1.请求json数据，使用AFHTTPRequestOperation完成

    NSString *str=[NSString stringWithFormat:@"http://int.dpool.sina.com.cn/iplookup/iplookup.php?format=json&ip=218.4.255.255"];
     
    NSURL *url = [NSURL URLWithString:[str stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]];                        // UTF－8
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc]initWithRequest:request];
    // 请求数据，设置成功与失败的回调函数
    [operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
        NSString *html = operation.responseString;
        NSData* data=[html dataUsingEncoding:NSUTF8StringEncoding];
        id dict=[NSJSONSerialization  JSONObjectWithData:data options:0 error:nil];
        NSLog(@"获取到的数据为：%@",dict);
    }failure:^(AFHTTPRequestOperation *operation, NSError *error) {
        NSLog(@"发生错误！%@",error);
    }];
    // 加入队列
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    [queue addOperation:operation];