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    <p>I'm using an attached property for this, and then use that property in my xaml file to change the background color of the tree view item:</p> <pre><code>using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Windows; using System.Windows.Controls; using System.Windows.Input; namespace SKNotes.Utilities { /// &lt;summary&gt; /// Implements an attached property used for styling TreeViewItems when /// they're a possible drop target. /// &lt;/summary&gt; public static class TreeViewDropHighlighter { #region private variables /// &lt;summary&gt; /// the TreeViewItem that is the current drop target /// &lt;/summary&gt; private static TreeViewItem _currentItem = null; /// &lt;summary&gt; /// Indicates whether the current TreeViewItem is a possible /// drop target /// &lt;/summary&gt; private static bool _dropPossible; #endregion #region IsPossibleDropTarget /// &lt;summary&gt; /// Property key (since this is a read-only DP) for the IsPossibleDropTarget property. /// &lt;/summary&gt; private static readonly DependencyPropertyKey IsPossibleDropTargetKey = DependencyProperty.RegisterAttachedReadOnly( "IsPossibleDropTarget", typeof( bool ), typeof( TreeViewDropHighlighter ), new FrameworkPropertyMetadata( null, new CoerceValueCallback( CalculateIsPossibleDropTarget ) ) ); /// &lt;summary&gt; /// Dependency Property IsPossibleDropTarget. /// Is true if the TreeViewItem is a possible drop target (i.e., if it would receive /// the OnDrop event if the mouse button is released right now). /// &lt;/summary&gt; public static readonly DependencyProperty IsPossibleDropTargetProperty = IsPossibleDropTargetKey.DependencyProperty; /// &lt;summary&gt; /// Getter for IsPossibleDropTarget /// &lt;/summary&gt; public static bool GetIsPossibleDropTarget( DependencyObject obj ) { return (bool)obj.GetValue( IsPossibleDropTargetProperty ); } /// &lt;summary&gt; /// Coercion method which calculates the IsPossibleDropTarget property. /// &lt;/summary&gt; private static object CalculateIsPossibleDropTarget( DependencyObject item, object value ) { if ( ( item == _currentItem ) &amp;&amp; ( _dropPossible ) ) return true; else return false; } #endregion /// &lt;summary&gt; /// Initializes the &lt;see cref="TreeViewDropHighlighter"/&gt; class. /// &lt;/summary&gt; static TreeViewDropHighlighter( ) { // Get all drag enter/leave events for TreeViewItem. EventManager.RegisterClassHandler( typeof( TreeViewItem ), TreeViewItem.PreviewDragEnterEvent, new DragEventHandler( OnDragEvent ), true ); EventManager.RegisterClassHandler( typeof( TreeViewItem ), TreeViewItem.PreviewDragLeaveEvent, new DragEventHandler( OnDragLeave ), true ); EventManager.RegisterClassHandler( typeof( TreeViewItem ), TreeViewItem.PreviewDragOverEvent, new DragEventHandler( OnDragEvent ), true ); } #region event handlers /// &lt;summary&gt; /// Called when an item is dragged over the TreeViewItem. /// &lt;/summary&gt; /// &lt;param name="sender"&gt;The sender.&lt;/param&gt; /// &lt;param name="args"&gt;The &lt;see cref="System.Windows.DragEventArgs"/&gt; instance containing the event data.&lt;/param&gt; static void OnDragEvent( object sender, DragEventArgs args ) { lock ( IsPossibleDropTargetProperty ) { _dropPossible = false; if ( _currentItem != null ) { // Tell the item that previously had the mouse that it no longer does. DependencyObject oldItem = _currentItem; _currentItem = null; oldItem.InvalidateProperty( IsPossibleDropTargetProperty ); } if ( args.Effects != DragDropEffects.None ) { _dropPossible = true; } TreeViewItem tvi = sender as TreeViewItem; if ( tvi != null ) { _currentItem = tvi; // Tell that item to re-calculate the IsPossibleDropTarget property _currentItem.InvalidateProperty( IsPossibleDropTargetProperty ); } } } /// &lt;summary&gt; /// Called when the drag cursor leaves the TreeViewItem /// &lt;/summary&gt; /// &lt;param name="sender"&gt;The sender.&lt;/param&gt; /// &lt;param name="args"&gt;The &lt;see cref="System.Windows.DragEventArgs"/&gt; instance containing the event data.&lt;/param&gt; static void OnDragLeave( object sender, DragEventArgs args ) { lock ( IsPossibleDropTargetProperty ) { _dropPossible = false; if ( _currentItem != null ) { // Tell the item that previously had the mouse that it no longer does. DependencyObject oldItem = _currentItem; _currentItem = null; oldItem.InvalidateProperty( IsPossibleDropTargetProperty ); } TreeViewItem tvi = sender as TreeViewItem; if ( tvi != null ) { _currentItem = tvi; tvi.InvalidateProperty( IsPossibleDropTargetProperty ); } } } #endregion } } </code></pre> <p>and then in the xaml file:</p> <pre><code> &lt;TreeView.ItemContainerStyle&gt; &lt;Style TargetType="{x:Type TreeViewItem}"&gt; &lt;Setter Property="FontWeight" Value="Normal" /&gt; &lt;Style.Triggers&gt; &lt;Trigger Property="utils:TreeViewDropHighlighter.IsPossibleDropTarget" Value="True"&gt; &lt;Setter Property="Background" Value="{DynamicResource {x:Static SystemColors.HighlightBrushKey}}" /&gt; &lt;/Trigger&gt; &lt;/Style.Triggers&gt; &lt;/Style&gt; &lt;/TreeView.ItemContainerStyle&gt; </code></pre>
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    1. COThat is a beautiful thing, thank you so much!
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    2. COThis is exactly what I needed today. Thanks so much Stefan! In my treeview I noticed though that sometimes it wouldn't automatically remove the highlight from my drop, so I registered the drop event and wrote a simple function that sets _dropPossible back to false and Invalidates IsPossibleDropTargetProperty. Maybe useful to somebody else?
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    3. COGreat work! One thing that I added in addition to what #chocojosh added, is telling the TreeViewItem to expand if it has items on the OnDragEvent event. You can do this by adding: if (_currentItem.HasItems) _currentItem.IsExpanded = true;
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