我刚刚处理了这个问题。不要在 CGLayer 上绘制背景，然后将 UIView 的背景设置为：

I just dealt with this. Don't draw a background on the CGLayer and then set the background of the UIView to:

self.backgroundColor = [UIColor clearColor];

应该这样做，您的png将具有透明背景。

That should do it and your png will have a transparent background.