处理圆形图片（如头像）

//    self.profileImageView.layer.cornerRadius = self.profileImageView.width * 0.5;
//    self.profileImageView.layer.masksToBounds = YES;
//使用图层的话，在tableView偶尔会感觉有卡顿的现象

//UIImage+DXDExtension.h 使用分类   使用绘画实现图片圆角
- (UIImage *)circleImage
{
    // NO代表透明
    UIGraphicsBeginImageContextWithOptions(self.size, NO, 0.0);
    
    // 获得上下文
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    
    // 添加一个圆
    CGRect rect = CGRectMake(0, 0, self.size.width, self.size.height);
    CGContextAddEllipseInRect(ctx, rect);
    
    // 裁剪
    CGContextClip(ctx);
    
    // 将图片画上去
    [self drawInRect:rect];
    
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    
    UIGraphicsEndImageContext();
    
    return image;
}

//图片圆角进行封装  使用分类 UIImageView+DXDExtension.h
- (void)setImgWithUrlStr:(NSString *)url
{
    UIImage *placeholder = [[UIImage imageNamed:@"defaultUserIcon"] circleImage];
    [self sd_setImageWithURL:[NSURL URLWithString:url] placeholderImage:placeholder completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, NSURL *imageURL) {
        self.image = image ? [image circleImage] : placeholder;//使用圆角
        //self.image = image ? image : placeholder;//不使用圆角
    }];
}