wpf DataGrid 实现拖拽变换位置，双击拖拽向下自动滚动

1. DataGrid_Drop事件是在拖放操作中释放拖动的对象时触发的事件。
2. 使用VisualTreeHelper.HitTest方法获取鼠标释放位置的目标元素。
   循环向上遍历VisualTree，直到找到DataGridRow为止。
   如果找到DataGridRow，则获取其索引。
   检查索引是否有效，如果无效则返回。
   交换CmdButtons列表中的拖拽行与目标行的位置。
3. DragDrop.DoDragDrop方法启动拖动操作

 private void DataGrid_Drop(object sender, DragEventArgs e)
    {
        DataGrid dataGrid = sender as DataGrid;

        int b = dataGrid.SelectedIndex;

        if (dataGrid != null)
        {
            Point position = e.GetPosition(dataGrid);
            HitTestResult hitTestResult = VisualTreeHelper.HitTest(dataGrid, position);
            DependencyObject target = hitTestResult.VisualHit;
            while (target != null && !(target is DataGridRow))
            {
                target = VisualTreeHelper.GetParent(target);
            }
            if (target is DataGridRow)
            {
                DataGridRow row = target as DataGridRow;
                int i = row.GetIndex();

                if (b<0 || i < 0 || b >CmdButtons.Count - 1 || i > CmdButtons.Count - 1)
                {
                    return;
                }

                CmdButton tmp = CmdButtons[b];
                CmdButtons[b] = CmdButtons[i];
                CmdButtons[i] = tmp;
            }
        }
    }



    private void DataGrid_DragOver(object sender, DragEventArgs e)
    {
        if (isPressed)
        {
            ScrollViewer sv = GetScrollViewer(sender as DataGrid);
            var position = e.GetPosition(sv);

            if (position.Y >= 330)
            {
                sv.ScrollToVerticalOffset(sv.VerticalOffset + 15);
            }

            if (position.Y
    <40)
            {
                sv.ScrollToVerticalOffset(sv.VerticalOffset - 15);
            }
        }
    }

    private ScrollViewer GetScrollViewer(DataGrid dataGrid)
    {
        DependencyObject depObject = dataGrid;
        int i = 0;
        while (depObject != null)
        {
            if (depObject is ScrollViewer scrollViewer)
            {
                return scrollViewer;
            }

            depObject = VisualTreeHelper.GetChild(depObject, 0);
        }

        return null;
    }

    private void DataGrid_MouseDoubleClick(object sender, MouseButtonEventArgs e)
    {
        try
        {
            if (e.LeftButton == MouseButtonState.Pressed)
            {
                isPressed = true;
                DragDrop.DoDragDrop(sender as DataGrid, new DataGridRow(), DragDropEffects.Move);
            }

            if (e.LeftButton == MouseButtonState.Released)
            {
                isPressed = false;
            }
        }
        catch (Exception ex)
        {

            throw;
        }
    }