1.使用layer去裁剪 這兩行代碼在iOS9之前滾動tableview的時候會出現(xiàn)卡頓的顯現(xiàn)，iOS9已經(jīng)修復(fù)了卡頓現(xiàn)象，建議使用第二種方法

    UIImage *image = [UIImage imageNamed:@"avar"];
    UIImageView *imageView = [[UIImageView alloc] initWithImage:image];
    imageView.layer.cornerRadius = image.size.width/2;
    imageView.layer.masksToBounds = YES;```

2.使用上下文裁剪圖片

<pre>        UIGraphicsBeginImageContextWithOptions(image.size, NO, 0);
        //描述裁剪區(qū)域
        UIBezierPath *path = [UIBezierPath bezierPathWithOvalInRect:CGRectMake(0, 0, image.size.width, image.size.height)];
        //設(shè)置裁剪區(qū)域
        [path addClip];
        //畫圖片
        [image drawAtPoint:CGPointZero];
        //取出圖片
        image = UIGraphicsGetImageFromCurrentImageContext();
        //關(guān)閉上下文
        UIGraphicsEndImageContext();
        imageView.image = image;</pre>