关于CALayer导致的crash问题

在使用层来手动绘制视图时，如果有添加子层，并且希望使用使用

-(void) drawLayer: (CALayer*) layer inContext: (CGContextRef) context

来自己用代码绘制视图时，注意不要设置其delegate为uiview类型实例。会导致程序crash。

关于这一点，苹果官方在文档中已有说明。解决办法：

he lightest-wight solution would be to create a small helper class in the the file as the UIView that's using the CALayer:

In MyView.h

@interface MyLayerDelegate : NSObject . . . @end 

In MyView.m

@implementation MyLayerDelegate - (void)drawLayer:(CALayer*)layer inContext:(CGContextRef)ctx { . . . } @end 

Just place those at the top of your file, immediately below the #import directives. That way it feels more like using a "private class" to handle the drawing (although it isn't -- the delegate class can be instantiated by any code that imports the header).