDepth()); return super.register(registration); } } MyKryo() { // cannot instantiate MyClassResolver in super super(new MyClassResolver(), new MapReferenceResolver()); } } Try to make it compilable. It is always pain. Especially, when you cannot assign the argument later. Initialization order is not important for initialization in general. I could understand that you should not use super methods before initializing super. But, the requirement for super to be the first statement is different. It only saves you from the code that does useful things simply. I do not see how this adds safety. Actually, safety is degraded because we need to use ugly workarounds. Doing post-initialization, outside the constructors also degrades safety (otherwise, why do we need constructors?) and defeats the java final safety reenforcer. To conclude Reading not initialized is a bug. Initialization order is not important from the computer science point of view. Doing initalization or computations in different order is not a bug. Reenforcing read-access to not initialized is good but compilers fail to detect all such bugs Making super the first does not solve the problem as it "Prevents" shooting into right things but not into the foot It requires to invent workarounds, where, because of complexity of analysis, it is easier to shoot into the foot doing post-initialization outside the constructors degrades safety (otherwise, why do we need constructors?) and that degrade safety by defeating final access modifier When there was java forum alive, java bigots attecked me for these thoughts. Particularly, they dislaked that fields can be initialized in parallel, saying that natural development ensures correctness. When I replied that you could use an advanced engineering to create a human right away, without "developing" any ape first, and it still be an ape, they stopped to listen me. Cos modern technology cannot afford it. Ok, Take something simpler. How do you produce a Renault? Should you construct an Automobile first? No, you start by producing a Renault and, once completed, you'll see that this is an automobile. So, the requirement to produce fields in "natural order" is unnatural. In case of alarmclock or armchair, which are still chair and clock, you may need first develop the base (clock and chair) and then add extra. So, I can have examples where superfields must be initialized first and, oppositely, when they need to be initialized later. The order does not exist in advance. So, the compiler cannot be aware of the proper order. Only programmer/constructor knows is. Compiler should not take more responsibility and enforce the wrong order onto programmer. Saying that I cannot initialize some fields because I did not ininialized the others is like "you cannot initialize the thing because it is not initialized". This is a kind of argument we have. So, to conclude once more, the feature that "protects" me from doing things in simple and right way in order to enforce something that does not add noticeably to the bug elimination at that is a strongly negative thing and it pisses me off, altogether with the all the arguments to support it I've seen so far. It is "a conceptual question about software development" Should there be the requirement to call super() first or not. I do not know. If you do or have an idea, you have place to answer. I think that I have provided enough arguments against this feature. Lets appreciate the ones who benefit form it. Let it just be something more than simple abstract and stupid "write your own language" or "protection" kind of argument. Why do we need it in the language that I am going to develop?

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  • Making a design for a Problem [closed]

    - by Vaibhav Agarwal
    I have written many codes using OOPS and I am still to understand when is a code good enough to be accepted by experts. The thought procedure of every man is different and so is the design. My question is should I do something in particular to design my programs in such a way that they are good enough to be accepted by people. Other thing I have also read Head First Object Oriented Design but at last I feel that the way they design the problems is much different I would have designed them.

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  • Are UML class diagrams adequated to design javascript systems?

    - by Vandell
    Given that UML is oriented towards a more classic approach to object orientation, is it still usable in a reliable way to design javascript systems? One specific problem that I can see is that class diagrams are, in fact, a structural view of the system, and javascript is more behaviour driven, how can you deal with it? Please, keep in mind that I'm not talking abot the real world domain here, It's a model for the solution that I'm trying to achieve.

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  • What if globals make sense?

    - by Greg
    I've got a value that many objects need. For example, a financial application with different investments as objects, and most of them need the current interest rate. I was hoping to encapsulate my "financial environment" as an object, with the interest rate as a property. But, sibling objects that need that value can't get to it. So how do I share values among many objects without over-coupling my design? Obviously I'm thinking about this wrong.

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  • What is the difference between "data hiding" and "encapsulation"?

    - by Software Engeneering Learner
    I'm reading "Java concurrency in practice" and there is said: "Fortunately, the same object-oriented techniques that help you write well-organized, maintainable classes - such as encapsulation and data hiding -can also help you create thread-safe classes." The problem #1 - I never heard about data hiding and don't know what it is. The problem #2 - I always thought that encapsulation is using private vs public, and is actually the data hiding. Can you please explain what data hiding is and how it differs from encapsulation?

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  • Are UML class diagrams adequate to design javascript systems?

    - by Vandell
    Given that UML is oriented towards a more classic approach to object orientation, is it still usable in a reliable way to design javascript systems? One specific problem that I can see is that class diagrams are, in fact, a structural view of the system, and javascript is more behaviour driven, how can you deal with it? Please, keep in mind that I'm not talking abot the real world domain here, It's a model for the solution that I'm trying to achieve.

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  • How to store multiple requirements with OR and AND?

    - by Cano
    Well I'm working on a personal project that needs to check if a user has met certain requirements, and they come in a form of Requirement: [c1 OR c2] AND [d1 OR d2] Requirement: [c1 AND c2] OR [d1 AND d2] Requirement: c1 AND any dn(n can be any integer) I'm just not sure how to store these sorts of requirements, I'm thinking of using another object to hold c1,c2,d1,d2....dn and OR, but that seems like a roundabout way of doing things. Is there a better method?

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  • Upgrading SSIS Custom Components for SQL Server 2012

    Having finally got around to upgrading my custom components to SQL Server 2012, I thought I’d share some notes on the process. One of the goals was minimal duplication, so the same code files are used to build the 2008 and 2012 components, I just have a separate project file. The high level steps are listed below, followed by some more details. Create a 2012 copy of the project file Upgrade project, just open the new project file is VS2010 Change target framework to .NET 4.0 Set conditional compilation symbol for DENALI Change any conditional code, including assembly version and UI type name Edit project file to change referenced assemblies for 2012 Change target framework to .NET 4.0 Open the project properties. On the Applications page, change the Target framework to .NET Framework 4. Set conditional compilation symbol for DENALI Re-open the project properties. On the Build tab, first change the Configuration to All Configurations, then set a Conditional compilation symbol of DENALI. Change any conditional code, including assembly version and UI type name The value doesn’t have to be DENALI, it can actually be anything you like, that is just what I use. It is how I control sections of code that vary between versions. There were several API changes between 2005 and 2008, as well as interface name changes. Whilst we don’t have the same issues between 2008 and 2012, I still have some sections of code that do change such as the assembly attributes. #if DENALI [assembly: AssemblyDescription("Data Generator Source for SQL Server Integration Services 2012")] [assembly: AssemblyCopyright("Copyright © 2012 Konesans Ltd")] [assembly: AssemblyVersion("3.0.0.0")] #else [assembly: AssemblyDescription("Data Generator Source for SQL Server Integration Services 2008")] [assembly: AssemblyCopyright("Copyright © 2008 Konesans Ltd")] [assembly: AssemblyVersion("2.0.0.0")] #endif The Visual Studio editor automatically formats the code based on the current compilation symbols, hence in this case the 2008 code is grey to indicate it is disabled. As you can see in the previous example I have distinct assembly version attributes, ensuring I can run both 2008 and 2012 versions of my component side by side. For custom components with a user interface, be sure to update the UITypeName property of the DtsTask or DtsPipelineComponent attributes. As above I use the conditional compilation symbol to control the code. #if DENALI [DtsTask ( DisplayName = "File Watcher Task", Description = "File Watcher Task", IconResource = "Konesans.Dts.Tasks.FileWatcherTask.FileWatcherTask.ico", UITypeName = "Konesans.Dts.Tasks.FileWatcherTask.FileWatcherTaskUI,Konesans.Dts.Tasks.FileWatcherTask,Version=3.0.0.0,Culture=Neutral,PublicKeyToken=b2ab4a111192992b", TaskContact = "File Watcher Task; Konesans Ltd; Copyright © 2012 Konesans Ltd; http://www.konesans.com" )] #else [DtsTask ( DisplayName = "File Watcher Task", Description = "File Watcher Task", IconResource = "Konesans.Dts.Tasks.FileWatcherTask.FileWatcherTask.ico", UITypeName = "Konesans.Dts.Tasks.FileWatcherTask.FileWatcherTaskUI,Konesans.Dts.Tasks.FileWatcherTask,Version=2.0.0.0,Culture=Neutral,PublicKeyToken=b2ab4a111192992b", TaskContact = "File Watcher Task; Konesans Ltd; Copyright © 2004-2008 Konesans Ltd; http://www.konesans.com" )] #endif public sealed class FileWatcherTask: Task, IDTSComponentPersist, IDTSBreakpointSite, IDTSSuspend { // .. code goes on... } Shown below is another example I found that needed changing. I borrow one of the MS editors, and use it against a custom property, but need to ensure I reference the correct version of the MS controls assembly. This section of code is actually shared between the 2005, 2008 and 2012 versions of my component hence it has test for both DENALI and KATMAI symbols. #if DENALI const string multiLineUI = "Microsoft.DataTransformationServices.Controls.ModalMultilineStringEditor, Microsoft.DataTransformationServices.Controls, Version=11.0.00.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91"; #elif KATMAI const string multiLineUI = "Microsoft.DataTransformationServices.Controls.ModalMultilineStringEditor, Microsoft.DataTransformationServices.Controls, Version=10.0.0.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91"; #else const string multiLineUI = "Microsoft.DataTransformationServices.Controls.ModalMultilineStringEditor, Microsoft.DataTransformationServices.Controls, Version=9.0.242.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91"; #endif // Create Match Expression parameter IDTSCustomPropertyCollection100 propertyCollection = outputColumn.CustomPropertyCollection; IDTSCustomProperty100 property = propertyCollection.New(); property = propertyCollection.New(); property.Name = MatchParams.Name; property.Description = MatchParams.Description; property.TypeConverter = typeof(MultilineStringConverter).AssemblyQualifiedName; property.UITypeEditor = multiLineUI; property.Value = MatchParams.DefaultValue; Edit project file to change referenced assemblies for 2012 We now need to edit the project file itself. Open the MyComponente2012.cproj  in you favourite text editor, and then perform a couple of find and replaces as listed below: Find Replace Comment Version=10.0.0.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91 Version=11.0.0.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91 Change the assembly references version from SQL Server 2008 to SQL Server 2012. Microsoft SQL Server\100\ Microsoft SQL Server\110\ Change any assembly reference hint path locations from from SQL Server 2008 to SQL Server 2012. If you use any Build Events during development, such as copying the component assembly to the DTS folder, or calling GACUTIL to install it into the GAC, you can also change these now. An example of my new post-build event for a pipeline component is shown below, which uses the .NET 4.0 path for GACUTIL. It also uses the 110 folder location, instead of 100 for SQL Server 2008, but that was covered the the previous find and replace. "C:\Program Files (x86)\Microsoft SDKs\Windows\v7.0A\Bin\NETFX 4.0 Tools\gacutil.exe" /if "$(TargetPath)" copy "$(TargetPath)" "%ProgramFiles%\Microsoft SQL Server\110\DTS\PipelineComponents" /Y

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  • Handling null values and missing object properties in Silverlight 4

    - by PeterTweed
    Before Silverlight 4 to bind a data object to the UI and display a message associated with either a null value or if the binding path was wrong, you would need to write a Converter.  In Silverlight 4 we find the addition of the markup extensions TargetNullValue and FallbackValue that allows us to display a value when a null value is found in the bound to property and display a value when the property being bound to is not found. This post will show you how to use both markup extensions. Steps: 1. Create a new Silverlight 4 application 2. In the body of the MainPage.xaml.cs file replace the MainPage class with the following code:     public partial class MainPage : UserControl     {         public MainPage()         {             InitializeComponent();             this.Loaded += new RoutedEventHandler(MainPage_Loaded);         }           void MainPage_Loaded(object sender, RoutedEventArgs e)         {             person p = new person() { NameValue = "Peter Tweed" };             this.DataContext = p;         }     }       public class person     {         public string NameValue { get; set; }         public string TitleValue { get; set; }     } This code defines a class called person with two properties.  A new instance of the class is created, only defining the value for one of the properties and bound to the DataContext of the page. 3.  In the MainPage.xaml file copy the following XAML into the LayoutRoot grid:         <Grid.RowDefinitions>             <RowDefinition Height="60*" />             <RowDefinition Height="28*" />             <RowDefinition Height="28*" />             <RowDefinition Height="30*" />             <RowDefinition Height="154*" />         </Grid.RowDefinitions>         <Grid.ColumnDefinitions>             <ColumnDefinition Width="86*" />             <ColumnDefinition Width="314*" />         </Grid.ColumnDefinitions>         <TextBlock Grid.Row="1" Height="23" HorizontalAlignment="Left" Margin="32,0,0,0" Name="textBlock1" Text="Name Value:" VerticalAlignment="Top" />         <TextBlock Grid.Row="2" Height="23" HorizontalAlignment="Left" Margin="32,0,0,0" Name="textBlock2" Text="Title Value:" VerticalAlignment="Top" />         <TextBlock Grid.Row="3" Height="23" HorizontalAlignment="Left" Margin="32,0,0,0" Name="textBlock3" Text="Non Existant Value:" VerticalAlignment="Top" />         <TextBlock Grid.Column="1" Grid.Row="1" Height="23" HorizontalAlignment="Left" Name="textBlock4" Text="{Binding NameValue, TargetNullValue='No Name!!!!!!!'}" VerticalAlignment="Top" Margin="6,0,0,0" />         <TextBlock Grid.Column="1" Grid.Row="2" Height="23" HorizontalAlignment="Left" Name="textBlock5" Text="{Binding TitleValue, TargetNullValue='No Title!!!!!!!'}" VerticalAlignment="Top" Margin="6,0,0,0" />         <TextBlock Grid.Column="1" Grid.Row="3" Height="23" HorizontalAlignment="Left" Margin="6,0,0,0" Name="textBlock6" Text="{Binding AgeValue, FallbackValue='No such property!'}" VerticalAlignment="Top" />    This XAML defines three textblocks – two of which use the TargetNull and one that uses the FallbackValue markup extensions.  4. Run the application and see the person name displayed as defined for the person object, the expected string displayed for the TargetNullValue when no value exists for the boudn property and the expected string displayed for the FallbackValue when the property bound to is not found on the bound object. It's that easy!

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  • OpenGL Fast-Object Instancing Error

    - by HJ Media Studios
    I have some code that loops through a set of objects and renders instances of those objects. The list of objects that needs to be rendered is stored as a std::map, where an object of class MeshResource contains the vertices and indices with the actual data, and an object of classMeshRenderer defines the point in space the mesh is to be rendered at. My rendering code is as follows: glDisable(GL_BLEND); glEnable(GL_CULL_FACE); glDepthMask(GL_TRUE); glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glEnable(GL_DEPTH_TEST); for (std::map<MeshResource*, std::vector<MeshRenderer*> >::iterator it = renderables.begin(); it != renderables.end(); it++) { it->first->setupBeforeRendering(); cout << "<"; for (unsigned long i =0; i < it->second.size(); i++) { //Pass in an identity matrix to the vertex shader- used here only for debugging purposes; the real code correctly inputs any matrix. uniformizeModelMatrix(Matrix4::IDENTITY); /** * StartHere fix rendering problem. * Ruled out: * Vertex buffers correctly. * Index buffers correctly. * Matrices correct? */ it->first->render(); } it->first->cleanupAfterRendering(); } geometryPassShader->disable(); glDepthMask(GL_FALSE); glDisable(GL_CULL_FACE); glDisable(GL_DEPTH_TEST); The function in MeshResource that handles setting up the uniforms is as follows: void MeshResource::setupBeforeRendering() { glEnableVertexAttribArray(0); glEnableVertexAttribArray(1); glEnableVertexAttribArray(2); glEnableVertexAttribArray(3); glEnableVertexAttribArray(4); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, iboID); glBindBuffer(GL_ARRAY_BUFFER, vboID); glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), 0); // Vertex position glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), (const GLvoid*) 12); // Vertex normal glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, sizeof(Vertex), (const GLvoid*) 24); // UV layer 0 glVertexAttribPointer(3, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), (const GLvoid*) 32); // Vertex color glVertexAttribPointer(4, 1, GL_UNSIGNED_SHORT, GL_FALSE, sizeof(Vertex), (const GLvoid*) 44); //Material index } The code that renders the object is this: void MeshResource::render() { glDrawElements(GL_TRIANGLES, geometry->numIndices, GL_UNSIGNED_SHORT, 0); } And the code that cleans up is this: void MeshResource::cleanupAfterRendering() { glDisableVertexAttribArray(0); glDisableVertexAttribArray(1); glDisableVertexAttribArray(2); glDisableVertexAttribArray(3); glDisableVertexAttribArray(4); } The end result of this is that I get a black screen, although the end of my rendering pipeline after the rendering code (essentially just drawing axes and lines on the screen) works properly, so I'm fairly sure it's not an issue with the passing of uniforms. If, however, I change the code slightly so that the rendering code calls the setup immediately before rendering, like so: void MeshResource::render() { setupBeforeRendering(); glDrawElements(GL_TRIANGLES, geometry->numIndices, GL_UNSIGNED_SHORT, 0); } The program works as desired. I don't want to have to do this, though, as my aim is to set up vertex, material, etc. data once per object type and then render each instance updating only the transformation information. The uniformizeModelMatrix works as follows: void RenderManager::uniformizeModelMatrix(Matrix4 matrix) { glBindBuffer(GL_UNIFORM_BUFFER, globalMatrixUBOID); glBufferSubData(GL_UNIFORM_BUFFER, 0, sizeof(Matrix4), matrix.ptr()); glBindBuffer(GL_UNIFORM_BUFFER, 0); }

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  • Getting rid of Massive View Controller in iOS?

    - by Earl Grey
    I had a discussion with my colleague about the following problem. We have an application where we need filtering functionality. On any main screen within the upper navigation bar, there is a button in the upper right corner. Once you touch that button, an custom written Alert View like view will pop up modally, behind it a semitransparent black overlay view. In that modal view, there is a table view of options, and you can choose one exclusively. Based on your selection, once this modal view is closed, the list of items in the main view is filtered. It is simply a modally presented filter to filter the main table view.This UI design is dictated by the design department, I cannot do anything about it so let accept this as a premise. Also the main filter button in the navbar will change colours to indicate that the filter is active. The question I have is about implementation. I suggested to my colleague that we create a separate XYZFilter class that will be an instance created by the main view controller acquire the filtering options handle saving and restoration of its state - i.e. last filter selected provide its two views - the overlay view and the modal view be the datasource for the table in its modal view. For some unknown reason, my colleague was not impressed by that approach at all. He simply wants to do these functionalities in the main view controller, maybe out of being used to do this in the past like that :-/ Is there any fundamental problem with my approach? I want to keep the view controller small, not to have spaghetti code create a reusable component (for use outside the project) have more object oriented, decoupled approach. prevent duplication of code as we need the filtering in two different places but it looks the same in both.. Any advice?

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  • Design suggestions needed to create a MathBuilder framework

    - by Darf Zon
    Let explain what I'm trying to create. I'm creating a framework, the idea is to provide base classes to generate a math problem. Why do I need this framework? Because at first time, I realized when I create a new math problem I always do the same steps. Configuration settings such range numbers. For example if I'm developing multiplications, in beginner level only generate the first number between 2-5 or in advanced level, the first number will be between 6- 9, for example. Generate problem method. All the time I need to invoke a method like this to generate the problem. This one receives the configuration settings and generate the number according to them. And generate the object with the respective data. Validate the problem. Sometimes the problem generated is not valid. For example, supposed I'm creating fractions in most simplified, if I receive 2/4, the program should detect that this is not valid and must generate another like this one, 1/4. Load the view. All of them, have a custom view (please watch below the images). All of the problems must know how to CHECK if the user result is correct. All of this problems has answers. Some of them just require one answer, anothers may require more than one, so I guess a way to maintain flexibility to the developer has all the answers he wanna used. At the beginning I started using PRISM. Generate modules for each math problem was the idea and load it in the main system. I guess are the most important things of this idea. Let me showing some problems which I create in a WPF standalone program. Here I have a math problem about areas. When I generate the problem a set to the view the object and it draw it. In beginner level, I set in the configuration settings that just load square types. But in advance level, can load triangles and squares randomly. In this another, generate a binary problem like addition, subtraction, multiplication or division. Above just generate a single problem. The idea of this is to show a test o quiz, I mean get a worksheet (this I call as a collection of problems) where the user can answer it. I hope gets the idea with my ugly drawing. How to load this math problems? As I said above, I started using PRISM, and each module contains a math problem kind. This is a snapshot of my first demo. Below show the modules loaded, and center the respective configurations or levels. Until momment, I have no idea to start creating this software. I just know that I need a question | problem class, response class, user class. But I get lost about what properties should have to contain in it. Please give a little hand of this framework. I put much effort on this question, so if any isn't clear, let me know to clarify it.

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  • Starting to create a MathBuilder framework, help to start creating the design

    - by Darf Zon
    Let explain what I'm trying to create. I'm creating a framework, the idea is to provide base classes to generate a math problem. Why do I need this framework? Because at first time, I realized when I create a new math problem I always do the same steps. Configuration settings such range numbers. For example if I'm developing multiplications, in beginner level only generate the first number between 2-5 or in advanced level, the first number will be between 6- 9, for example. Generate problem method. All the time I need to invoke a method like this to generate the problem. This one receives the configuration settings and generate the number according to them. And generate the object with the respective data. Validate the problem. Sometimes the problem generated is not valid. For example, supposed I'm creating fractions in most simplified, if I receive 2/4, the program should detect that this is not valid and must generate another like this one, 1/4. Load the view. All of them, have a custom view (please watch below the images). All of the problems must know how to CHECK if the user result is correct. All of this problems has answers. Some of them just require one answer, anothers may require more than one, so I guess a way to maintain flexibility to the developer has all the answers he wanna used. At the beginning I started using PRISM. Generate modules for each math problem was the idea and load it in the main system. I guess are the most important things of this idea. Let me showing some problems which I create in a WPF standalone program. Here I have a math problem about areas. When I generate the problem a set to the view the object and it draw it. In beginner level, I set in the configuration settings that just load square types. But in advance level, can load triangles and squares randomly. In this another, generate a binary problem like addition, subtraction, multiplication or division. Above just generate a single problem. The idea of this is to show a test o quiz, I mean get a worksheet (this I call as a collection of problems) where the user can answer it. I hope gets the idea with my ugly drawing. How to load this math problems? As I said above, I started using PRISM, and each module contains a math problem kind. This is a snapshot of my first demo. Below show the modules loaded, and center the respective configurations or levels. Until momment, I have no idea to start creating this software. I just know that I need a question | problem class, response class, user class. But I get lost about what properties should have to contain in it. Please give a little hand of this framework. I put much effort on this question, so if any isn't clear, let me know to clarify it.

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  • Why is there no service-oriented language?

    - by Wolfgang
    Edit: To avoid further confusion: I am not talking about web services and such. I am talking about structuring applications internally, it's not about how computers communicate. It's about programming languages, compilers and how the imperative programming paradigm is extended. Original: In the imperative programming field, we saw two paradigms in the past 20 years (or more): object-oriented (OO), and service-oriented (SO) aka. component-based (CB). Both paradigms extend the imperative programming paradigm by introducing their own notion of modules. OO calls them objects (and classes) and lets them encapsulates both data (fields) and procedures (methods) together. SO, in contrast, separates data (records, beans, ...) from code (components, services). However, only OO has programming languages which natively support its paradigm: Smalltalk, C++, Java and all other JVM-compatibles, C# and all other .NET-compatibles, Python etc. SO has no such native language. It only comes into existence on top of procedural languages or OO languages: COM/DCOM (binary, C, C++), CORBA, EJB, Spring, Guice (all Java), ... These SO frameworks clearly suffer from the missing native language support of their concepts. They start using OO classes to represent services and records. This leads to designs where there is a clear distinction between classes that have methods only (services) and those that have fields only (records). Inheritance between services or records is then simulated by inheritance of classes. Technically, its not kept so strictly but in general programmers are adviced to make classes to play only one of the two roles. They use additional, external languages to represent the missing parts: IDL's, XML configurations, Annotations in Java code, or even embedded DSL like in Guice. This is especially needed, but not limited to, since the composition of services is not part of the service code itself. In OO, objects create other objects so there is no need for such facilities but for SO there is because services don't instantiate or configure other services. They establish an inner-platform effect on top of OO (early EJB, CORBA) where the programmer has to write all the code that is needed to "drive" SO. Classes represent only a part of the nature of a service and lots of classes have to be written to form a service together. All that boiler plate is necessary because there is no SO compiler which would do it for the programmer. This is just like some people did it in C for OO when there was no C++. You just pass the record which holds the data of the object as a first parameter to the procedure which is the method. In a OO language this parameter is implicit and the compiler produces all the code that we need for virtual functions etc. For SO, this is clearly missing. Especially the newer frameworks extensively use AOP or introspection to add the missing parts to a OO language. This doesn't bring the necessary language expressiveness but avoids the boiler platform code described in the previous point. Some frameworks use code generation to produce the boiler plate code. Configuration files in XML or annotations in OO code is the source of information for this. Not all of the phenomena that I mentioned above can be attributed to SO but I hope it clearly shows that there is a need for a SO language. Since this paradigm is so popular: why isn't there one? Or maybe there are some academic ones but at least the industry doesn't use one.

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  • What are the disadvantages of self-encapsulation?

    - by Dave Jarvis
    Background Tony Hoare's billion dollar mistake was the invention of null. Subsequently, a lot of code has become riddled with null pointer exceptions (segfaults) when software developers try to use (dereference) uninitialized variables. In 1989, Wirfs-Brock and Wikerson wrote: Direct references to variables severely limit the ability of programmers to re?ne existing classes. The programming conventions described here structure the use of variables to promote reusable designs. We encourage users of all object-oriented languages to follow these conventions. Additionally, we strongly urge designers of object-oriented languages to consider the effects of unrestricted variable references on reusability. Problem A lot of software, especially in Java, but likely in C# and C++, often uses the following pattern: public class SomeClass { private String someAttribute; public SomeClass() { this.someAttribute = "Some Value"; } public void someMethod() { if( this.someAttribute.equals( "Some Value" ) ) { // do something... } } public void setAttribute( String s ) { this.someAttribute = s; } public String getAttribute() { return this.someAttribute; } } Sometimes a band-aid solution is used by checking for null throughout the code base: public void someMethod() { assert this.someAttribute != null; if( this.someAttribute.equals( "Some Value" ) ) { // do something... } } public void anotherMethod() { assert this.someAttribute != null; if( this.someAttribute.equals( "Some Default Value" ) ) { // do something... } } The band-aid does not always avoid the null pointer problem: a race condition exists. The race condition is mitigated using: public void anotherMethod() { String someAttribute = this.someAttribute; assert someAttribute != null; if( someAttribute.equals( "Some Default Value" ) ) { // do something... } } Yet that requires two statements (assignment to local copy and check for null) every time a class-scoped variable is used to ensure it is valid. Self-Encapsulation Ken Auer's Reusability Through Self-Encapsulation (Pattern Languages of Program Design, Addison Wesley, New York, pp. 505-516, 1994) advocated self-encapsulation combined with lazy initialization. The result, in Java, would resemble: public class SomeClass { private String someAttribute; public SomeClass() { setAttribute( "Some Value" ); } public void someMethod() { if( getAttribute().equals( "Some Value" ) ) { // do something... } } public void setAttribute( String s ) { this.someAttribute = s; } public String getAttribute() { String someAttribute = this.someAttribute; if( someAttribute == null ) { setAttribute( createDefaultValue() ); } return someAttribute; } protected String createDefaultValue() { return "Some Default Value"; } } All duplicate checks for null are superfluous: getAttribute() ensures the value is never null at a single location within the containing class. Efficiency arguments should be fairly moot -- modern compilers and virtual machines can inline the code when possible. As long as variables are never referenced directly, this also allows for proper application of the Open-Closed Principle. Question What are the disadvantages of self-encapsulation, if any? (Ideally, I would like to see references to studies that contrast the robustness of similarly complex systems that use and don't use self-encapsulation, as this strikes me as a fairly straightforward testable hypothesis.)

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  • Is my class structure good enough?

    - by Rivten
    So I wanted to try out this challenge on reddit which is mostly about how you structure your data the best you can. I decided to challenge my C++ skills. Here's how I planned this. First, there's the Game class. It deals with time and is the only class main has access to. A game has a Forest. For now, this class does not have a lot of things, only a size and a Factory. Will be put in better use when it will come to SDL-stuff I guess A Factory is the thing that deals with the Game Objects (a.k.a. Trees, Lumberjack and Bears). It has a vector of all GameObjects and a queue of Events which will be managed at the end of one month. A GameObject is an abstract class which can be updated and which can notify the Event Listener The EventListener is a class which handles all the Events of a simulation. It can recieve events from a Game Object and notify the Factory if needed, the latter will manage correctly the event. So, the Tree, Lumberjack and Bear classes all inherits from GameObject. And Sapling and Elder Tree inherits from Tree. Finally, an Event is defined by an event_type enumeration (LUMBERJACK_MAWED, SAPPLING_EVOLUTION, ...) and an event_protagonists union (a GameObject or a pair of GameObject (who killed who ?)). I was quite happy at first with this because it seems quite logic and flexible. But I ended up questionning this structure. Here's why : I dislike the fact that a GameObject need to know about the Factory. Indeed, when a Bear moves somewhere, it needs to know if there's a Lumberjack ! Or it is the Factory which handles places and objects. It would be great if a GameObject could only interact with the EventListener... or maybe it's not that much of a big deal. Wouldn't it be better if I separate the Factory in three vectors ? One for each kind of GameObject. The idea would be to optimize research. If I'm looking do delete a dead lumberjack, I would only have to look in one shorter vector rather than a very long vector. Another problem arises when I want to know if there is any particular object in a given case because I have to look for all the gameObjects and see if they are at the given case. I would tend to think that the other idea would be to use a matrix but then the issue would be that I would have empty cases (and therefore unused space). I don't really know if Sapling and Elder Tree should inherit from Tree. Indeed, a Sapling is a Tree but what about its evolution ? Should I just delete the sapling and say to the factory to create a new Tree at the exact same place ? It doesn't seem natural to me to do so. How could I improve this ? Is the design of an Event quite good ? I've never used unions before in C++ but I didn't have any other ideas about what to use. Well, I hope I have been clear enough. Thank you for taking the time to help me !

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  • Saving custom attributes in NSAttributedString

    - by regulus6633
    I need to add a custom attribute to the selected text in an NSTextView. So I can do that by getting the attributed string for the selection, adding a custom attribute to it, and then replacing the selection with my new attributed string. So now I get the text view's attributed string as NSData and write it to a file. Later when I open that file and restore it to the text view my custom attributes are gone! After working out the entire scheme for my custom attribute I find that custom attributes are not saved for you. Look at the IMPORTANT note here: http://developer.apple.com/mac/library/DOCUMENTATION/Cocoa/Conceptual/AttributedStrings/Tasks/RTFAndAttrStrings.html So I have no idea how to save and restore my documents with this custom attribute. Any help?

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  • Custom validator not invoked when using Validation Application Block through configuration

    - by Chris
    I have set up a ruleset in my configuration file which has two validators, one of which is a built-in NotNullValidator, the other of which is a custom validator. The problem is that I see the NotNullValidator hit, but not my custom validator. The custom validator is being used to validate an Entity Framework entity object. I have used the debugger to confirm the NotNull is hit (I forced a failure condition so I saw it set an invalid result), but it never steps into the custom one. I am using MVC as the web app, so I defined the ruleset in a config file at that layer, but my custom validator is defined in another project. However, I wouldn't have thought that to be a problem because when I use the Enterprise Library Configuration tool inside Visual Studio 2008 it is able to set the type properly for the custom validator. As well, I believe the custom validator is fine as it builds ok, and the config tool can reference it properly. Does anybody have any ideas what the problem could be, or even what to do/try to debug further? Here is a stripped down version of my custom validator: [ConfigurationElementType(typeof(CustomValidatorData))] public sealed class UserAccountValidator : Validator { public UserAccountValidator(NameValueCollection attributes) : base(string.Empty, "User Account") { } protected override string DefaultMessageTemplate { get { throw new NotImplementedException(); } } protected override void DoValidate(object objectToValidate, object currentTarget, string key, ValidationResults results) { if (!currentTarget.GetType().Equals(typeof(UserAccount))) { throw new Exception(); } UserAccount userAccountToValidate = (UserAccount)currentTarget; // snipped code ... this.LogValidationResult(results, "The User Account is invalid", currentTarget, key); } } Here is the XML of my ruleset in Validation.config (the NotNull rule is only there to force a failure so I could see it getting hit, and it does): <validation> <type defaultRuleset="default" assemblyName="MyProj.Entities, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" name="MyProj.Entities.UserAccount"> <ruleset name="default"> <properties> <property name="HashedPassword"> <validator negated="true" messageTemplate="" messageTemplateResourceName="" messageTemplateResourceType="" tag="" type="Microsoft.Practices.EnterpriseLibrary.Validation.Validators.NotNullValidator, Microsoft.Practices.EnterpriseLibrary.Validation, Version=4.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" name="Not Null Validator" /> </property> <property name="Property"> <validator messageTemplate="" messageTemplateResourceName="" messageTemplateResourceType="" tag="" type="MyProj.Entities.UserAccountValidator, MyProj.Entities, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" name="Custom Validator" /> </property> </properties> </ruleset> </type> </validation> And here is the stripped down version of the way I invoke the validation: var type = entity.GetType() var validator = ValidationFactory.CreateValidator(type, "default", new FileConfigurationSource("Validation.config")) var results = validator.Validate(entity) Any advice would be much appreciated! Thanks, Chris

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  • Can I set a property on an object that is only declared on the instance type, when I don't know the

    - by WilberBeast
    Let me explain. I have a List into which I am adding various ASP.NET controls. I then wish to loop through the list and set a CssClass, however not every Control supports the property CssClass. What I would like to do is test if the underlying instance type supports the CssClass property and set it, but I'm not sure how to do the conversion prior to setting the property since I don't know the type of each Control object. I know that I can use typeof or x.GetType(), but I'm not sure how to use these to convert the controls back to the instance type in order to test for and then set the property. Actually I seem to have solved this, so I thought that I would post the code here for others. foreach (Control c in controlList) { PropertyInfo pi = c.GetType().GetProperty("CssClass"); if (pi != null) pi.SetValue(c, "desired_css_class", null); } I hope that this helps someone else as I has taken me hours to research these 2 lines of code. Cheers Steve

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  • Why ruby object has two to_s and inspect methods that (looks like) do the same thing?

    - by prosseek
    The p calls inspect, and puts/print calls to_s for representing its object. If I run class Graph def initialize @nodeArray = Array.new @wireArray = Array.new end def to_s # called with print / puts "Graph : #{@nodeArray.size}" end def inspect # called with p "G" end end if __FILE__ == $0 gr = Graph.new p gr print gr puts gr end I get G Graph : 0Graph : 0 Then, why does ruby has two functions do the same thing? What makes the difference between to_s and inspect? And what's the difference between puts/print/p? If I comment out the to_s or inspect function, I get as follows. #<Graph:0x100124b88>#<Graph:0x100124b88>

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  • Java: How do you access a sub-object of an object with no "getXXX" method to that sub-object

    - by Daxon
    I'll explain with pictures from Eclipse Debugger I have an Class called "FieldContext", (I can't edit it, it's compiled in the Java OVal API) Within "FieldContext" on the eclipse variable tab are "CompileTimeType" and "field" Q1 Is there a legend for the icons in the variables tab? like what the red box with the "F" means + yellow diamond boxes? Now I want to access the fields inside the "field" object (RedBox) .. preferably "name" But the "FieldContext" does not have a "getField()" method, yet it has a "getCompileTimeType()" method. Q2 So is there anyway to get that field object being a "SerializableField" Class from the "FieldContext"? If eclipse debugger can see/get/edit them then I hope I can do the same in Java.

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  • Filtering custom fields on wordpress admin page

    - by Kyril
    I'm currently working on a wordpress 2.9.2 plugin (my first) that creates additional custom fields that will later be read from the template. The plugin adds an additional meta box to the "Edit Post" screen which is responsible for manipulating these values. My problem is that the custom fields generated by the plugin also show up in the "Custom Fields" box. Ideally I would like for the custom fields generated by the plugin to be managed separately from any other custom fields for that same post/page. Is there a way that I can filter fields specific to my plugin to prevent them from being displayed in the "Custom Fields" box? I have yet to locate any action or filter that will let me capture and manipulate those values before they are rendered on "Edit Post".

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  • How to get elements from an object in C#?

    - by Drew
    I am using the AutoCompleteBox in WPF, I populate the suggestions with a List that consists of four fields. When the user selects an item and I reach my eventHandler, i can see that MyAutoCompleteBox.SelectedItem is an object that has my four values, if i hover this text in the debugger i can see the four values listed, however i don't know how to access these values in the code. I tried List<Codes> selected = MyAutoCompleteBox.SelectedItem as List<Codes>; where Codes is my List. selected returns as null and empty every time. Is there a way to get to these values? Thanks!

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  • How should I implement items that are normalized in the Database, in Object Oriented Design?

    - by Jonas
    How should I implement items that are normalized in the Database, in Object Oriented classes? In the database I have a big table of items and a smaller of groups. Each item belong to one group. This is how my database design look like: +----------------------------------------+ | Inventory | +----+------+-------+----------+---------+ | Id | Name | Price | Quantity | GroupId | +----+------+-------+----------+---------+ | 43 | Box | 34.00 | 456 | 4 | | 56 | Ball | 56.50 | 3 | 6 | | 66 | Tin | 23.00 | 14 | 4 | +----+------+-------+----------+---------+ Totally 3000 lines +----------------------+ | Groups | +---------+------+-----+ | GroupId | Name | VAT | +---------+------+-----+ | 4 | Mini | 0.2 | | 6 | Big | 0.3 | +---------+------+-----+ Totally 10 lines I will use the OOP classes in a GUI, where the user can edit Items and Groups in the inventory. It should also be easy to do calculations with a bunch of items. The group information like VAT are needed for the calculations. I will write an Item class, but do I need a Group class? and if I need it, should I keep them in a global location or how do I access it when I need it for Item-calculations? Is there any design pattern for this case?

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