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POUnderstanding the MVC Pattern
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copied!<p>I am having some trouble understanding the MVC Pattern. I do understand we are trying to decouple the GUI from the business logic, although I'm having problems understanding how.</p> <p>From what I understood, the <code>View</code>, is what the user sees. So it generally is the window/form. The <code>Controller</code> is inbetween the <code>View</code> and the <code>Model</code>. The Controller will make the data "flow" in both directions. It will also persist state when needed (if I have a wizard with 5 steps, it is the <code>Controller</code>'s responsability to ensure they are made in the correct order, etc). The <code>Model,</code> is where the core of my application logic lives.</p> <p>Is this view correct?</p> <p>To try to turn this into something more meaningful, I'll try to sketch out a simple example with WinForms(no ASP.NET or WPF, please! - to the java crowd, from what I come to understand, Swing works in a similar way to WinForms!), to see if I get it right, and I'll raise the questions I always come to while doing it.</p> <hr> <p>Let's assume I have a model that contains just a class (just to make it easier. I know it will make the example look dumb but its easier this way):</p> <pre><code>class MyNumbers { private IList<int> listOfNumbers = new List<int> { 1, 3, 5, 7, 9 }; public IList<int> GetNumbers() { return new ReadOnlyCollection<int>(listOfNumbers); } } </code></pre> <p>Now it's time to make my <code>Controller</code>:</p> <pre><code>class Controller { private MyNumbers myNumbers = new MyNumbers(); public IList<int> GetNumbers() { return myNumbers.GetNumbers(); } } </code></pre> <p>The <code>View</code> should just have a <code>ListBox</code> that has as items all the numbers retrieved in <code>MyNumbers</code>.</p> <h2>Now, the first question arises:</h2> <p>Should the <code>Controller</code> be responsible for creating <code>MyNumbers</code>? In this simple case, I think its acceptable(as <code>MyNumbers</code> will do exactly the same, no matter what, and has no associated state). But let's assume I would want to use for all the different Controllers my app has the same instance of <code>MyNumbers</code>. I would have to pass to this <code>Controller</code>(and all others that need it) that instance of <code>MyNumbers</code> that I want to use. Who is going to be responsible for that? In this WinForms examples, would that be the <code>View</code>? Or would that be the class that creates the <code>View</code>?</p> <p>Turning the question around: what is the order of instantiation of these 3 parts? What is the code that the "owner" of the <code>MVC</code> called to create it? Should the <code>Controller</code> create both the <code>View</code> and <code>Model</code>? Should the <code>View</code> instantiate the <code>Controller</code> and the <code>Controller</code> the <code>Model</code>?</p> <h2>Second question:</h2> <p>How is the <code>main</code> method supposed to look like, assuming I only want my application to have the <code>Use Case</code> this <code>Controller</code> portrays?</p> <h2>Third:</h2> <p>Why does in the following MVC diagram, the <code>View</code> have an arrow to the <code>Model</code>? Shouldn't the <code>Controller</code> be always the bridge between both <code>View</code> and <code>Model</code>?</p> <p><img src="https://upload.wikimedia.org/wikipedia/commons/thumb/b/b5/ModelViewControllerDiagram2.svg/350px-ModelViewControllerDiagram2.svg.png" alt="alt text"></p> <hr> <p>I'll have one or two more questions, but they probably will make more sense asked after I understand this first detail. Or maybe after I understand that first question all the others tear apart.</p> <p>Thanks!</p>

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