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    <p>This post is simply a porting of Stefan's awesome response above to VB, for those of us working in those confines; I have nothing to offer except to hope I didn't screw anything up too badly. It appears to work for me:</p> <pre><code>Namespace SKNotes.Utilities ''' &lt;summary&gt; ''' Implements an attached property used for styling TreeViewItems when ''' they are a possible drop target. ''' &lt;/summary&gt; Public Class TreeViewDropHighlighter ''' &lt;summary&gt; ''' The TreeViewItem that is the current drop target ''' &lt;/summary&gt; Private Shared _CurrentItem As TreeViewItem = Nothing ''' &lt;summary&gt; ''' Indicates whether the current TreeView Item is a possible drop target ''' &lt;/summary&gt; ''' &lt;remarks&gt;&lt;/remarks&gt; Private Shared _DropPossible As Boolean ''' &lt;summary&gt; ''' Property Key (since this is a read only DP) for the IsPossibleDropTarget property. ''' &lt;/summary&gt; ''' &lt;remarks&gt;&lt;/remarks&gt; Private Shared ReadOnly IsPossibleDropTargetKey As DependencyPropertyKey = _ DependencyProperty.RegisterAttachedReadOnly _ ( _ "IsPossibleDropTarget", _ GetType(Boolean), _ GetType(TreeViewDropHighlighter), _ New FrameworkPropertyMetadata(Nothing, _ New CoerceValueCallback(AddressOf CalculateIsPossibleDropTarget) ) ) ''' &lt;summary&gt; ''' Dependency Property IsPossibleDropTarget. ''' Is true if the TreeViewItem is a possible drop target (ie, if it would receive the ''' OnDrop even if the mouse button is release right now). ''' &lt;/summary&gt; ''' &lt;remarks&gt;&lt;/remarks&gt; Public Shared ReadOnly IsPossibleDropTargetProperty As DependencyProperty = IsPossibleDropTargetKey.DependencyProperty ''' &lt;summary&gt; ''' Getter for IsPossibleDropTarget ''' &lt;/summary&gt; Public Shared Function GetIsPossibleDropTarget(ByVal obj As DependencyObject) As Boolean Return CBool(obj.GetValue(IsPossibleDropTargetProperty)) End Function ''' &lt;summary&gt; ''' Coercion method which calculates the IsPossibleDropTarget property ''' &lt;/summary&gt; Private Shared Function CalculateIsPossibleDropTarget(item As DependencyObject, value As Object) As Object If item.Equals(_CurrentItem) And _ _DropPossible Then Return True Else Return False End If End Function ''' &lt;summary&gt; ''' Initializes the TreeViewDropHighlighter class ''' &lt;/summary&gt; Shared Sub New() EventManager.RegisterClassHandler(GetType(TreeViewItem), _ TreeViewItem.PreviewDragEnterEvent, _ New DragEventHandler(AddressOf OnDragEvent), True) EventManager.RegisterClassHandler(GetType(TreeViewItem), _ TreeViewItem.PreviewDragLeaveEvent, New DragEventHandler(AddressOf OnDragLeave), True) EventManager.RegisterClassHandler(GetType(TreeViewItem), _ TreeViewItem.PreviewDragOverEvent, _ New DragEventHandler(AddressOf OnDragEvent), True) End Sub ''' &lt;summary&gt; ''' Called when an item is dragged over the TreeView Item ''' &lt;/summary&gt; ''' &lt;param name="sender"&gt;The sender&lt;/param&gt; ''' &lt;param name="args"&gt;The System.Windows.DragEventArgs instance containing the event data&lt;/param&gt; ''' &lt;remarks&gt;&lt;/remarks&gt; Shared Sub OnDragEvent(sender As Object, args As DragEventArgs) SyncLock (IsPossibleDropTargetProperty) _DropPossible = False If Not IsNothing(_CurrentItem) Then 'Tell the item that previously had the mouse that it no longer does. Dim OldItem As DependencyObject = _CurrentItem _CurrentItem = Nothing OldItem.InvalidateProperty(IsPossibleDropTargetProperty) End If If args.Effects &lt;&gt; DragDropEffects.None Then _DropPossible = True End If Dim tvi As TreeViewItem = CType(sender, TreeViewItem) If Not IsNothing(tvi) Then _CurrentItem = tvi 'Tell that item to recalculate the IsPossibleDropTarget property _CurrentItem.InvalidateProperty(IsPossibleDropTargetProperty) End If End SyncLock End Sub Shared Sub OnDragLeave(sender As Object, args As DragEventArgs) SyncLock (IsPossibleDropTargetProperty) _DropPossible = False If Not IsNothing(_CurrentItem) Then 'Tell the item that previously had the mouse that it no longer does Dim OldItem As DependencyObject = _CurrentItem _CurrentItem = Nothing OldItem.InvalidateProperty(IsPossibleDropTargetProperty) End If Dim tvi As TreeViewItem = CType(sender, TreeViewItem) If Not IsNothing(tvi) Then _CurrentItem = tvi tvi.InvalidateProperty(IsPossibleDropTargetProperty) End If End SyncLock End Sub End Class </code></pre> <p>End Namespace</p>
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    1. USdansan
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    1. COThanks dansan, it works perfectly! We VB guys are a dying breed and need to stick together!
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      1. USJason Ebersey
 

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