/* 创建一个Button */
   UIButton * button = [UIButton buttonWithType:(UIButtonTypeSystem)];
   [button setFrame:CGRectMake(100, 100, 100, 100)];
   [self addSubview:button]; 

/* 正厂的圆角需求处理方法 */

  button.layer.cornerRadius = 10.0f; //弧度
  button.layer.masksToBounds = YES;

/* 贝塞尔曲线切割 */
  /**
   *
   * @param UIRectCorner 
   * 左上 UIRectCornerTopLeft   = 1 << 0, 
    左下 UIRectCornerBottomLeft = 1 << 2, 
    右下 UIRectCornerBottomRight = 1 << 3, 
    所有角 UIRectCornerAllCorners = ~0UL
   *
   */
UIBezierPath *maskPath = [UIBezierPath bezierPathWithRoundedRect:button.bounds byRoundingCorners:UIRectCornerTopLeft | UIRectCornerBottomLeft cornerRadii:button.bounds.size];
  CAShapeLayer *maskLayer = [[CAShapeLayer alloc]init];
  //设置大小
  maskLayer.frame = button.bounds;
  //设置图形样子
  maskLayer.path = maskPath.CGPath;
  button.layer.mask = maskLayer;