¿Cómo analizo JSON con Objective-C?

Soy nuevo en el iPhone. ¿Alguien puede decirme los pasos a seguir para analizar estos datos y obtener los detalles de la actividad, el nombre y el apellido?

{
    "#error": false, 
    "#data": {
        "": {
            "activity_id": "35336", 
            "user_id": "1", 
            "user_first_name": "Chandra Bhusan", 
            "user_last_name": "Pandey", 
            "time": "1300870420", 
            "activity_details": "Good\n", 
            "activity_type": "status_update", 
            "photo_url": "http://184.73.155.44/hcl-meme/QA_TEST/sites/default/files/pictures/picture-1627435117.jpg"
        }, 
        "boolean": "1", 
        "1": {
            "1": {
                "photo_1_id": "9755"
            }, 
            "activity_id": "35294", 
            "album_name": "Kalai_new_Gallery", 
            "user_id": "31", 
            "album_id": "9754", 
            "user_first_name": "Kalaiyarasan", 
            "user_last_name": "Balu", 
            "0": {
                "photo_0_id": "9756"
            }, 
            "time": "1300365758", 
            "activity_type": "photo_upload", 
            "photo_url": "http://184.73.155.44/hcl-meme/QA_TEST/"
        }, 
        "3": {
            "activity_id": "35289", 
            "user_id": "33", 
            "user_first_name": "Girija", 
            "user_last_name": "S", 
            "time": "1300279636", 
            "activity_details": "girija Again\n", 
            "activity_type": "status_update", 
            "photo_url": "http://184.73.155.44/hcl-meme/QA_TEST/sites/default/files/pictures/picture-33-6361851323080768.jpg"
        }, 
        "2": {
            "owner_first_name": "Girija", 
            "activity_id": "35290", 
            "activity_details": "a:2:{s:4:\"html\";s:51:\"!user_fullname and !friend_fullname are now friends\";s:4:\"type\";s:10:\"friend_add\";}", 
            "activity_type": "friend accept", 
            "owner_last_name": "S", 
            "time": "1300280400", 
            "photo_url": "http://184.73.155.44/hcl-meme/QA_TEST/sites/default/files/pictures/picture-33-6361851323080768.jpg", 
            "owner_id": "33"
        }, 
        "4": {
            "activity_id": "35288", 
            "user_id": "33", 
            "user_first_name": "Girija", 
            "user_last_name": "S", 
            "time": "1300279530", 
            "activity_details": "girija from mobile\n", 
            "activity_type": "status_update", 
            "photo_url": "http://184.73.155.44/hcl-meme/QA_TEST/sites/default/files/pictures/picture-33-6361851323080768.jpg"
        }
    }
}

Con la perspectiva de los lanzamientos de OS X v10.7 e iOS 5, probablemente lo primero que se recomiende ahora es NSJSONSerializationel analizador JSON proporcionado por Apple. Use las opciones de terceros solo como respaldo si encuentra que esa clase no está disponible en tiempo de ejecución.

Así por ejemplo:

NSData *returnedData = ...JSON data, probably from a web request...

// probably check here that returnedData isn't nil; attempting
// NSJSONSerialization with nil data raises an exception, and who
// knows how your third-party library intends to react?

if(NSClassFromString(@"NSJSONSerialization"))
{
    NSError *error = nil;
    id object = [NSJSONSerialization
                      JSONObjectWithData:returnedData
                      options:0
                      error:&error];

    if(error) { /* JSON was malformed, act appropriately here */ }

    // the originating poster wants to deal with dictionaries;
    // assuming you do too then something like this is the first
    // validation step:
    if([object isKindOfClass:[NSDictionary class]])
    {
        NSDictionary *results = object;
        /* proceed with results as you like; the assignment to
        an explicit NSDictionary * is artificial step to get 
        compile-time checking from here on down (and better autocompletion
        when editing). You could have just made object an NSDictionary *
        in the first place but stylistically you might prefer to keep
        the question of type open until it's confirmed */
    }
    else
    {
        /* there's no guarantee that the outermost object in a JSON
        packet will be a dictionary; if we get here then it wasn't,
        so 'object' shouldn't be treated as an NSDictionary; probably
        you need to report a suitable error condition */
    }
}
else
{
    // the user is using iOS 4; we'll need to use a third-party solution.
    // If you don't intend to support iOS 4 then get rid of this entire
    // conditional and just jump straight to
    // NSError *error = nil;
    // [NSJSONSerialization JSONObjectWithData:...
}

No reinventes la rueda. Utilice json-framework o algo similar.

Si decide usar json-framework, así es como analizaría una cadena JSON en un NSDictionary:

SBJsonParser* parser = [[[SBJsonParser alloc] init] autorelease];
// assuming jsonString is your JSON string...
NSDictionary* myDict = [parser objectWithString:jsonString];

// now you can grab data out of the dictionary using objectForKey or another dictionary method

NSString* path  = [[NSBundle mainBundle] pathForResource:@"index" ofType:@"json"];

//将文件内容读取到字符串中，注意编码NSUTF8StringEncoding 防止乱码，
NSString* jsonString = [[NSString alloc] initWithContentsOfFile:path encoding:NSUTF8StringEncoding error:nil];

//将字符串写到缓冲区。
NSData* jsonData = [jsonString dataUsingEncoding:NSUTF8StringEncoding];

NSError *jsonError;
id allKeys = [NSJSONSerialization JSONObjectWithData:jsonData options:NSJSONWritingPrettyPrinted error:&jsonError];


for (int i=0; i<[allKeys count]; i++) {
    NSDictionary *arrayResult = [allKeys objectAtIndex:i];
    NSLog(@"name=%@",[arrayResult objectForKey:@"storyboardName"]);

}

expediente:

 [
  {
  "ID":1,
  "idSort" : 0,
  "deleted":0,
  "storyboardName" : "MLMember",
  "dispalyTitle" : "76.360779",
  "rightLevel" : "10.010490",
  "showTabBar" : 1,
  "openWeb" : 0,
  "webUrl":""
  },
  {
  "ID":1,
  "idSort" : 0,
  "deleted":0,
  "storyboardName" : "0.00",
  "dispalyTitle" : "76.360779",
  "rightLevel" : "10.010490",
  "showTabBar" : 1,
  "openWeb" : 0,
  "webUrl":""
  }
  ]

Análisis JSON mediante NSJSONSerialization

   NSString* path  = [[NSBundle mainBundle] pathForResource:@"data" ofType:@"json"];
   
    //Here you can take JSON string from your URL ,I am using json file
    NSString* jsonString = [[NSString alloc] initWithContentsOfFile:path encoding:NSUTF8StringEncoding error:nil];
    NSData* jsonData = [jsonString dataUsingEncoding:NSUTF8StringEncoding];
    NSError *jsonError;
    NSArray *jsonDataArray = [NSJSONSerialization JSONObjectWithData:[jsonString dataUsingEncoding:NSUTF8StringEncoding] options:kNilOptions error:&jsonError];
  
    NSLog(@"jsonDataArray: %@",jsonDataArray);

    NSDictionary *jsonObject = [NSJSONSerialization JSONObjectWithData:jsonData options:kNilOptions error:&jsonError];
if(jsonObject !=nil){
   // NSString *errorCode=[NSMutableString stringWithFormat:@"%@",[jsonObject objectForKey:@"response"]];
   
        
        if(![[jsonObject objectForKey:@"#data"] isEqual:@""]){
            
            NSMutableArray *array=[jsonObject objectForKey:@"#data"];
             // NSLog(@"array: %@",array);
            NSLog(@"array: %d",array.count);  
            
            int k = 0;
            for(int z = 0; z<array.count;z++){
                
                NSString *strfd = [NSString stringWithFormat:@"%d",k];
                NSDictionary *dicr = jsonObject[@"#data"][strfd];
                k=k+1;
                // NSLog(@"dicr: %@",dicr);
                 NSLog(@"Firstname - Lastname   : %@ - %@",
                     [NSMutableString stringWithFormat:@"%@",[dicr objectForKey:@"user_first_name"]],
                     [NSMutableString stringWithFormat:@"%@",[dicr objectForKey:@"user_last_name"]]);
            }
            
          }

     }

Puede ver la salida de la consola como se muestra a continuación:

Nombre - Apellido: Chandra Bhusan - Pandey

Nombre - Apellido: Kalaiyarasan - Balu

Nombre - Apellido: (nulo) - (nulo)

Nombre - Apellido: Girija - S

Nombre - Apellido: Girija - S

Nombre - Apellido: (nulo) - (nulo)

1. Recomiendo y uso TouchJSON para analizar JSON.

2. Para responder a tu comentario a Alex. Aquí hay un código rápido que debería permitirle obtener los campos como activity_details, last_name, etc. del diccionario json que se devuelve:

   NSDictionary *userinfo=[jsondic valueforKey:@"#data"];
   NSDictionary *user;
   NSInteger i = 0;
   NSString *skey;
   if(userinfo != nil){
       for( i = 0; i < [userinfo count]; i++ ) {
           if(i)
               skey = [NSString stringWithFormat:@"%d",i];
           else
               skey = @"";
   
           user = [userinfo objectForKey:skey];
           NSLog(@"activity_details:%@",[user objectForKey:@"activity_details"]);
           NSLog(@"last_name:%@",[user objectForKey:@"last_name"]);
           NSLog(@"first_name:%@",[user objectForKey:@"first_name"]);
           NSLog(@"photo_url:%@",[user objectForKey:@"photo_url"]);
       }
   }