c# - WPF C#拖放传递起点的值

Question

我在这里有这段代码：

       public void DragSource_PreviewMouseMove(object sender, MouseEventArgs e)
    {
        // Get the current mouse position
        Point mousePos = e.GetPosition(null);

        Vector diff = startPoint - mousePos; // startPoint error

        if (e.LeftButton == MouseButtonState.Pressed &&
            Math.Abs(diff.X) > SystemParameters.MinimumHorizontalDragDistance ||
            Math.Abs(diff.Y) > SystemParameters.MinimumVerticalDragDistance)
        {
            Label lbl = (Label)sender;
            DataObject dataObj = new DataObject(lbl.Content);
            DragDrop.DoDragDrop(lbl, dataObj, DragDropEffects.All);
        } 
    }

    public void DragSource_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    {
       var startPoint = e.GetPosition(null);
    }

它说 startPoint 在 previewmousemove 中不存在，我在 WPF 中执行此操作，通常我将其保存到会话中并将其传递但 WPF 没有会话，我该如何解决此错误？我正在学习如何从http://wpftutorial.net/DragAndDrop.html和http://blogs.msdn.com/b/jaimer/archive/2007/07/12/drag-drop-in-进行拖放wpf-explained-end-to-end.aspx

Answer 1

您可以挂断 PreviewMouseLeftButtonDown 事件并将 GetPosition 结果存储在类的私有变量起点中。

private Point _startPoint;
yourTreeview_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
    _startPoint = e.GetPosition(null);
}