Objective c 解析不同json字符串的正确条件

我正在为用户身份验证系统解析json

如果登录成功，服务器将发送以下用户对象

{

    "users": {
        "id": "1",
        "FB_first_name": null,
        "FB_last_name": null,
        "FB_gender": null,
        "FB_id": null,
        "FB_link": null,
        "FB_locale": null,
        "FB_name": null,
        "FB_username": null,
        "created_at": "2011-01-02 08:30:59 UTC",
        "updated_at": "2011-01-02 08:31:23 UTC",
        "email": "admin@8repz.com",
        "language_id": "1"
    }

}

我使用以下代码对其进行解析

    NSDictionary *userDic = (NSDictionary*)[(NSDictionary*)results objectForKey:@"users"];

    User *aUser = [[User alloc] initWithID:[userDic objectForKey:@"id"]
                              withUserName:[userDic objectForKey:@"FB_name"]
                             withUserEmail:[userDic objectForKey:@"email"]
                             withUserFName:[userDic objectForKey:@"FB_first_name"]];

但如果用户无效，服务器会发送以下响应：

[

    "Invalid Email or Password."

]

---

在这两种情况下，我应该使用什么

if（）

语句来解析和显示响应？

你知道这是一个无效的json，对吗？我在发帖之前验证了它。json的根可以是字典或数组。你知道这是一个无效的json，是吗？我在发帖前验证了它。JSON的根可以是字典或数组。我喜欢这个结果。这比我使用嵌套if语句的方法更简洁。我喜欢这个结果。它比我使用嵌套if语句的方法更简洁。

//IF RESPONSE IS SIMPLY A STRING OBJECT FOR INVALID STRING, YOU HAVE BAD DATA
if(![results isEqualToString:@"Invalid Email or Password."]){
     if([results objectForKey:@"users"]){  //Check to ensure users object exists
          //You're good 
           NSDictionary *userDic = (NSDictionary*)[(NSDictionary*)results objectForKey:@"users"];

            User *aUser = [[User alloc] initWithID:[userDic objectForKey:@"id"]
                              withUserName:[userDic objectForKey:@"FB_name"]
                             withUserEmail:[userDic objectForKey:@"email"]
                             withUserFName:[userDic objectForKey:@"FB_first_name"]];
     }
}else{
     //Handle error
}

//parse out the json data
NSError* error;
id json = [NSJSONSerialization JSONObjectWithData:responseData options:NSJSONReadingMutableContainers error:&error];
if ([json isKindOfClass:[NSArray class]){
    //You have to be sure that on error it returns array not a dictionary
    NSArray *arr = (NSArray*)json;
    NSString *errorMsg = [arr objectAtIndex:0];
}
else {

}