UIBezierPath *maskPath =[UIBezierPathbezierPathWithRoundedRect:button.boundsbyRoundingCorners:UIRectCornerTopLeft|UIRectCornerTopRightcornerRadii:CGSizeMake(4.0,4.0)];

CAShapeLayer *maskLayer =[ [CAShapeLayer alloc]init];

maskLayer.frame = button.bounds;

maskLayer.path = maskPath.CGPath;

button.layer.mask = maskLayer;

以上是将button的左上和右上的边角设置为半径4.0的圆角

UIRectCorneryou4种属性:

UIRectCornerTopLeft;左上

UIRectCornerTopRight;右上

UIRectCornerBottomLeft;左下

UIRectCornerBottomRight;右下

UIRectCornerAllCorners;4个边角