这也是一种比较推荐的写法，不会产生离屏渲染问题

- (void)setupCornerRadius
{
    UIBezierPath *maskPath = [UIBezierPath bezierPathWithRoundedRect:CGRectMake(0, 0, KSCREEN_WIDTH, 450)
                                                   byRoundingCorners:UIRectCornerTopLeft | UIRectCornerTopRight
                                                         cornerRadii:CGSizeMake(12, 12)];
    CAShapeLayer *maskLayer = [[CAShapeLayer alloc] init];
    maskLayer.frame = self.contentView.bounds;
    maskLayer.path = maskPath.CGPath;
    self.contentView.layer.mask = maskLayer;
}

效果

上半部分圆角.png