How to properly implement MVC using C#.NET in Windows Forms Applications

Question

I've been looking all over the web for example implementations of an MVC setup in .NET. I have found many examples but they all seem to differ in certain aspects. I have a book on Design Patterns that described that MVC was originated in Smalltalk so I read over several people discussing its implementation in that language. What follows is an example project I wrote utilizing what I gathered was a proper implementation but I've been confused by a few details.

One problem I run into is the proper order of the construction of the objects. Here is the impl in my Program.cs

Model mdl = new Model();
Controller ctrl = new Controller(mdl);
Application.Run(new Form1(ctrl, mdl));

The View: Immediately I have a couple of issues I'm unsure of. First, if the view is supposed to only read data from the Model for updating, but contains a reference to it, what is stopping me from making the calls the controller does to the model from the view? Should a programmer just ignore the fact that they are exposed to the models member functions? Another thought I had, was perhaps the event that informs the view the model is updated, would send some sort of state object for the view to update itself with.

public interface IView
{
    double TopSpeed { get; }
    double ZeroTo60 { get; }

    int VehicleID { get; }
    string VehicleName { get; }
}

/// <summary>
/// Assume the form has the following controls
/// A button with a click event OnSaveClicked
/// A combobox with a selected index changed event OnSelectedIndexChanged
/// A textbox that displays the vehicles top speed named mTextTopSpeed
/// A textbox that displays the vehicles zero to 60 time named mTextZeroTo60
/// </summary>

public partial class Form1 : Form, IView
{
    private IController mController;
    private IModel mModel;

    public Form1(IController controller, IModel model)
    {
        InitializeComponent();

        mController = controller;
        mController.SetListener(this);
        mModel = model;
        mModel.ModelChanged += new ModelUpdated(mModel_ModelChanged);
    }

    void mModel_ModelChanged(object sender, EventArgs e)
    {
        mTextTopSpeed.Text = mModel.TopSpeed.ToString();
        mTextZeroTo60.Text = mModel.ZeroTo60.ToString();
    }

    public double TopSpeed { get { return Double.Parse(mTextTopSpeed.Text); } }

    public double ZeroTo60 { get { return Double.Parse(mTextZeroTo60.Text); } }

    public int VehicleID { get { return (int)mComboVehicles.SelectedValue; } }

    public string VehicleName { get { return mComboVehicles.SelectedText; } }

    #region Form Events

    private void OnFormLoad(object sender, EventArgs e)
    {
        mComboVehicles.ValueMember = "Key";
        mComboVehicles.DisplayMember = "Value";
        mComboVehicles.DataSource = new BindingSource(mModel.VehicleList, null);
    }

    private void OnSelectedIndexChanged(object sender, EventArgs e)
    {
        mController.OnSelectedVehicleChanged();
    }

    private void OnSaveClicked(object sender, EventArgs e)
    {
        mController.OnUpdateVehicle();
    }

    #endregion
}

The Controller: My only real issue with the way I have implemented the controller is that it seems a bit odd to me that is possible to construct the controller without definitely having a view assigned to it. I could ignore the view entirely but that would mean I would pass parameters to the controller's functions for updating the model which seems to miss the point entirely.

public interface IController
{
    void OnUpdateVehicle();
    void OnSelectedVehicleChanged();
    void SetListener(IView view);
}

class Controller : IController
{
    private IModel mModel;
    private IView mView = null;

    public Controller(IModel model)
    {
        mModel = model;
    }

    public void OnUpdateVehicle()
    {
        if(mView == null)
            return;

        mModel.UpdateVehicle(mView.VehicleID, mView.TopSpeed, mView.ZeroTo60);
    }

    public void SetListener(IView view)
    {
        mView = view;
    }

    public void OnSelectedVehicleChanged()
    {
        if (mView == null)
            return;
        mModel.SelectVehicle(mView.VehicleID);
    }
}

The Model: In my form, I have a combobox that is a list of the vehicles given in my pseudo database. I feel as though my form should actually implement multiple Views / Models because of this. A view specific to listing the possible vehicles with a corresponding controller / model, and a view for displaying information about the selected vehicle with its own controller / model.

public delegate void ModelUpdated(object sender, EventArgs e);

public interface IModel
{
    event ModelUpdated ModelChanged;

    void UpdateVehicle(int id, double topSpeed, double zeroTo60);
    void SelectVehicle(int id);

    double TopSpeed { get; }
    double ZeroTo60 { get; }
    IDictionary<int, string> VehicleList { get; }
}

// class for the sake of a pseudo database object
class Vehicle
{
    public int ID { get; set; }
    public string Name { get; set; }
    public double TopSpeed { get; set; }
    public double ZeroTo60 { get; set; }

    public Vehicle(int id, string name, double topSpeed, double zeroTo60)
    {
        ID = id;
        Name = name;
        TopSpeed = topSpeed;
        ZeroTo60 = zeroTo60;
    }
}


class Model : IModel
{
    private List<Vehicle> mVehicles = new List<Vehicle>()
    {
        new Vehicle(1, "Civic", 120.0, 5.0),
        new Vehicle(2, "Batmobile", 9000.0, 1.0),
        new Vehicle(3, "Tricycle", 5.0, 0.0)
    };

    private Vehicle mCurrentVehicle;

    public Model()
    {
        mCurrentVehicle = mVehicles[0];
    }

    public event ModelUpdated ModelChanged;

    public void OnModelChanged()
    {
        if (ModelChanged != null)
        {
            ModelChanged(this, new EventArgs());
        }
    }

    public double TopSpeed { get { return mCurrentVehicle.TopSpeed; } }

    public double ZeroTo60 { get { return mCurrentVehicle.ZeroTo60; } }

    public IDictionary<int, string> VehicleList
    {
        get 
        {
            Dictionary<int, string> vDict = new Dictionary<int, string>();
            foreach (Vehicle v in mVehicles)
            {
                vDict.Add(v.ID, v.Name);
            }

            return vDict as IDictionary<int, string>;
        }
    }

    #region Pseudo Database Calls

    public void SelectVehicle(int id)
    {
        foreach (Vehicle v in mVehicles)
        {
            if (v.ID == id)
            {
                mCurrentVehicle = v;
                OnModelChanged(); // send notification to registered views
                break;
            }
        }
    }

    public void UpdateVehicle(int id, double topSpeed, double zeroTo60)
    {
        foreach (Vehicle v in mVehicles)
        {
            if (v.ID == id)
            {
                mCurrentVehicle.TopSpeed = topSpeed;
                mCurrentVehicle.ZeroTo60 = zeroTo60;
                OnModelChanged(); // send notification to registered views
                break;
            }
        }
    }

    #endregion
}

In Conclusion of this tl;dr, I guess what I'm looking for, is some guidance on whether or not what I'm doing here represents a true MVC implementation and maybe for someone to shed some light on the aforementioned concerns. Any advice would be greatly appreciated.

Answer 1

We'll it depends on what you want to do. You currently have an implementation of the Supervising Controller. If you wish to remove the model from the view (and any databinding), you can implement a Passive View pattern instead. See this article for more differences.

_{(source: microsoft.com)}

And Martin Fowler is king (GUI Architectures).