Make the TestApplication work again.

Expose the tab item content selector from TabControl, and make
FuncMemberSelector return default(T) if the parameter is of the wrong
type.

samples/TestApplication/GalleryStyle.cs

@@ -107,13 +107,10 @@ namespace TestApplication
                     new Deck
                     {
                         Name = "deck",
-                        DataTemplates = new DataTemplates
+                        MemberSelector = control.ContentSelector,
-                        {
-                            new DataTemplate<TabItem>(x => (Control)control.MaterializeDataTemplate(x.Content)),
-                        },
                         [~Deck.TransitionProperty] = control[~TabControl.TransitionProperty],
-                        [!ItemsControl.ItemsProperty] = control[!ItemsControl.ItemsProperty],
+                        [!Deck.ItemsProperty] = control[!ItemsControl.ItemsProperty],
-                        [!SelectingItemsControl.SelectedItemProperty] = control[!SelectingItemsControl.SelectedItemProperty],
+                        [!Deck.SelectedItemProperty] = control[!SelectingItemsControl.SelectedItemProperty],
                         [Grid.ColumnProperty] = 1,
                     }
                 }

src/Perspex.Controls/TabControl.cs

@@ -4,6 +4,7 @@
 using Perspex.Animation;
 using Perspex.Controls.Presenters;
 using Perspex.Controls.Primitives;
+using Perspex.Controls.Templates;
 
 namespace Perspex.Controls
 {
@@ -24,6 +25,9 @@ namespace Perspex.Controls
         public static readonly PerspexProperty<IPageTransition> TransitionProperty =
             Deck.TransitionProperty.AddOwner<TabControl>();
 
+        private static readonly IMemberSelector s_contentSelector =
+            new FuncMemberSelector<object, object>(SelectContent);
+
         /// <summary>
         /// Initializes static members of the <see cref="TabControl"/> class.
         /// </summary>
@@ -34,6 +38,14 @@ namespace Perspex.Controls
             SelectedIndexProperty.Changed.AddClassHandler<TabControl>(x => x.SelectedIndexChanged);
         }
 
+        /// <summary>
+        /// Gets an <see cref="IMemberSelector"/> that selects the content of a <see cref="TabItem"/>.
+        /// </summary>
+        public IMemberSelector ContentSelector
+        {
+            get { return s_contentSelector; }
+        }
+
         /// <summary>
         /// Gets the <see cref="SelectingItemsControl.SelectedItem"/> as a <see cref="TabItem"/>.
         /// </summary>
@@ -65,6 +77,25 @@ namespace Perspex.Controls
             return control is DeckPresenter;
         }
 
+        /// <summary>
+        /// Selects the content of a tab item.
+        /// </summary>
+        /// <param name="o">The tab item.</param>
+        /// <returns>The content.</returns>
+        private static object SelectContent(object o)
+        {
+            var content = o as IContentControl;
+
+            if (content != null)
+            {
+                return content.Content;
+            }
+            else
+            {
+                return o;
+            }       
+        }
+
         /// <summary>
         /// Called when the <see cref="SelectingItemsControl.SelectedIndex"/> property changes.
         /// </summary>

src/Perspex.Controls/Templates/FuncMemberSelector.cs

@@ -29,7 +29,7 @@ namespace Perspex.Controls.Templates
         /// <returns>The selected member.</returns>
         public object Select(object o)
         {
-            return (o is TObject) ? _selector((TObject)o) : o;
+            return (o is TObject) ? _selector((TObject)o) : default(TMember);
         }
     }
 }

tests/Perspex.Controls.UnitTests/TabControlTests.cs

@@ -187,7 +187,7 @@ namespace Perspex.Controls.UnitTests
                     {
                         Name = "deck",
                         Template = new ControlTemplate<Deck>(CreateDeckTemplate),
-                        MemberSelector = new FuncMemberSelector<TabItem, object>(x => x.Content),
+                        MemberSelector = parent.ContentSelector,
                         [!ItemsControl.ItemsProperty] = parent[!ItemsControl.ItemsProperty],
                         [!SelectingItemsControl.SelectedItemProperty] = parent[!SelectingItemsControl.SelectedItemProperty],
                     }