Process Drag-and-Drop Operations

• Jun 02, 2022
• 3 minutes to read

This topic demonstrates how to customize the GridControl‘s drag-and-drop functionality to support a wide variety of drag-and-drop scenarios.

To Prevent Dragging Specific Records

1. Handle the DataViewBase.StartRecordDrag event.

   Xaml

   <dxg:TreeListView AllowDragDrop="True" StartRecordDrag="OnStartRecordDrag" /> 
   

2. Define records that cannot be dragged.

3. Set the StartRecordDragEventArgs.AllowDrag property to false to prevent records from being dragged.

4. Set the Handled property to true.

   C#

   void OnStartRecordDrag(object sender, StartRecordDragEventArgs e) {
       if (e.Records.Any(x => view.GetNodeByContent(x).HasChildren)) {
           e.AllowDrag = false;
           e.Handled = true;
       }
   } 
   

   VB.NET

   Private Sub OnStartRecordDrag(ByVal sender As Object, ByVal e As StartRecordDragEventArgs)
       If e.Records.Any(Function(x) view.GetNodeByContent(x).HasChildren) Then
           e.AllowDrag = False
           e.Handled = True
       End If
   End Sub
   

   The code sample above allows dragging only leaf nodes.

To Prevent Dropping Items Into Specific Records

1. Handle the DataViewBase.DragRecordOver event.

   XAML

   <dxg:TreeListView AllowDragDrop="True" DragRecordOver="OnDragRecordOver" />
   

2. Define records that reject the data.

3. Set the Effects property to DragDropEffects.None to make the drop target reject the data.

4. Set the Handled property to true.

   C#

   void OnDragRecordOver(object sender, DragRecordOverEventArgs e) {
       string position = ((Employee)e.TargetRecord).Position;
       if (position == "President" || position == "Vice President") {
           e.Effects = DragDropEffects.None;
           e.Handled = true;
       }
   }
   

   VB.NET

   Private Sub OnDragRecordOver(ByVal sender As Object, ByVal e As DragRecordOverEventArgs)
       Dim position As String = (CType(e.TargetRecord, Employee)).Position
   
       If position = "President" OrElse position = "Vice President" Then
           e.Effects = DragDropEffects.None
           e.Handled = True
       End If
   End Sub 
   

To Customize Dragged Items

1. Handle the DataViewBase.DropRecord event.

   XAML

   <dxg:TreeListView AllowDragDrop="True" DropRecord="OnDropRecord" />
   

2. Use the DataObject.GetData method to extract data.

3. Modify extracted data.

   C#

   void OnDropRecord(object sender, DropRecordEventArgs e) {
       object data = e.Data.GetData(typeof(RecordDragDropData));
       foreach (Employee employee in ((RecordDragDropData)data).Records) {
           employee.Position = ((Employee)e.TargetRecord).Position;
           employee.Department = ((Employee)e.TargetRecord).Department;
       }
       if (e.DropPosition == DropPosition.Inside) {
           foreach(Employee employee in ((RecordDragDropData)data).Records) {
               employee.Position = "";
           }
       }
   }
   

   VB.NET

   Private Sub OnDropRecord(ByVal sender As Object, ByVal e As DropRecordEventArgs)
       Dim data As Object = e.Data.GetData(GetType(RecordDragDropData))
   
       For Each employee As Employee In (CType(data, RecordDragDropData)).Records
           employee.Position = (CType(e.TargetRecord, Employee)).Position
           employee.Department = (CType(e.TargetRecord, Employee)).Department
       Next
   
       If e.DropPosition = DropPosition.Inside Then
   
           For Each employee As Employee In (CType(data, RecordDragDropData)).Records
               employee.Position = ""
           Next
       End If
   End Sub
   

   View Example: How to manually control Drag-and-Drop in the GridControl

To Prevent Removing Items After Dropping

1. Handle the DataViewBase.CompleteRecordDragDrop event.

   Xaml

   <dxg:TableView AllowDragDrop="True" CompleteRecordDragDrop="OnCompleteRecordDragDrop" />  
   

2. Set the Handled property to true.

   C#

   void OnCompleteRecordDragDrop(object sender, CompleteRecordDragDropEventArgs e) {
       e.Handled = true;
   } 
   

   VB.NET

   Private Sub OnCompleteRecordDragDrop(ByVal sender As Object, ByVal e As CompleteRecordDragDropEventArgs)
       e.Handled = True
   End Sub
   

To Implement Drag-and-Drop Between Controls and Applications

The GridControl allows dragging records and dropping them in external controls that support drag-and-drop functionality. You can perform drag-and-drop operations within a single application, or between different applications. Refer to the following topics for more information:

• Drag-and-Drop Between GridControl and ListBoxEdit
• Drag-and-Drop Between GridControls
• Drag-and-Drop Between GridControl and Other Controls
• Drag-and-Drop Between Applications