Cancel Drop

This article demonstrates how to cancel the drop operation. This is useful when you want to forbid the dropping on or the dropping of a particular item when using the RadTreeView control.

To do so, you can subscribe the RadTreeView element to the DragDropManager.Drop event and set the DropAction of the TreeViewDragDropOptions to DropAction.None.

Example 1: Subscribing the control for the Drop event

DragDropManager.AddDropHandler(this.radTreeView, OnDrop, true); 

Example 2: Canceling the drag

private void OnDrop(object sender, Telerik.Windows.DragDrop.DragEventArgs e) 
{ 
    TreeViewDragDropOptions options = DragDropPayloadManager.GetDataFromObject(e.Data, TreeViewDragDropOptions.Key) as TreeViewDragDropOptions; 
    if (options != null && options.DragSourceItem != null) 
    { 
        // cancel the drop operation under a certain condition 
        options.DropAction = DropAction.None; 
    } 
} 

Code Example

This section contains a runnable code example showing how to cancel dropping on a specific item.

Example 3: Treeview definition

<telerik:RadTreeView x:Name="radTreeView" IsDragDropEnabled="True"> 
    <telerik:RadTreeViewItem Header="Sport Categories" IsExpanded="True"> 
        <telerik:RadTreeViewItem Header="Football" IsExpanded="True"> 
            <telerik:RadTreeViewItem Header="Futsal"/> 
            <telerik:RadTreeViewItem Header="Soccer"/> 
        </telerik:RadTreeViewItem> 
        <telerik:RadTreeViewItem Header="Tennis"/> 
        <telerik:RadTreeViewItem Header="Cycling"/> 
    </telerik:RadTreeViewItem> 
</telerik:RadTreeView> 

Example 4: Subscribing the control for DragInitialize

DragDropManager.AddDropHandler(this.radTreeView, OnDrop, true); 

Example 5: Defining the DragInitialize handler and implementing logic that checks if the item can be dragged

private void OnDrop(object sender, Telerik.Windows.DragDrop.DragEventArgs e) 
{ 
    TreeViewDragDropOptions options = DragDropPayloadManager.GetDataFromObject(e.Data, TreeViewDragDropOptions.Key) as TreeViewDragDropOptions; 
    if (options != null && options.DragSourceItem != null) 
    { 
        RadTreeViewItem dropTargetItem = options.DropTargetItem; 
        if (dropTargetItem.Header.ToString() == "Football") 
        { 
            options.DropAction = DropAction.None; 
        } 
    } 
} 
In this case you cannot drop items on the "Football" item.

See Also

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