enable drop targets if ItemsControl are in ItemsControl and the ItemsControl is empty

Author: punker76

Examples/DefaultsExample/MainWindow.xaml

@@ -1307,5 +1307,40 @@
         </ListBox>
       </Grid>
     </TabItem>
+
+    <TabItem Header="List in List Example">
+      <Grid>
+        <Grid.ColumnDefinitions>
+          <ColumnDefinition />
+          <ColumnDefinition />
+        </Grid.ColumnDefinitions>
+
+        <ItemsControl Grid.Column="0"
+                      ItemsSource="{Binding Collection1}"
+                      dd:DragDrop.IsDragSource="True"
+                      dd:DragDrop.UseDefaultDragAdorner="True">
+        </ItemsControl>
+
+        <ListBox Grid.Column="1" x:Name="outer">
+          <Border BorderThickness="1" BorderBrush="Black">
+            <ListBox Height="200" Width="200" x:Name="inner1" Background="Aquamarine"
+                 ItemsSource="{Binding Collection2}"
+                 dd:DragDrop.IsDragSource="True"
+                 dd:DragDrop.IsDropTarget="True"
+                 dd:DragDrop.UseDefaultDragAdorner="True">
+            </ListBox>
+          </Border>
+          <Border BorderThickness="1" BorderBrush="Black">
+            <ListBox Height="200" Width="200" x:Name="inner2"
+                 dd:DragDrop.IsDragSource="True"
+                 dd:DragDrop.IsDropTarget="True"
+                 dd:DragDrop.UseDefaultDragAdorner="True">
+              <ListBoxItem Content="Test1"></ListBoxItem>
+            </ListBox>
+          </Border>
+        </ListBox>
+
+      </Grid>
+    </TabItem>
   </TabControl>
 </Window>

GongSolutions.Wpf.DragDrop/DropInfo.cs

@@ -67,6 +67,8 @@ public DropInfo(object sender, DragEventArgs e, DragInfo dragInfo)
 
       if (this.VisualTarget is ItemsControl) {
         var itemsControl = (ItemsControl)this.VisualTarget;
+        //System.Diagnostics.Debug.WriteLine(">>> Name = {0}", itemsControl.Name);
+        // get item under the mouse
         item = itemsControl.GetItemContainerAt(this.DropPosition);
         var directlyOverItem = item != null;
 
@@ -75,6 +77,7 @@ public DropInfo(object sender, DragEventArgs e, DragInfo dragInfo)
         this.VisualTargetFlowDirection = itemsControl.GetItemsPanelFlowDirection();
 
         if (item == null) {
+          // ok, no item found, so maybe we can found an item at top, left, right or bottom
           item = itemsControl.GetItemContainerAt(this.DropPosition, this.VisualTargetOrientation);
           directlyOverItem = false;
         }
@@ -89,7 +92,8 @@ public DropInfo(object sender, DragEventArgs e, DragInfo dragInfo)
           }
         }
 
-        if (item != null) {
+        if (item != null)
+        {
           itemParent = ItemsControl.ItemsControlFromItemContainer(item);
 
           this.InsertIndex = itemParent.ItemContainerGenerator.IndexFromContainer(item);

GongSolutions.Wpf.DragDrop/Utilities/ItemsControlExtensions.cs

@@ -82,7 +82,7 @@ public static UIElement GetItemContainer(this ItemsControl itemsControl, UIEleme
       if (itemType != null) {
         return isItemContainer
                  ? (UIElement)child.GetVisualAncestor(itemType, itemsControl)
-                 : (UIElement)child.GetVisualAncestor(itemType);
+                 : (UIElement)child.GetVisualAncestor(itemType, itemsControl.GetType());
       }
 
       return null;
@@ -123,7 +123,7 @@ public static UIElement GetItemContainerAt(this ItemsControl itemsControl, Point
                                result => {
                                  var itemContainer = isItemContainer
                                                        ? result.VisualHit.GetVisualAncestor(itemContainerType, itemsControl)
-                                                       : result.VisualHit.GetVisualAncestor(itemContainerType);
+                                                       : result.VisualHit.GetVisualAncestor(itemContainerType, itemsControl.GetType());
                                  if (itemContainer != null && !hits.Contains(itemContainer) && ((UIElement)itemContainer).IsVisible == true) {
                                    hits.Add(itemContainer);
                                  }

GongSolutions.Wpf.DragDrop/Utilities/VisualTreeExtensions.cs

@@ -68,15 +68,24 @@ public static T GetVisualAncestor<T>(this DependencyObject d) where T : class
       return null;
     }
 
-    public static DependencyObject GetVisualAncestor(this DependencyObject d, Type type)
+    /// <summary>
+    /// find the visual ancestor item by type
+    /// </summary>
+    public static DependencyObject GetVisualAncestor(this DependencyObject d, Type itemSearchType, Type itemContainerSearchType)
     {
-      var item = VisualTreeHelper.GetParent(d.FindVisualTreeRoot());
+      var currentVisual = VisualTreeHelper.GetParent(d.FindVisualTreeRoot());
 
-      while (item != null && type != null) {
-        if (item.GetType() == type || item.GetType().IsSubclassOf(type)) {
-          return item;
+      while (currentVisual != null && itemSearchType != null) {
+        var currentVisualType = currentVisual.GetType();
+        if (currentVisualType == itemSearchType || currentVisualType.IsSubclassOf(itemSearchType)) {
+          return currentVisual;
         }
-        item = VisualTreeHelper.GetParent(item);
+        if (itemContainerSearchType != null && itemContainerSearchType.IsAssignableFrom(currentVisualType))
+        {
+          // ok, we found an ItemsControl (maybe an empty)
+          return null;
+        }
+        currentVisual = VisualTreeHelper.GetParent(currentVisual);
       }
 
       return null;
@@ -85,16 +94,16 @@ public static DependencyObject GetVisualAncestor(this DependencyObject d, Type t
     /// <summary>
     /// find the visual ancestor by type and go through the visual tree until the given itemsControl will be found
     /// </summary>
-    public static DependencyObject GetVisualAncestor(this DependencyObject d, Type type, ItemsControl itemsControl)
+    public static DependencyObject GetVisualAncestor(this DependencyObject d, Type itemSearchType, ItemsControl itemsControl)
     {
       var item = VisualTreeHelper.GetParent(d.FindVisualTreeRoot());
       DependencyObject lastFoundItemByType = null;
 
-      while (item != null && type != null) {
+      while (item != null && itemSearchType != null) {
         if (item == itemsControl) {
           return lastFoundItemByType;
         }
-        if ((item.GetType() == type || item.GetType().IsSubclassOf(type))
+        if ((item.GetType() == itemSearchType || item.GetType().IsSubclassOf(itemSearchType))
             && (itemsControl == null || itemsControl.ItemContainerGenerator.IndexFromContainer(item) != -1)) {
           lastFoundItemByType = item;
         }