iOS 设置按钮圆角(4个角都可随意设置)

设置按钮的4个角：
左上：UIRectCornerTopLeft
左下：UIRectCornerBottomLeft
右上：UIRectCornerTopRight
右下：UIRectCornerBottomRight

例子代码：

UIButton *button = [[UIButton alloc] initWithFrame:CGRectMake(50, 60, 80, 40)];
button.backgroundColor = [UIColor orangeColor];
[self.view addSubview:button];
 
//这里设置的是左上和左下角
UIBezierPath *maskPath = [UIBezierPath bezierPathWithRoundedRect:button.bounds   byRoundingCorners:UIRectCornerBottomLeft |    UIRectCornerTopLeft    cornerRadii:CGSizeMake(8, 8)];
CAShapeLayer *maskLayer = [[CAShapeLayer alloc] init];
maskLayer.frame = button.bounds;
maskLayer.path = maskPath.CGPath;
button.layer.mask = maskLayer;

效果图：