WPF: 旋轉Thumb後，DragDelta移動距離出錯的解決

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當Thumb跟隨Grid旋轉90度後，拖拽控制項時會飛掉。

<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);        }

 

 

這是由於座標系不統一造成的。Canvas.SeltLeft 和 Canvas.SetTop是用的Canvas座標系。而Thumb的e.HorizontalChange 和 e.VerticalChange 是根據滑鼠相對於Thumb自身座標系計算出來的， 兩個座標系有個90度的角度差。將e.HorizontalChange 和 e.VerticalChange轉換到Canvas的座標系下，拖拽就沒問題了。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);        }