创建 左上角是圆角的视图

- (void)layoutSubviews

{

[super  layoutSubviews];

UIBezierPath*  maskPath = [UIBezierPath bezierPathWithRoundedRect:UIRectCornerTopLeft byRoundingCorners:  cornerRadii:CGSizeMake(5.0,5.0)];

CAShapeLayer*  maskLayer = [CAShapeLayerlayer];

maskLayer.frame=self.bounds;

maskLayer.path= maskPath.CGPath;

self.layer.mask= maskLayer;

}