使用AFJSONRequestOperation

Question

我正在尝试从服务于JSON的web服务中获取一些数据。但我不知道我的代码出了什么问题。看上去很简单，但我找不到任何数据。

这是密码：

NSURLRequest *request = [NSURLRequest requestWithURL:URL];

AFJSONRequestOperation *operation = [AFJSONRequestOperation
   JSONRequestOperationWithRequest:request 
   success:^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON) {
     DumpDic = (NSDictionary*)[JSON valueForKeyPath:@"description"] ;
   } 
   failure:nil
];

[operation start];

AboutTXT = [DumpDic objectForKey:@"description"];

这是JSON URL。

编辑

来自URL的JSON：

{
   "clazz":"AboutList",
   "description":{
      "clazz":"DescriptionContent",
      "description":"ASTRO Holdings Sdn. Bhd. (AHSB) Group operates through two holding companies – ASTRO Overseas Limited (AOL) which owns the portfolio of regional investments and ASTRO Malaysia Holdings Sdn Bhd (AMH / ASTRO) for the Malaysian business, which was privatized in 2010 and is currently owned by Usaha Tegas Sdn Bhd/its affiliates, and Khazanah Nasional Berhad."
   },
   "id":{
      "inc":-1096690569,
      "machine":1178249826,
      "new":false,
      "time":1339660115000,
      "timeSecond":1339660115
   },
   "refKey":"AboutList"
}

Answer 1

它是否成功地连接到服务器，是否正在调用成功块？

填写failure块并NSLog由failure块返回的NSError：

failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error, id JSON) {
                                                        NSLog(@"%@", [error userInfo]);
                                                    }

我还有另外一个技巧，我建议用AFNetwork的AFHTTPClient构建AFHTTPClient，它可以帮助处理各种事情，并且通常会使事情变得更简单。您可以设置基本URL，然后给它一个附加到该基的路径。就像这样：

AFHTTPClient *httpClient = [[AFHTTPClient alloc] initWithBaseURL:address];
[httpClient setParameterEncoding:AFJSONParameterEncoding];
NSMutableURLRequest *jsonRequest = [httpClient requestWithMethod:@"POST"
                                                            path:@"events"
                                                      parameters:dict];

另外，我建议您不要使用valueForKeyPath，只需执行objectForKey：

[JSON objectForKey:@"description"];

此外，您不应该在那里访问DumpDic：

[operation start];
AboutTXT = [DumpDic objectForKey:@"description"];

这是一个异步调用，因此一旦操作开始，DumpDic很可能会在从服务器分配数据之前被访问。因此，您正在访问一个可能还不存在的密钥。

这应该在成功或失败块中完成。一旦连接完成并准备使用这些数据，就会调用这些块。

所以它应该看起来更像这样：

AFJSONRequestOperation *operation =
  [AFJSONRequestOperation JSONRequestOperationWithRequest:request
                                                  success:^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON) {
    DumpDic = [JSON objectFor:@"description"];
    AboutTXT = [DumpDic objectForKey:@"description"];
  }
  failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error, id JSON) {
    NSLog(@"%@", [error userInfo]);
  }];

[operation start];