圆角设置可以指定左上、左下、右上、右下角；单个指定或多个指定。

///设置圆角[左上、右上角]

- (void)setCircular{

    UIBezierPath *maskPath = [UIBezierPath bezierPathWithRoundedRect:self.bounds byRoundingCorners:UIRectCornerTopLeft | UIRectCornerTopRight cornerRadii:CGSizeMake(20,20)];

    //创建 layer

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

    maskLayer.frame = self.bounds;

    //赋值

    maskLayer.path = maskPath.CGPath;

    self.layer.mask = maskLayer;

}