MVC C# - Simplest Possible Implementation

Question

My first try of MVC. Am trying to implement a simple example. Inspiration from here. Have I got this pattern (yet!)?

1. View: "Hey, controller, the user just told me he wants the first person"

2. Controller: "Hmm, having checked his credentials, he is allowed to do that... Hey, model, I want you to get me the first person"

3. Model: "First person... got it. Back to you, Controller."

4. Controller: "Here, I'll collect the new set of data. Back to you, view."

5. View: "Cool, I'll show the first person to the user now."

View:

namespace WinFormMVC
{
    public partial class Form1 : Form
    {
        controller cont = new controller();

        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            textBox1.Text = cont.checkPermissionsAndGetFirstPerson();
        }
    }
}

Controller:

public class controller
    {
        public string checkPermissionsAndGetFirstPerson()
        {
            string returnValue = "";
            if (checkPermissions())
            {
                model m = new model();
                returnValue =  m.getFirstPerson();
            }

            return returnValue;

        }

        public bool checkPermissions()
        {
            return true;
        }
    }

Model:

public class model
    {
        public string getFirstPerson()
        {
            return "Bill Smith";
        }
    }

Answer 1

Hmm... I am not sure if I'd call this MVC... As with ASP.NET WebForm, this form is more like an MVP pattern.

As per my understanding, in MVC, controller is the one responsible for managing all resources and flow of the code. In your example, you basically creating a Windows Form first (the view) and then attach a controller to it which is more of a MVP sort of things.

In a classical MVC pattern, the Model, once instantiated, will be linked to the View and when the model changes, the view will get notified (possibly through Observer / PubSub pattern).

Button click, etc. from the View will be routed to the controller which will coordinate those sort of stuffs.

see: this.

Answer 2

I would describe MVC more like this:

1. Request (MVC url routing, some event passed from previous UI etc)

2. Controller - check credentials, get data, return Model

3. Model - represents the data passed back from the Controller

4. View - render the Model returned by the Controller. Depending on the Model may display UI to initialise new Controller actions. May also pass Model back to next Controller action.

I think it can be a little confused because in many Model implementations (such as Linq) they provide data definition and access, but it's still the Controller that knows where to start (even if it's the Model that knows how to save its own changes).

So, your code should be something like:

//Controller:
public class PersonController
{
    public PersonAction Detail(int personId)
    {
        Person returnValue;
        //get person from DB and populate returnValue
        return new PersonAction( returnValue );
    }
}

//Model:
public class Person
{
    public string FirstName {get; set;}
    public string LastName {get; set;}
}

//View:
public partial class PersonDetailView : MVCForm<Person>
{
    public Form1( Person model ):base(model) {
        textBox1.Text = model.FirstName + " " + model.LastName;
    }

    private void button1_Click(object sender, EventArgs e)
    {
        textBox1.Text = model.FirstName + " " + model.LastName;
    }
}

What this example is missing is the framework that makes this all possible - there are two significant parts to that:

1. Something that takes/parses parameters and based on that calls a controller's action method. For instance in Asp.net MVC this is the routing handlers - the call above would be the request url: ~/Person/Detail/personId

2. Something that takes the result from the action (PersonAction in the example above) and finds the correct view to display. In this example it would open a PersonDetailView form and pass the Person model to it.

There are lots of example frameworks for an MVC implementation for WinForms - one of them may be a good starting point.

Answer 3

To adopt the MVC pattern you want to implement the following:

• The view hooks up to the Model and listens for changes.
• The controller hooks up to the view and handles specific events i.e. button presses etc
• The model processes requests made by the controller and notifies the view.

I agree with Jimmy you would want to integrate something like the Observer pattern to this type of system so its possible for the Model to inform the View when it changes so the View can then update itself accordingly.

The difference with MVP is it introduces a Presenter class which monitors the Model on behalf of the View, in other words the View doesn't know about the Model, it only knows about its Presenter. The Presenter responds to changes in the Model and updates the View accordingly.

Answer 4

I think there are a few corrections to be made to your narrative. Strinctly speaking the view does not contact the controller, the user contacts the controller directly. In a web app it looks like this.

1. User: Hey web app, can I have the resource at /people/1

2. Routing engine: That means you person controller. get the first user.

3. User controller: Model, I need you to get me user record for the authenticated user, and the person record for the first person.

4. User Controller: Right. I know the authenticated user is an admin, and person one does exist. So return the Admin view for person to the user.

5. Rendering engine: Build up the html from the view (template) and person object (data)

This is difficult to do in webforms. I guess the best way is to have a page for each controller, and have that page dynamiclly choose and display a user control. One for each view. It is important in MVC that the view is dumb. All requests are handled directly by controllers, which then select which view to use.

Answer 5

Your checkPermissionsAndGetFirstPerson method is probably doing too much. Authorization and fetching data should probably be separate operations.

Also, if your Form1 class is your view, it probably shouldn't be constructing the controller. That seems backwards.

Most information you'll find on MVC in .NET will be for ASP.NET MVC web applications. You might want to check out the WinFormsMVC project on CodePlex to see how someone else has tackled this problem.

http://winformsmvc.codeplex.com/

Here's another WinForms MVC implementation on CodePlex. Looks like it's got a bit more documentation.

http://koosserymvcwin.codeplex.com/

Answer 6

You might find this tutorial very helpful: http://nerddinnerbook.s3.amazonaws.com/Intro.htm. Written by Scott Guthrie, it explains the MVC workflow very well. Part 4 should have the basics you're looking for.