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  • how to share a variable between two threads

    - by prmatta
    I just inherited some code, two threads within this code need to perform a system task. One thread should do the system task before the other thread. They should not be performing the system task together. The two threads do not have references to each other. Now, I know I can use some sort of a semaphore to achieve this. But my question is what is the right way to get both threads to access this semaphore. I could create a static variable/method a new class : public class SharedSemaphore { private static Semaphore s = new Semaphore (1, true); public static void performSystemTask () { s.acquire(); } public static void donePerformingSystemTask() { s.release(); } } This would work (right?) but this doesn't seem like the right thing to do. Because, the threads now have access to a semaphore, without ever having a reference to it. This sort of thing doesn't seem like a good programming practice. Am I wrong?

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  • .net design pattern question

    - by user359562
    Hi. I am trying to understand design pattern problems. I am trying to modify the code like this in winforms and trying to see if any design pattern suits my requirement. Please suggest which is the best design pattern in this scenario. This is very basic code containing 2 tab pages which might have different controls can be added dynamically and read out different files on click of particular tab. To elaborate more... I have written this code to learn and understand design pattern. This is just a scenario where user click on a particular tab which will show dynamic controls generated. public partial class Form1 : Form { public Form1() { InitializeComponent(); } private void tabControl1_SelectedIndexChanged(object sender, EventArgs e) { if (tabControl1.SelectedTab.Name.Equals("tabPage1")) { GeneratedynamicControlsForTab1(); } else if (tabControl1.SelectedTab.Name.Equals("tabPage2")) { GeneratedynamicControlsForTab2(); } } private void GeneratedynamicControlsForTab1() { Label label1 = new Label(); label1.Text = "Label1"; tabPage1.Controls.Add(label1); ReadCSVFile(); } private void GeneratedynamicControlsForTab2() { tabPage1.Controls.Clear(); Label label2 = new Label(); label2.Text = "Label2"; tabPage2.Controls.Add(label2); ReadTextFile(); } private void ReadCSVFile() { } private void ReadTextFile() { } }

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  • How can I handle multiple views of a data object? Which design pattern is acceptable?

    - by tranquil.byte
    I have a person object. class Person { private $name; ... } I need to be able to change how they are displayed on the front-end ( visitors have control ). They can choose list view, grid view, photo view for example. class PersonDisplay { public function displayList() { // Query database // Output html to display in list mode } public function displayPhoto() { // Query database // Output html to display in photo mode } } Is this an acceptable way to handle the presentation of the items on the front-end or is there a specific design pattern I should be researching to help me with this task? Does anyone have any suggestions or ideas where this could go wrong or if this could potentially make maintenance a nightmare? The Person object was just an example very similiar to what I am using.

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  • Is this physical collection class that contains only static methods an Anti-Pattern?

    - by Tj Kellie
    I'm trying to figure out if I should continue on with a current pattern in an application I'm working in, or refactor this into something else. I have a set of collection classes off a generic base of List. These classes have public constructors but contain only static methods that return collections. They look like this: public class UserObjCollection : BaseCollection<UserObj> { public static UserObjCollection GetAllUserObj() { UserObjCollection obj = new UserObjCollection(); obj.MapObjects(new UserObjDataService().GetAllUserObj()); return obj; } } Is this a Pattern or Anti-Pattern and what are the merits of this over a straight factory pattern?

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  • Java: Make a method abstract for each extending class

    - by Martijn Courteaux
    Hi, Is there any keyword or design pattern for doing this? public abstract class Root { public abstract void foo(); } public abstract class SubClass extends Root { public void foo() { // Do something } } public class SubberClass extends SubClass { // Here is it not necessary to override foo() // So is there a way to make this necessary? // A way to obligate the developer make again the override } Thanks

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  • Undo/Redo using Memento: Stack, Queue or just LinkedList?

    - by serhio
    What is the best having when implementing Memento pattern (for Undo/Redo) in witch collection to Keep Mementos? Basically, I need this(c = change, u = undo, r = redo): 0 *c -1 0 *c -2 -1 0 *c -3 -2 -1 0 <u -2 -1 0 1 *c -3 -2 -1 0 Variants: LinkedList - possible in principle, maybe not optimized. Queue - not adapted for this task, IMO. Stack - not adapted for undo AND redo; Double Stack - maybe optimal, but can't control the undo maximum size.

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  • Looking for design help

    - by jess
    I have this scenario in most of the WindowsForms having grids I have a sequence of code which is similar - AddNewRow(in grid),CreateNewEntity,notifyUser,few other steps Now, I want to use a template kind of pattern.But,my issue is with CreateEntity method since sometimes it is passed a parameter which is different depending on the type of object being created.Should I make createentity accept an "object" type,and cast when the parameter is to be used.What other way can I tackle this design issue? Also,CreateEntity returns the object being created.

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  • Should I create protected constructor for my singleton classes?

    - by Vijay Shanker
    By design, in Singleton pattern the constructor should be marked private and provide a creational method retuning the private static member of the same type instance. I have created my singleton classes like this only. public class SingletonPattern {// singleton class private static SingletonPattern pattern = new SingletonPattern(); private SingletonPattern() { } public static SingletonPattern getInstance() { return pattern; } } Now, I have got to extend a singleton class to add new behaviors. But the private constructor is not letting be define the child class. I was thinking to change the default constructor to protected constructor for the singleton base class. What can be problems, if I define my constructors to be protected? Looking for expert views....

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  • Visitor Pattern can be replaced with Callback functions?

    - by getit
    Is there any significant benefit to using either technique? In case there are variations, the Visitor Pattern I mean is this: http://en.wikipedia.org/wiki/Visitor_pattern And below is an example of using a delegate to achieve the same effect (at least I think it is the same) Say there is a collection of nested elements: Schools contain Departments which contain Students Instead of using the Visitor pattern to perform something on each collection item, why not use a simple callback (Action delegate in C#) Say something like this class Department { List Students; } class School { List Departments; VisitStudents(Action<Student> actionDelegate) { foreach(var dep in this.Departments) { foreach(var stu in dep.Students) { actionDelegate(stu); } } } } School A = new School(); ...//populate collections A.Visit((student)=> { ...Do Something with student... }); *EDIT Example with delegate accepting multiple params Say I wanted to pass both the student and department, I could modify the Action definition like so: Action class School { List Departments; VisitStudents(Action<Student, Department> actionDelegate, Action<Department> d2) { foreach(var dep in this.Departments) { d2(dep); //This performs a different process. //Using Visitor pattern would avoid having to keep adding new delegates. //This looks like the main benefit so far foreach(var stu in dep.Students) { actionDelegate(stu, dep); } } } }

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  • Proper design a Model-Controller in Cocoa?

    - by legege
    Hi, I'm trying to design a simple Cocoa application and I would like to have a clear and easy to understand software architecture. Of course, I'm using a basic MVC design and my question concerns the Model layer. For my application, the Model represents data fetched on the Internet with a XML-RPC API. I'm planning to use Core Data to represent a locally fetched version. How should the data be loaded initially? I'm reading the Cocoa Design Pattern book, and they talk about a Model-Controller that is centric to the Model. How would that be done? Thanks!

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  • Process a batch of items, return an object to report on status

    - by Naeem Sarfraz
    I'm looking for a pattern (or good practice) for the following scenario: My function List<BatchItemResponse> Process(List<BatchItem> Data) {..} will process a list of data, and return info on where each item in the batch could be processed. struct BatchItemResponse { int BatchItemID; bool Processed; string Description; } Any thoughts? Is what I've proposed as good as it gets?

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  • Should I create subclass NSManagedObject or not?

    - by TP
    Hi, I have spent a few days learning and writing NSCoding and finally got it working. However, it took very long to archive and unarchive the (quite complex) object graph, which is unacceptable. After searching the internet for some time, I think the better way is to use core data. Do you recommend that 1) I should rewrite all my classes as subclasses of NSManagedObject or 2) should I create an instance variable of NSManagedObject in each of my class so that any changes to the class also updates its core data representation? Doing either way will need significant changes to the exiting classes and I think I have to update lots of unit test cases as well if it changes the way the classes are initialized. What do you recommend? I really don't want to head to the wrong approach again... Thanks!

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  • Process for beginning a Ruby on Rails project

    - by Daniel Beardsley
    I'm about to begin a Ruby on Rails project and I'd love to hear how others go through the process of starting an application design. I have quite a bit of experience with RoR, but don't have that many starting from scratch with only a vision experiences and would appreciate the wisdom of others who've been there. I'm looking for an order of events, reasons for the order, and maybe why each part is important. I can think of a few starting points, but I'm not sure where it's best to begin Model design and relationships (entities, how they relate, and their attributes) Think of user use-cases (or story-boards) and implement the minimum to get these done Create Model unit-tests then create the necessary migrations and AR models to get the tests to pass Hack out the most basic version of the simplest part of your application and go from there Start with a template for a rails app (like http://github.com/thoughtbot/suspenders) Do the boring gruntwork first (User auth, session management, ...) ...

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  • WPF binding to a boolean on a control

    - by Jose
    I'm wondering if someone has a simple succinct solution to binding to a dependency property that needs to be the converse of the property. Here's an example I have a textbox that is disabled based on a property in the datacontext e.g.: <TextBox IsEnabled={Binding CanEdit} Text={Binding MyText}/> The requirement changes and I want to make it ReadOnly instead of disabled, so without changing my ViewModel I could do this: In the UserControl resources: <UserControl.Resources> <m:NotConverter x:Key="NotConverter"/> </UserControl.Resources> And then change the TextBox to: <TextBox IsReadOnly={Binding CanEdit,Converter={StaticResource NotConverter}} Text={Binding MyText}/> Which I personally think is EXTREMELY verbose I would love to be able to just do this(notice the !): <TextBox IsReadOnly={Binding !CanEdit} Text={Binding MyText}/> But alas, that is not an option that I know of. I can think of two options. Create an attached property IsNotReadOnly to FrameworkElement(?) and bind to that property If I change my ViewModel then I could add a property CanEdit and another CannotEdit which I would be kind of embarrassed of because I believe it adds an irrelevant property to a class, which I don't think is a good practice. The main reason for the question is that in my project the above isn't just for one control, so trying to keep my project as DRY as possible and readable I am throwing this out to anyone feeling my pain and has come up with a solution :)

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  • Explain "Leader/Follower" Pattern

    - by Alex B
    I can't seem to find a good explanation of "Leader/Follower" pattern. All explanations either simply refer to it in the context of some problem, or are completely meaningless. Can anyone explain to the the mechanics of how this pattern works, and why and how it improves performance over more traditional asynchronous IO models? Examples and links to diagrams are appreciated too.

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  • Implementing the procducer-consumer pattern with .NET 4.0

    - by bitbonk
    With alle the new paralell programming features in .NET 4.0, what would be a a simple and fast way to implement the producer-consumer pattern (where at least one thread is producing/enqueuing task items and another thread executes/dequeues these tasks). Can we benfit from all these new APIs? What is your preferred implementation of this pattern?

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  • .Net - Whats the difference between a Session Facade and Business Delegate?

    - by KP65
    What I understand so far: Business Delegate - In the presentation tier, as an ASP component, provides an interface for ASP views to access business components without exposing their API, therefore reducing coupling between the two. Session Facade - In the business tier, as a com+ component, encapsulates business objects, provides a course grain interface for views to access business components. Reduces coupling, hides complex business component interaction from views. So what is the actual difference? They seem pretty similar to me..

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  • anti-if campaign

    - by Andrew Siemer
    I recently ran against a very interesting site that expresses a very interesting idea - the anti-if campaign. You can see this here at www.antiifcampaign.com. I have to agree that complex nested IF statements are an absolute pain in the rear. I am currently on a project that up until very recently had some crazy nested IFs that scrolled to the right for quite a ways. We cured our issues in two ways - we used Windows Workflow Foundation to address routing (or workflow) concerns. And we are in the process of implementing all of our business rules utilizing ILOG Rules for .NET (recently purchased by IBM!!). This for the most part has cured our nested IF pains...but I find myself wondering how many people cure their pains in the manner that the good folks at the AntiIfCampaign suggest (see an example here) by creating numerous amounts of abstract classes to represent a given scenario that was originally covered by the nested IF. I wonder if another way to address the removal of this complexity might also be in using an IoC container such as StructureMap to move in and out of different bits of functionality. Either way... Question: Given a scenario where I have a nested complex IF or SWITCH statement that is used to evaluate a given type of thing (say evaluating an Enum) to determine how I want to handle the processing of that thing by enum type - what are some ways to do the same form of processing without using the IF or SWITCH hierarchical structure? public enum WidgetTypes { Type1, Type2, Type3, Type4 } ... WidgetTypes _myType = WidgetTypes.Type1; ... switch(_myType) { case WidgetTypes.Type1: //do something break; case WidgetTypes.Type2: //do something break; //etc... }

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  • When are global variables acceptable?

    - by dsimcha
    Everyone here seems to hate global variables, but I see at least one very reasonable use for them: They are great for holding program parameters that are determined at program initialization and not modified afterwords. Do you agree that this is an exception to the "globals are evil" rule? Is there any other exception that you can think of, besides in quick and dirty throwaway code where basically anything goes? If not, why are globals so fundamentally evil that you do not believe that there are any exceptons?

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  • Regarding the ViewModel

    - by mizipzor
    Im struggling to understand the ViewModel part of the MVVM pattern. My current approach is to have a class, with no logic whatsoever (important), except that it implements INotifyPropertyChanged. The class is just a collection of properties, a struct if you like, describing an as small part of the data as possible. I consider this my Model. Most of the WPF code I write are settings dialogs that configure said Model. The code-behind of the dialog exposes a property which returns an instance of the Model. In the XAML code I bind to subproperties of that property, thereby binding directly to the Model's properties. Which works quite well since it implements the INotifyPropertyChanged. I consider this settings dialog the View. However, I havent really been able to figure out what in all this is the ViewModel. The articles Ive read suggests that the ViewModel should tie the View and the Model together, providing the logic the Model lacks but is still to complex to go directly into the View. Is this correct? Would, in my example, the code-behind of the settings dialog be considered the ViewModel? I just feel a bit lost and would like my peers to debunk some of my assumptions. Am I completely off track here?

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  • Pattern for creating a database schema using JDBC

    - by Space_C0wb0y
    I have a Java-application that loads data from a legacy file format into an SQLite-Database using JDBC. If the database file specified does not exist, it is supposed to create a new one. Currently the schema for the database is hardcoded in the application. I would much rather have it in a separate file as an SQL-Script, but apparently there is now easy way to execute an SQL-Script though JDBC. Is there any other way or a pattern to achieve something like this?

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  • Observer pattern and violation of Single Responsibility Principle

    - by Devil Jin
    I have an applet which repaints itself once the text has changed Design 1: //MyApplet.java public class MyApplet extends Applet implements Listener{ private DynamicText text = null; public void init(){ text = new DynamicText("Welcome"); } public void paint(Graphics g){ g.drawString(text.getText(), 50, 30); } //implement Listener update() method public void update(){ repaint(); } } //DynamicText.java public class DynamicText implements Publisher{ // implements Publisher interface methods //notify listeners whenever text changes } Isn't this a violation of Single Responsibility Principle where my Applet not only acts as Applet but also has to do Listener job. Same way DynamicText class not only generates the dynamic text but updates the registered listeners. Design 2: //MyApplet.java public class MyApplet extends Applet{ private AppletListener appLstnr = null; public void init(){ appLstnr = new AppletListener(this); // applet stuff } } // AppletListener.java public class AppletListener implements Listener{ private Applet applet = null; public AppletListener(Applet applet){ this.applet = applet; } public void update(){ this.applet.repaint(); } } // DynamicText public class DynamicText{ private TextPublisher textPblshr = null; public DynamicText(TextPublisher txtPblshr){ this.textPblshr = txtPblshr; } // call textPblshr.notifyListeners whenever text changes } public class TextPublisher implments Publisher{ // implements publisher interface methods } Q1. Is design 1 a SPR violation? Q2. Is composition a better choice here to remove SPR violation as in design 2.

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