最近遇到这个需求，以为是多难的事。
结果就两三行搞定。
#import <QuartzCore/QuartzCore.h>
//UIView or inherited from uiview.
self.layer.maksToBounds = YES;
self.layer.cornerRadius = 5.0; //根据需要调整
////官方的切圆角代码：
static void addRoundedRectToPath( CGContextRef context , CGRect rect ,
float ovalWidth,float ovalHeight)
{
float fw, fh;
if ( ovalWidth == 0 || ovalHeight == 0 ) { // 1
CGContextAddRect( context , rect ) ;
return ;
}
CGContextSaveGState( context ) ; // 2
CGContextTranslateCTM ( context , CGRectGetMinX( rect ) , // 3
CGRectGetMinY( rect ) ) ;
CGContextScaleCTM ( context , ovalWidth, ovalHeight) ; // 4
fw = CGRectGetWidth ( rect ) / ovalWidth; // 5
fh = CGRectGetHeight ( rect ) / ovalHeight; // 6
CGContextMoveToPoint( context , fw, fh/ 2 ) ; // 7
CGContextAddArcToPoint( context , fw, fh, fw/ 2 , fh, 1 ) ; // 8
CGContextAddArcToPoint( context , 0 , fh, 0 , fh/ 2 , 1 ) ; // 9
CGContextAddArcToPoint( context , 0 , 0 , fw/ 2 , 0 , 1 ) ; // 10
CGContextAddArcToPoint( context , fw, 0 , fw, fh/ 2 , 1 ) ; // 11
CGContextClosePath( context ) ; // 12
CGContextRestoreGState( context ) ; // 13
}