设置控件的自定义哪边的圆角

UIView *subView = [[UIView alloc] initWithFrame:CGRectMake(100, 100, 100, 100)];
    subView.backgroundColor = [UIColor cyanColor];
    
    // 初始化路径
    /**参数解释
     rect: 控件的frame
     corners: 圆角的点
     UIRectCornerTopLeft     = 1 << 0,
     UIRectCornerTopRight    = 1 << 1,
     UIRectCornerBottomLeft  = 1 << 2,
     UIRectCornerBottomRight = 1 << 3,
     
     cornerRadii: 圆角弧度
     */
    UIBezierPath *path = [UIBezierPath bezierPathWithRoundedRect:subView.bounds byRoundingCorners:UIRectCornerTopLeft | UIRectCornerBottomRight cornerRadii:CGSizeMake(20, 20)];
    
    // 初始化自定义layer
    CAShapeLayer *layer = [[CAShapeLayer alloc] init];
    layer.frame = subView.bounds;
    layer.path = path.CGPath;
    
    // 把自定义的layer赋值给控件
    subView.layer.mask = layer;
    [self.view addSubview:subView];