Fix DropDown dropping down.

Make clicking on an open DropDown close it, and wire up the ToggleButon.

src/Perspex.Controls/DropDown.cs

@@ -36,6 +36,7 @@ namespace Perspex.Controls
 
         private bool _isDropDownOpen;
         private Popup _popup;
+        private bool _closing;
 
         static DropDown()
         {
@@ -111,15 +112,14 @@ namespace Perspex.Controls
 
         protected override void OnPointerPressed(PointerPressEventArgs e)
         {
-            if (!IsDropDownOpen)
+            if (!IsDropDownOpen && !_closing && ((IVisual)e.Source).GetVisualRoot() != typeof(PopupRoot))
             {
-                if (((IVisual)e.Source).GetVisualAncestors().Last().GetType() != typeof(PopupRoot))
-                {
-                    IsDropDownOpen = true;
-                    e.Handled = true;
-                }
+                IsDropDownOpen = true;
+                e.Handled = true;
             }
 
+            _closing = false;
+
             if (!e.Handled)
             {
                 if (UpdateSelectionFromEventSource(e.Source))
@@ -140,6 +140,7 @@ namespace Perspex.Controls
 
             _popup = e.NameScope.Get<Popup>("PART_Popup");
             _popup.Opened += PopupOpened;
+            _popup.Closed += PopupClosed;
         }
 
         private void PopupOpened(object sender, EventArgs e)
@@ -153,6 +154,11 @@ namespace Perspex.Controls
             }
         }
 
+        private void PopupClosed(object sender, EventArgs e)
+        {
+            _closing = true;
+        }
+
         private void SelectedItemChanged(PerspexPropertyChangedEventArgs e)
         {
             UpdateSelectionBoxItem(e.NewValue);

src/Perspex.Controls/Primitives/Popup.cs

@@ -59,6 +59,7 @@ namespace Perspex.Controls.Primitives
         /// </summary>
         static Popup()
         {
+            IsHitTestVisibleProperty.OverrideDefaultValue<Popup>(false);
             ChildProperty.Changed.AddClassHandler<Popup>(x => x.ChildChanged);
             IsOpenProperty.Changed.AddClassHandler<Popup>(x => x.IsOpenChanged);
         }

src/Perspex.Themes.Default/DropDown.paml

@@ -20,6 +20,7 @@
                           Background="Transparent"
                           ClickMode="Press"
                           Focusable="False"
+                          IsChecked="{TemplateBinding IsDropDownOpen, Mode=TwoWay}"
                           Grid.Column="1">
               <Path Fill="Black"
                     Width="8"