通过贝塞尔曲线

这是给UIView写的类别：
-(void)viewWithCornerRadius:(CGFloat)radius {
UIBezierPath *maskPath = [UIBezierPath bezierPathWithRoundedRect:self.bounds byRoundingCorners:UIRectCornerAllCorners cornerRadii:CGSizeMake(radius, radius)];
CAShapeLayer *maskLayer = [[CAShapeLayer alloc]init];
//设置大小
maskLayer.frame = self.bounds;
//设置图形样子
maskLayer.path = maskPath.CGPath;
self.layer.mask = maskLayer;
}