iOS指定视图任意角为圆角

    CGFloat containerViewW = 200;
    CGFloat containerViewH = 200;
    CGFloat containerViewX = (self.view.bounds.size.width - containerViewW) / 2;
    CGFloat containerViewY = (self.view.bounds.size.height - containerViewH) / 2;
    UIView *containerView = [[UIView alloc] initWithFrame:CGRectMake(containerViewX, containerViewY, containerViewW, containerViewH)];
    containerView.backgroundColor = [UIColor blueColor];
    [self.view addSubview:containerView];
    
    /* 指定哪个角为圆角：
                     UIRectCornerTopLeft：左上    
                     UIRectCornerTopRight：右上  
                     UIRectCornerBottomLeft:左下  
                     UIRectCornerBottomRight：右下
     */
    UIRectCorner corners = UIRectCornerTopLeft | UIRectCornerTopRight;
    UIBezierPath *path = [UIBezierPath bezierPathWithRoundedRect:containerView.bounds byRoundingCorners:corners cornerRadii:CGSizeMake(20, 20)];
    CAShapeLayer *shapeLayer = [CAShapeLayer layer];
    shapeLayer.path = path.CGPath;
    
    containerView.layer.mask = shapeLayer;