static NSString * baseUrl = @"http://192.168.1.123/images/";

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
   
    SXTShopCell * cell = [tableView dequeueReusableCellWithIdentifier:identifier];
   
    SXTShop * shop = self.dataList[indexPath.row];
   
    cell.shop = shop;
   
    //为了避免重复加载的问题，创建了downloadImage，downloadImage属于数据源，当tableview滚动的时候就可以给cell的数据赋值
   
    if (shop.downloadImage) {
       
        //如果下载过，直接从内存中获取图片
        cell.iconView.image = shop.downloadImage;
       
    } else {
      
        //设置默认图片
        cell.iconView.image = [UIImage imageNamed:@"defaultImage"];
       
        //如果未下载过,开启异步线程
        NSBlockOperation * op = [NSBlockOperation blockOperationWithBlock:^{
           
            //模拟网络延时
            [NSThread sleepForTimeInterval:1];
           
            //通过url获取网络数据
            NSData * data = [NSData dataWithContentsOfURL:[NSURL URLWithString:[NSString stringWithFormat:@"%@%@",baseUrl,shop.shop_image]]];
           
            //将数据装换为图片
            UIImage * image = [UIImage imageWithData:data];
           
            //如果有图片
            if (image) {
               
                //通知model，将图片赋值给downloadImage，以便下次从内存获取
                shop.downloadImage = image;

//获取主队列，更新UI
                [[NSOperationQueue mainQueue] addOperationWithBlock:^{
                   
                    //刷新第indexPath单元的表格
                    [self.tableView reloadRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
               
                }];
            }
        }];
        //将请求加入全局队列
        [self.queue addOperation:op];
       
    }

return cell;
}