Fix for #9: NullReferenceException when SelectTab called with no tabbed pages or tab pages cleared.

Author: Michael Pham

src/NativeCode.Mobile.AppCompat.Renderers/Renderers/AppCompatButtonRenderer.cs

@@ -26,7 +26,8 @@ protected override void OnElementChanged(ElementChangedEventArgs<Button> e)
             // in the base method.
             if (this.Control == null)
             {
-                var control = new AppCompatButton(this.Context.GetAppCompatThemedContext());
+                var context = this.Context.GetAppCompatThemedContext();
+                var control = new AppCompatButton(context);
                 this.SetNativeControl(control);
 
                 control.SetOnClickListener(ButtonClickListener.Instance);

src/NativeCode.Mobile.AppCompat.Renderers/Renderers/AppCompatEntryRenderer.cs

@@ -67,7 +67,8 @@ protected override void OnElementChanged(ElementChangedEventArgs<Entry> e)
 
             if (e.OldElement == null)
             {
-                var control = new AppCompatEntryEditText(this.Context.GetAppCompatThemedContext());
+                var context = this.Context.GetAppCompatThemedContext();
+                var control = new AppCompatEntryEditText(context);
                 this.SetNativeControl(control);
 
                 this.Control.ImeOptions = ImeAction.Done;

src/NativeCode.Mobile.AppCompat.Renderers/Renderers/AppCompatSwitchRenderer.cs

@@ -85,7 +85,8 @@ protected override void OnElementChanged(ElementChangedEventArgs<Switch> e)
 
             if (this.Control == null)
             {
-                var control = new SwitchCompat(this.Context.GetAppCompatThemedContext());
+                var context = this.Context.GetAppCompatThemedContext();
+                var control = new SwitchCompat(context);
                 control.SetOnCheckedChangeListener(this);
                 this.SetNativeControl(control);
             }

src/NativeCode.Mobile.AppCompat/FormsAppCompat/Adapters/ActionBarAdapter.cs

@@ -182,7 +182,10 @@ public override void RemoveTab(Tab tab)
         [Obsolete("Will be removed in a future version.", false)]
         public override void SelectTab(Tab tab)
         {
-            this.SupportActionBar.SelectTab(((TabAdapter)tab).SupportTab);
+            if (tab != null)
+            {
+                this.SupportActionBar.SelectTab(((TabAdapter)tab).SupportTab);
+            }
         }
 
         [Obsolete("Will be removed in a future version.", false)]