Grouping insertion adorner fix

GongSolutions.Wpf.DragDrop/DragInfo.cs

@@ -3,6 +3,7 @@
 using System.Linq;
 using System.Windows;
 using System.Windows.Controls;
+using System.Windows.Data;
 using System.Windows.Input;
 using GongSolutions.Wpf.DragDrop.Utilities;
 
@@ -40,6 +41,7 @@ public DragInfo(object sender, MouseButtonEventArgs e)
       if (sender is ItemsControl) {
         var itemsControl = (ItemsControl)sender;
 
+        this.SourceGroup = itemsControl.FindGroup(this.DragStartPosition);
         this.VisualSourceFlowDirection = itemsControl.GetItemsPanelFlowDirection();
 
         var sourceItem = e.OriginalSource as UIElement; // If we can't cast object as a UIElement it might be a FrameworkContentElement, if so try and use its parent.
@@ -159,6 +161,11 @@ public DragInfo(object sender, MouseButtonEventArgs e)
     /// </remarks>
     public IEnumerable SourceItems { get; private set; }
 
+    /// <summary>
+    /// Gets the group from a dragged item if the drag is currently from an ItemsControl with groups.
+    /// </summary>
+    public CollectionViewGroup SourceGroup { get; private set; }
+
     /// <summary>
     /// Gets the control that initiated the drag.
     /// </summary>

GongSolutions.Wpf.DragDrop/DropInfo.cs

@@ -60,7 +60,7 @@ public DropInfo(object sender, DragEventArgs e, DragInfo dragInfo)
         var item = itemsControl.GetItemContainerAt(this.DropPosition);
         var directlyOverItem = item != null;
 
-        this.TargetGroup = this.FindGroup(itemsControl, this.DropPosition);
+        this.TargetGroup = itemsControl.FindGroup(this.DropPosition);
         this.VisualTargetOrientation = itemsControl.GetItemsPanelOrientation();
         this.VisualTargetFlowDirection = itemsControl.GetItemsPanelFlowDirection();
 
@@ -122,21 +122,6 @@ public DropInfo(object sender, DragEventArgs e, DragInfo dragInfo)
       }
     }
 
-    private CollectionViewGroup FindGroup(ItemsControl itemsControl, Point position)
-    {
-      var element = itemsControl.InputHitTest(position) as DependencyObject;
-
-      if (element != null) {
-        var groupItem = element.GetVisualAncestor<GroupItem>();
-
-        if (groupItem != null) {
-          return groupItem.Content as CollectionViewGroup;
-        }
-      }
-
-      return null;
-    }
-
     /// <summary>
     /// Gets the drag data.
     /// </summary>

GongSolutions.Wpf.DragDrop/DropTargetInsertionAdorner.cs

@@ -1,8 +1,10 @@
 using System;
 using System.Collections.Generic;
+using System.Collections.ObjectModel;
 using System.Linq;
 using System.Text;
 using System.Windows;
+using System.Windows.Data;
 using System.Windows.Media;
 using System.Windows.Controls;
 using System.Collections;
@@ -33,6 +35,17 @@ protected override void OnRender(DrawingContext drawingContext)
         }
 
         var index = Math.Min(this.DropInfo.InsertIndex, itemParent.Items.Count - 1);
+
+        var lastItemInGroup = false;
+        var targetGroup = this.DropInfo.TargetGroup;
+        if (targetGroup != null && targetGroup.IsBottomLevel && this.DropInfo.InsertPosition.HasFlag(RelativeInsertPosition.AfterTargetItem)) {
+          var indexOf = targetGroup.Items.IndexOf(this.DropInfo.TargetItem);
+          lastItemInGroup = indexOf == targetGroup.ItemCount - 1;
+          if (lastItemInGroup) {
+            index--;
+          }
+        }
+
         var itemContainer = (UIElement)itemParent.ItemContainerGenerator.ContainerFromIndex(index);
 
         if (itemContainer != null) {
@@ -41,7 +54,7 @@ protected override void OnRender(DrawingContext drawingContext)
           double rotation = 0;
 
           if (this.DropInfo.VisualTargetOrientation == Orientation.Vertical) {
-            if (this.DropInfo.InsertIndex == itemParent.Items.Count) {
+            if (this.DropInfo.InsertIndex == itemParent.Items.Count || lastItemInGroup) {
               itemRect.Y += itemContainer.RenderSize.Height;
             }
 

GongSolutions.Wpf.DragDrop/IDragInfo.cs

@@ -1,5 +1,6 @@
 using System.Collections;
 using System.Windows;
+using System.Windows.Data;
 using System.Windows.Input;
 
 namespace GongSolutions.Wpf.DragDrop
@@ -72,6 +73,11 @@ public interface IDragInfo
     /// </remarks>
     IEnumerable SourceItems { get; }
 
+    /// <summary>
+    /// Gets the group from a dragged item if the drag is currently from an ItemsControl with groups.
+    /// </summary>
+    CollectionViewGroup SourceGroup { get; }
+
     /// <summary>
     /// Gets the control that initiated the drag.
     /// </summary>

GongSolutions.Wpf.DragDrop/Utilities/ItemsControlExtensions.cs

@@ -3,6 +3,7 @@
 using System.Linq;
 using System.Windows;
 using System.Windows.Controls;
+using System.Windows.Data;
 using System.Windows.Media;
 using System.Reflection;
 using System.Collections;
@@ -17,6 +18,21 @@ namespace GongSolutions.Wpf.DragDrop.Utilities
 {
   public static class ItemsControlExtensions
   {
+    public static CollectionViewGroup FindGroup(this ItemsControl itemsControl, Point position)
+    {
+      var element = itemsControl.InputHitTest(position) as DependencyObject;
+
+      if (element != null) {
+        var groupItem = element.GetVisualAncestor<GroupItem>();
+
+        if (groupItem != null) {
+          return groupItem.Content as CollectionViewGroup;
+        }
+      }
+
+      return null;
+    }
+
     public static bool CanSelectMultipleItems(this ItemsControl itemsControl)
     {
       if (itemsControl is MultiSelector) {