图片异步下载

@property (weak, nonatomic) IBOutlet UIImageView *photo;

========

    //1.准备URL

    NSURL *url = [[NSURL alloc]initWithString:IMG_ASYN];

    

    //2.准备请求对象

    NSURLRequest *request = [[NSURLRequest alloc]initWithURL:url];

    

    //3.异步链接下载

    [NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {

        //获取图片

        UIImage *image = [UIImage imageWithData:data];

        

        //设置图片

        [_photo setImage:image];

        

        

    }];