Merge pull request #872 from daserge/wpf-treeview-shift-tab-crash

[WPF] Fixes a crash for ArrowUp into treeview without selected row

Xwt.WPF/Xwt.WPFBackend/ExTreeView.cs

@@ -313,6 +313,9 @@ namespace Xwt.WPFBackend
 
 		public void SelectItem(ExTreeViewItem item)
 		{
+			if (item == null)
+				return;
+
 			FocusItem(item);
 			if (!CtrlPressed)
 				SelectedItems.Clear();
@@ -450,7 +453,12 @@ namespace Xwt.WPFBackend
 			int indexOfP = items.IndexOf(p);
 			if (indexOfP == 0)
 				return p;
-			else
+			else if (indexOfP == -1) {
+				if (items.Count > 0)
+					return items [items.Count - 1];
+
+				return null;
+ 			} else
 				return items[indexOfP - 1];
 		}
 

Xwt.WPF/Xwt.WPFBackend/ExTreeViewItem.cs

@@ -57,6 +57,9 @@ namespace Xwt.WPFBackend
 
 		protected override void OnExpanded (RoutedEventArgs e)
 		{
+			if (!(DataContext is TreeStoreNode))
+				return;
+
 			var node = (TreeStoreNode)DataContext;
 			view.Backend.Context.InvokeUserCode (delegate {
 				((ITreeViewEventSink)view.Backend.EventSink).OnRowExpanding (node);
@@ -71,10 +74,10 @@ namespace Xwt.WPFBackend
 
 		protected override void OnCollapsed(RoutedEventArgs e)
 		{
-			var node = DataContext as TreeStoreNode;
-			if (node == null) {
-				return;
-			}
+			if (!(DataContext is TreeStoreNode))
+				return;
+
+			var node = (TreeStoreNode)DataContext;
 			if (!IsExpanded)
 				UnselectChildren((object o, ExTreeViewItem i) =>
 				{