WPF OnRender Z 顺序控制？

Question

我有一个自定义面板，它实现了其子项的良好自定义布局。我想向面板添加一些额外的图形，因此覆盖 OnRender 以添加额外的矩形等。它工作得很好，除了 OnRender 似乎只添加到背景。有没有办法让 OnRender 绘图位于子项之上？

示例面板...

public class RenderPanel : WrapPanel
{
    protected override void OnRender(DrawingContext drawingContext)
    {
        base.OnRender(drawingContext);
        drawingContext.DrawRectangle(Brushes.Red, 
                                     new Pen(Brushes.Black, 2), 
                                     new Rect(0, 0, 100, 100));
    }
}

...这样使用...

<Grid>
    <my:RenderPanel HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
        <Button Margin="10" Content="Hello"/>
        <Button Margin="10" Content="Hello"/>
        <Button Margin="10" Content="Hello"/>
        <Button Margin="10" Content="Hello"/>
    </my:RenderPanel>
</Grid>

Answer 1

我会让你的“RenderPanel”继承自canvas，然后将其放置在WrapPanel 之上并根据需要指定ZIndex。像这样的东西应该有效:

<Grid>
    <WrapPanel HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Canvas.ZIndex="0">
        <Button Margin="10" Content="Hello"/>
        <Button Margin="10" Content="Hello"/>
        <Button Margin="10" Content="Hello"/>
        <Button Margin="10" Content="Hello"/>
    </WrapPanel>
    <my:RenderPanel HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Canvas.ZIndex="1" />
</Grid>