InvalidOperationException: 此 Visual 未连接到 PresentationSource。
StackTrace:
   在 System.Windows.Media.Visual.PointFromScreen(Point point)
   在 GongSolutions.Wpf.DragDrop.DragDrop.<>c.<DoDragSourceMove>b__34_0(Point point)
   在 GongSolutions.Wpf.DragDrop.Utilities.MouseHelper.<>c__DisplayClass1_0.<HookMouseMove>b__0(Object _, EventArgs _)
   在 System.Windows.Threading.DispatcherTimer.FireTick(Object unused)
   在 System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   在 System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)