MVVM Treeview DragDrop Dispatcher处理已暂停，但消息仍在处理中

Question

我有一个应用程序，将从DevExpress网格拖到DevExpress树视图。网格中的DragDropEffects为“复制”并且不移动。用户还可以在TreeView中拖放。我有一个链接到两个控件的MouseMove事件。我必须将其与Grid关联，因为我需要复制对象而不是移动对象。我遇到的问题是，如果我双击一行然后尝试将其拖放，则会收到错误消息“分派器处理已暂停，但消息仍在处理中”。我知道从网格中删除MouseMove事件可以修复该错误，但随后它会移动该项目并且不会将其复制。我希望能够以某种方式告诉XAML中的Grid始终将复制与拖放结合使用。有没有办法解决这个问题？

C＃代码：

  public void MouseMove(object Source, MouseEventArgs E)
    {
        try
        {
            if (E.LeftButton == MouseButtonState.Pressed)
            {
                DragDropEffects ddp = DragDropEffects.Move;
                if (SelectedItem != null)
                {
                    ddp = DragDropEffects.Move;
                }
                else if (SelectedChoice != null)
                {
                    ddp = DragDropEffects.Copy;
                }
                DragDrop.DoDragDrop(E.Source as DependencyObject, SelectedItem == null ? SelectedChoice : SelectedItem, ddp);
            }
        }

        catch (System.InvalidOperationException exo)
        {
            'Dispatcher processing has been suspended, but messages are still being processed.'
        }
        catch (Exception ex)
        {
            MessageBox.Show("Error in MouseMove: " + ex.Message);
        }
    }

XAML：

 <dxg:GridControl x:Name="AvailableChoicesGrid" SelectionMode="Row"  Style="{StaticResource ChoicesGridControl}" ItemsSource="{Binding AvailableChoices}" SelectedItem="{Binding SelectedChoice, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}">
      <i:Interaction.Triggers>
           <i:EventTrigger EventName="MouseMove">
               <ei:CallMethodAction MethodName="MouseMove" TargetObject="{Binding}"/>
           </i:EventTrigger>

           <i:EventTrigger EventName="Drop">
                <ei:CallMethodAction MethodName="DropTarget" TargetObject="{Binding}"/>
           </i:EventTrigger>
      </i:Interaction.Triggers>
      <dxg:GridControl.View>
            <dxg:TableView Style="{StaticResource AvailableChoicesTable}" AllowDragDrop="True" />
      </dxg:GridControl.View>                    
 </dxg:GridControl>