UIButton,设置为UIButtonTypeCustom类型时，做圆角效果

 Add QuartzCore.framework to your project and this line to your .m file. 
      #import <QuartzCore/QuartzCore.h> 

示例代码如下： 
     

1. UIButton *moreButton = [UIButton buttonWithType:UIButtonTypeCustom];  
2.       moreButton.frame = CGRectMake(1.0f, 1.0f, cell.contentView.frame.size.width-2, cell.contentView.frame.size.height-2);  
3.       [moreButton.layer setMasksToBounds:YES];  
4.       [moreButton.layer setCornerRadius:10.0]; //设置矩形四个圆角半径  
5.       [moreButton.layer setBorderWidth:1.0]; //边框宽度  
6.       moreButton.backgroundColor = [UIColor clearColor];  

原文地址：http://stackoverflow.com/questions/7813379/what-does-receiver-type-calayer-for-instance-message-is-a-forward-declaration