Make DataContext a part of the IView

We need to set the ViewModel via DataContext, otherwise WPF won't
trigger binding events, so make DataContext a part of the IView, and
make sure ViewModel is not readonly.
Also, make ViewModel typed, no reason for it to be object.

Author: shana

src/GitHub.App/Controllers/UIController.cs

@@ -688,13 +688,13 @@ bool CreateViewAndViewModel(UIViewType viewType)
             {
                 var d = list[viewType];
                 if (d.View.ViewModel == null)
-                    d.View.ViewModel = d.ViewModel;
+                    d.View.DataContext = d.ViewModel;
             }
 
             if (!list.ContainsKey(viewType))
             {
                 var d = factory.CreateViewAndViewModel(viewType);
-                d.View.ViewModel = d.ViewModel;
+                d.View.DataContext = d.ViewModel;
                 list.Add(viewType, d);
                 return true;
             }

src/GitHub.App/Factories/UIFactory.cs

@@ -33,9 +33,7 @@ public UIFactory(IExportFactoryProvider factory)
         /// <returns>true if the View/ViewModel didn't exist and had to be created</returns>
         public IUIPair CreateViewAndViewModel(UIViewType viewType)
         {
-            var d = new UIPair(viewType, factory.GetView(viewType), factory.GetViewModel(viewType));
-            d.View.ViewModel = d.ViewModel;
-            return d;
+            return new UIPair(viewType, factory.GetView(viewType), factory.GetViewModel(viewType));
         }
     }
 

src/GitHub.Exports/UI/IView.cs

@@ -1,13 +1,17 @@
-using System;
+using GitHub.ViewModels;
+using System;
 
 namespace GitHub.UI
 {
     public interface IView
     {
-        object ViewModel { get; set; }
+        IViewModel ViewModel { get; }
         IObservable<object> Done { get; }
         IObservable<object> Cancel { get; }
         IObservable<bool> IsBusy { get; }
+        // necessary for WPF to trigger binding events
+        object DataContext { get; set; }
+
     }
 
     public interface IHasDetailView

src/GitHub.UI.Reactive/Controls/SimpleViewUserControl.cs

@@ -89,7 +89,8 @@ public void Dispose()
     }
 
     public class SimpleViewUserControl<TViewModel, TImplementor> : SimpleViewUserControl, IViewFor<TViewModel>, IView 
-        where TViewModel : class, IViewModel where TImplementor : class
+        where TViewModel : class, IViewModel
+        where TImplementor : class
     {
         public static readonly DependencyProperty ViewModelProperty = DependencyProperty.Register(
             "ViewModel", typeof(TViewModel), typeof(TImplementor), new PropertyMetadata(null));
@@ -103,11 +104,10 @@ object IViewFor.ViewModel
         }
 
         [AllowNull]
-        object IView.ViewModel
+        IViewModel IView.ViewModel
         {
             [return: AllowNull]
             get { return ViewModel; }
-            set { ViewModel = (TViewModel)value; }
         }
 
         [AllowNull]

src/GitHub.VisualStudio/UI/GitHubPane.cs

@@ -39,11 +39,6 @@ IView View
             get { return Content as IView; }
             set { Content = value; }
         }
-        IViewModel ViewModel
-        {
-            get { return (Content as UserControl).DataContext as IViewModel; }
-            set { (Content as UserControl).DataContext = value; }
-        }
 
         [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
         public GitHubPane() : base(null)
@@ -64,20 +59,20 @@ public GitHubPane() : base(null)
             var d = factory.CreateViewAndViewModel(Exports.UIViewType.GitHubPane);
             // placeholder logic to load the view until the UIController is able to do it for us
             View = d.View;
-            ViewModel = d.ViewModel;
+            View.DataContext = d.ViewModel;
         }
 
         protected override void Initialize()
         {
             base.Initialize();
-            var vm = (Content as IView).ViewModel as IServiceProviderAware;
+            var vm = View.ViewModel as IServiceProviderAware;
             Debug.Assert(vm != null);
             vm?.Initialize(this);
         }
 
         public void ShowView(ViewWithData data)
         {
-            ViewModel?.Initialize(data);
+            View.ViewModel?.Initialize(data);
         }
 
         [return: AllowNull]