objective-c - iOS 解析不同 json 字符串的正确条件

Question

我正在为用户身份验证系统解析 json。

如果登录成功，服务器发送以下用户对象；

{

    "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."

]

我应该使用什么 if() 语句来解析和显示两种情况下的响应？

Answer 1

//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 {

}