imageview属性

//允许手势、点击、动画

imageView.userInteractionEnabled = YES;

设置UIImageView的contentMode为UIViewContentModeScaleAspectFit. 再设置图片后，就不会扭曲图片，而是等比例缩放 
属性contentMode：
http://www.2cto.com/kf/201507/412894.html




UIImageView添加圆角

最直接的方法就是使用如下属性设置
imgView.layer.cornerRadius = 10;
// 这一行代码是很消耗性能的
imgView.clipsToBounds = YES;

**这是离屏渲染（off-screen-rendering），消耗性能的**

给UIImage添加生成圆角图片的扩展API：这是on-screen-rendering
- (UIImage *)imageWithCornerRadius:(CGFloat)radius {
CGRect rect = (CGRect){0.f, 0.f, self.size};
 
UIGraphicsBeginImageContextWithOptions(self.size, NO, UIScreen.mainScreen.scale);
CGContextAddPath(UIGraphicsGetCurrentContext(),
 [UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:radius].CGPath);
CGContextClip(UIGraphicsGetCurrentContext());
 
[self drawInRect:rect];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
 
UIGraphicsEndImageContext();
 
return image;
}