在WPF窗体中重绘

写这篇主要是为了验证任何元素自身都具备绘图功能.

在默认Window中重写OnRender方法

protected override void OnRender(DrawingContext drawingContext)
{
    drawingContext.DrawRectangle(Brushes.White, null, new Rect(0, 0, this.ActualWidth, ActualHeight));

    drawingContext.DrawRectangle(Brushes.Blue, null, new Rect(0, 0, 300, 300));
    drawingContext.DrawRectangle(Brushes.Green, null, new Rect(0, 0, 200, 200));
    drawingContext.DrawRectangle(Brushes.Red, null, new Rect(0, 0, 100, 100));


    base.OnRender(drawingContext);
}

结果还是空白一片.
窗体的默认视觉树

解决方法1:去掉默认视觉树

protected override Visual GetVisualChild(int index)
{
    return null;
}

结果恢复正常

但此方法破坏了窗体默认视觉树,影响了其内部功能

解决方法2:将默认北京颜色设置为空

this.Background = null;

搞了半天原来是被遮住了

记录一下技巧