设置圆角 但未必四个都是圆角

[self setMaskTo:yourView byRoundingCorners:UIRectCornerTopLeft|UIRectCornerTopRight];

- (void)setMaskTo:(UIView*)view byRoundingCorners:(UIRectCorner)corners
{
    UIBezierPath *rounded = [UIBezierPath bezierPathWithRoundedRect:view.bounds
                                                  byRoundingCorners:corners
                                                        cornerRadii:CGSizeMake(8.0, 8.0)];
    CAShapeLayer *shape = [[CAShapeLayer alloc] init];
    [shape setPath:rounded.CGPath];    
    view.layer.mask = shape;
}