UIImageView * imageView = [[UIImageView alloc] initWithFrame:CGRectMake(100, 300, 100, 100)];
imageView.image = [UIImage imageNamed:@"屏幕快照 2016-01-06 17.44.20"];
[self.view addSubview:imageView];
UIBezierPath * maskPath = [UIBezierPath bezierPathWithRoundedRect:imageView.bounds byRoundingCorners:UIRectCornerBottomLeft|UIRectCornerTopLeft cornerRadii:CGSizeMake(20, 20)];
CAShapeLayer * maskLayer = [[CAShapeLayer alloc]init];
maskLayer.frame = imageView.bounds;
maskLayer.path = maskPath.CGPath;
imageView.layer.mask = maskLayer;
