WPF: 旋转Thumb后，DragDelta移动距离出错的解决

当Thumb跟随Grid旋转90度后，拖拽控件时会飞掉。

<Grid x:Name="gridMain" Width="100" Height="50" Background="Green" RenderTransformOrigin="0.5,0.5" Canvas.Left="100" Canvas.Top="100">
                <Grid.RenderTransform>
                    <RotateTransform x:Name="rotate" Angle="90"></RotateTransform>
                </Grid.RenderTransform>
                <Thumb x:Name="thumbMain" Opacity="0.8" DragDelta="Thumb_DragDelta"></Thumb>
            </Grid>

private void Thumb_DragDelta(object sender, System.Windows.Controls.Primitives.DragDeltaEventArgs e)
        {
            Canvas.SetLeft(gridMain, Canvas.GetLeft(gridMain) + e.HorizontalChange);
            Canvas.SetTop(gridMain, Canvas.GetTop(gridMain) + e.VerticalChange);
        }

 

 

这是由于坐标系不统一造成的。Canvas.SeltLeft 和 Canvas.SetTop是用的Canvas坐标系。而Thumb的e.HorizontalChange 和 e.VerticalChange 是根据鼠标相对于Thumb自身坐标系计算出来的， 两个坐标系有个90度的角度差。将e.HorizontalChange 和 e.VerticalChange转换到Canvas的坐标系下，拖拽就没问题了。如下：

private void Thumb_DragDelta(object sender, System.Windows.Controls.Primitives.DragDeltaEventArgs e)
        {
            Point ptChange = rotate.Transform(new Point(e.HorizontalChange, e.VerticalChange));
            Canvas.SetLeft(gridMain, Canvas.GetLeft(gridMain) + ptChange.X);
            Canvas.SetTop(gridMain, Canvas.GetTop(gridMain) + ptChange.Y);
        }