Wiring View, Model and Presenter dynamically, by convention / reflection

Question

I'm trying to develop an application using the MVP pattern.

The problem is wiring all the code manually. I was hoping to reduce the code needed. I tried to copy another solution, but I couldn't get to work. I'm using Winforms and the solution I was using as source is using WPF.

It would wire things on some conventions:

View events are wired by name. For example:"Loaded" event on the view will be wired to the "OnLoaded()" method on the presenter Button commands are wired by name. For example: MoveNext" button is wired to the "OnMoveNext()" method. Grids double click is wired by name. For example: Double click on "Actions" will be wired to the "OnActionsChoosen(ToDoAction)"

The working code in WPF is:

    private static void WireListBoxesDoubleClick(IPresenter presenter)
    {
        var presenterType = presenter.GetType();
        var methodsAndListBoxes = from method in GetActionMethods(presenterType)
                                  where method.Name.EndsWith("Choosen")
                                  where method.GetParameters().Length == 1
                                  let elementName = method.Name.Substring(2, method.Name.Length - 2 /*On*/- 7 /*Choosen*/)
                                  let matchingListBox = LogicalTreeHelper.FindLogicalNode(presenter.View, elementName) as ListBox
                                  where matchingListBox != null
                                  select new {method, matchingListBox};

        foreach (var methodAndEvent in methodsAndListBoxes)
        {
            var parameterType = methodAndEvent.method.GetParameters()[0].ParameterType;
            var action = Delegate.CreateDelegate(typeof(Action<>).MakeGenericType(parameterType),
                                                 presenter, methodAndEvent.method);

            methodAndEvent.matchingListBox.MouseDoubleClick += (sender, args) =>
            {
                var item1 = ((ListBox)sender).SelectedItem;
                if(item1 == null)
                    return;
                action.DynamicInvoke(item1);
            };
        }   
    }

    private static void WireEvents(IPresenter presenter)
    {
        var viewType = presenter.View.GetType();
        var presenterType = presenter.GetType();
        var methodsAndEvents =
                from method in GetParameterlessActionMethods(presenterType)
                let matchingEvent = viewType.GetEvent(method.Name.Substring(2))
                where matchingEvent != null
                where matchingEvent.EventHandlerType == typeof(RoutedEventHandler)
                select new { method, matchingEvent };

        foreach (var methodAndEvent in methodsAndEvents)
        {
            var action = (Action)Delegate.CreateDelegate(typeof(Action),
                                                          presenter, methodAndEvent.method);

            var handler = (RoutedEventHandler)((sender, args) => action());
            methodAndEvent.matchingEvent.AddEventHandler(presenter.View, handler);
        }
    }

    private static IEnumerable<MethodInfo> GetActionMethods(Type type)
    {
        return from method in type.GetMethods(BindingFlags.DeclaredOnly | BindingFlags.Public | BindingFlags.Instance)
               where method.Name.StartsWith("On")
               select method;
    }

    private static IEnumerable<MethodInfo> GetParameterlessActionMethods(Type type)
    {
        return from method in GetActionMethods(type)
               where method.GetParameters().Length == 0
               select method;
    }

Anyway, I tried to port that to a WinForm app, but I wasn't successful. I changed the RoutedEventHandlers to EventHandlers , but couldn't find what to do about the LogicalTreeHelper .

I'm kind of stuck on this. I could do manually but I found this mini-framework so ingenuous that it's almost crazy.

PS: Source is http://msdn.microsoft.com/en-us/magazine/ee819139.aspx

Edit

I just realized something. I'm not gone dumb, the code above is not very test friendly, is it?

Answer 1

Ok. I got it working myself. I'm just posting the answer because at lest one other person found interesting.

First, the view

public interface IBaseView
{
    void Show();
    C Get<C>(string controlName) where C : Control; //Needed to later wire the events
}

public interface IView : IBaseView
{
    TextBox ClientId { get; set; } //Need to expose this
    Button SaveClient { get; set; }
    ListBox MyLittleList { get; set; }
}

public partial class View : Form, IView
{
    public TextBox ClientId //since I'm exposing it, my "concrete view" the controls are camelCased
    {
        get { return this.clientId; }
        set { this.clientId = value; }
    }

    public Button SaveClient
    {
        get { return this.saveClient; }
        set { this.saveClient = value; }
    }

    public ListBox MyLittleList
    {
        get { return this.myLittleList; }
        set { this.myLittleList = value; }
    }

    //The view must also return the control to be wired.
    public C Get<C>(string ControlName) where C : Control
    {
        var controlName = ControlName.ToLower();
        var underlyingControlName = controlName[0] + ControlName.Substring(1);
        var underlyingControl = this.Controls.Find(underlyingControlName, true).FirstOrDefault();
        //It is strange because is turning PascalCase to camelCase. Could've used _Control for the controls on the concrete view instead
        return underlyingControl as C;
    }

Now the Presenter:

public class Presenter : BasePresenter <ViewModel, View>
{
    Client client;
    IView view;
    ViewModel viewModel;

    public Presenter(int clientId, IView viewParam, ViewModel viewModelParam)
    {
        this.view = viewParam;
        this.viewModel = viewModelParam;

        client = viewModel.FindById(clientId);
        BindData(client);
        wireEventsTo(view); //Implement on the base class
    }

    public void OnSaveClient(object sender, EventArgs e)
    {
        viewModel.Save(client);
    }

    public void OnEnter(object sender, EventArgs e)
    {
        MessageBox.Show("It works!");
    }

    public void OnMyLittleListChanged(object sender, EventArgs e)
    {
        MessageBox.Show("Test");
    }
}

The "magic" happens at the base class. In the wireEventsTo(IBaseView view)

public abstract class BasePresenter
    <VM, V>
    where VM : BaseViewModel
    where V : IBaseView, new()
{

    protected void wireEventsTo(IBaseView view)
    {
        Type presenterType = this.GetType();
        Type viewType = view.GetType();

        foreach (var method in presenterType.GetMethods())
        {
            var methodName = method.Name;

            if (methodName.StartsWith("On"))
            {
                try
                {
                    var presenterMethodName = methodName.Substring(2);
                    var nameOfMemberToMatch = presenterMethodName.Replace("Changed", ""); //ListBoxes wiring

                    var matchingMember = viewType.GetMember(nameOfMemberToMatch).FirstOrDefault();

                    if (matchingMember == null)
                    {
                        return;
                    }

                    if (matchingMember.MemberType == MemberTypes.Event)
                    {
                        wireMethod(view, matchingMember, method);    
                    }

                    if (matchingMember.MemberType == MemberTypes.Property)
                    {
                        wireMember(view, matchingMember, method);    
                    }

                }
                catch (Exception ex)
                {
                    continue;
                }
            }
        }
    }

    private void wireMember(IBaseView view, MemberInfo match, MethodInfo method)
    {
        var matchingMemberType = ((PropertyInfo)match).PropertyType;

        if (matchingMemberType == typeof(Button))
        {
            var matchingButton = view.Get<Button>(match.Name);

            var eventHandler = (EventHandler)EventHandler.CreateDelegate(typeof(EventHandler), this, method);

            matchingButton.Click += eventHandler;
        }

        if (matchingMemberType == typeof(ListBox))
        {
            var matchinListBox = view.Get<ListBox>(match.Name);

            var eventHandler = (EventHandler)EventHandler.CreateDelegate(typeof(EventHandler), this, method);

            matchinListBox.SelectedIndexChanged += eventHandler;
        }
    }

    private void wireMethod(IBaseView view, MemberInfo match, MethodInfo method)
    {
        var viewType = view.GetType();

        var matchingEvent = viewType.GetEvent(match.Name);

        if (matchingEvent != null)
        {
            if (matchingEvent.EventHandlerType == typeof(EventHandler))
            {
               var eventHandler = EventHandler.CreateDelegate(typeof(EventHandler), this, method);
               matchingEvent.AddEventHandler(view, eventHandler);
            }

            if (matchingEvent.EventHandlerType == typeof(FormClosedEventHandler))
            {
                var eventHandler = FormClosedEventHandler.CreateDelegate(typeof(FormClosedEventHandler), this, method);
                matchingEvent.AddEventHandler(view, eventHandler);
            }
        }
    }
}

I've got this working here as it is. It will autowire the EventHandler on the Presenter to the Default Events of the Controls that are on IView.

Also, on a side note, I want to share the BindData method.

    protected void BindData(Client client)
    {
        string nameOfPropertyBeingReferenced; 

        nameOfPropertyBeingReferenced = MVP.Controller.GetPropertyName(() => client.Id);
        view.ClientId.BindTo(client, nameOfPropertyBeingReferenced);

        nameOfPropertyBeingReferenced = MVP.Controller.GetPropertyName(() => client.FullName);
        view.ClientName.BindTo(client, nameOfPropertyBeingReferenced);
    }

    public static void BindTo(this TextBox thisTextBox, object viewModelObject, string nameOfPropertyBeingReferenced)
    {
        Bind(viewModelObject, thisTextBox, nameOfPropertyBeingReferenced, "Text");
    }

    private static void Bind(object sourceObject, Control destinationControl, string sourceObjectMember, string destinationControlMember)
    {
        Binding binding = new Binding(destinationControlMember, sourceObject, sourceObjectMember, true, DataSourceUpdateMode.OnPropertyChanged);
        //Binding binding = new Binding(sourceObjectMember, sourceObject, destinationControlMember);
        destinationControl.DataBindings.Clear();
        destinationControl.DataBindings.Add(binding);
    }

    public static string GetPropertyName<T>(Expression<Func<T>> exp)
    {
        return (((MemberExpression)(exp.Body)).Member).Name;
    }

This eliminates "magic strings" from the Binding. I think it can also be used on INotificationPropertyChanged.

Anyway, I hope someone finds it useful. And I completely ok if you want to point out code smells.