抓住可怜的行为是不好的做法吗？(Is it a bad practice to catch Throwable?)

 你只能间接做到这一点。 （据我所知） 
 
 
 
 创建一个您的窗体（或控件）大小的位图 
 
 
 创建一个Graphics对象，绘制到该位图（Pixelformat 32bppArgb）'Graphics.FromImage（...） 
 
 
 用透明色清除位图 
 
 
 将所有内容都绘制成该图片 
 
 
 绘制/填充应该排除透明颜色的矩形 
 
 
 将位图绘制到窗体（或控件） 
 
 
 谨防为图形对象使用正确的ComposingMode。 对于绘制到位图使用SourceCopy（否则该区域将不会完全透明）和SourceOver将位图绘制到您的窗体（或控件）。 

You can only do that indirectly. (afaik)
 
 
 
Create a bitmap of the size of your form (or control)
 
 
Create a Graphics object, that draws to that bitmap (Pixelformat 32bppArgb) ' Graphics.FromImage(...)
 
 
Clear the bitmap with transparent color
 
 
Draw everything into that picture
 
 
Draw / Fill the rectangle that should be excluded with transparent color
 
 
Draw the bitmap to your form (or control)
 
 
Beware to use the right ComposingMode for your graphics objects. For drawing to the bitmap use SourceCopy (otherwise the area will not be completely transparent) and SourceOver for drawing the bitmap to your form (or control).