JSON ObjectiveC - Error

Question

Receiving the following error. I believe it has to do with the NSDictionary in the results of JSON array. I.e. NSDictionary within an NSDictionary maybe?

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFString objectForKey:]: unrecognized selector sent to instance 0x7f9298554560'

This is the JSON service when called. This is printed directly out of XCode but it looks clean to me.

    Printing description of self->metArray:
{
    weatherObservation =     {
        ICAO = YBBN;
        clouds = "few clouds";
        cloudsCode = FEW;
        countryCode = AU;
        datetime = "2014-11-24 03:00:00";
        dewPoint = 20;
        elevation = 5;
        hectoPascAltimeter = 1014;
        humidity = 61;
        lat = "-27.38333333333333";
        lng = "153.1333333333333";
        observation = "YBBN 240300Z 02019KT 9999 FEW029 SCT250 28/20 Q1014";
        stationName = "Brisbane Airport M. O";
        temperature = 28;
        weatherCondition = "n/a";
        windDirection = 20;
        windSpeed = 19;
    };
}

This is the code that invokes the JSON service.

 -(void)getMetar{

   // NSString *location = @"YBBN";
    NSString * const metarUrl =@"http://api.geonames.org/weatherIcaoJSON?ICAO=YBBN&username=demo";

    NSURL *url2 = [NSURL URLWithString:metarUrl];
    NSData *data2 = [NSData dataWithContentsOfURL:url2];

    metArray = [NSJSONSerialization JSONObjectWithData:data2 options:kNilOptions error:nil];

    //Create an NSDictionary for the weather data to be stored.
    NSDictionary *metarJson = [NSJSONSerialization JSONObjectWithData:data2 options:kNilOptions error:nil];

    //Loop through the JSON array
    NSArray *currentMetarArray = metarJson[@"weatherObservation"];

    //set up array and json call
    metarArray = [[NSMutableArray alloc]init];
   for (NSDictionary *metaritem in currentMetarArray)
    {
        //create our object
        NSString *nClouds = [metaritem objectForKey:@"clouds"];
        NSString *nObservation = [metaritem objectForKey:@"observation"];

        //Add the object to our animal array
        [metarArray addObject:[[metar alloc]initWithclouds:(nClouds) andobservation:nObservation]];

    }
}

It looks okay to me but maybe that is because I have been looking at it for hours.

Any ideas?

Answer 1

I go to your URL and get this message {"status":{"message":"the daily limit of 30000 credits for demo has been exceeded. Please use an application specific account. Do not use the demo account for your application.","value":18}}

But you can try my code, it worked for me

NSString *strUrl = @"http://api.geonames.org/weatherIcaoJSON?ICAO=YBBN&username=demo";
NSURL *url = [NSURL URLWithString:strUrl];
NSData *data = [NSData dataWithContentsOfURL:url];

NSError *error;

NSDictionary *json = [NSJSONSerialization JSONObjectWithData:data options:0 error:&error];

NSDictionary *weatherObservation = [json objectForKey:@"status"];

for (id key in weatherObservation) {
    id value = [weatherObservation objectForKey:key];

    NSLog(@"key = %@, value = %@", key, value);
}

Answer 2

 NSArray *currentMetarArray = metarJson[@"weatherObservation"];
 for (NSDictionary *metaritem in currentMetarArray)

These lines are wrong. currentMetarArray is a dictionary, not array, it contains string key & value, so you should access it like in following way-

NSDictionary *jsonDictionary = [NSJSONSerialization JSONObjectWithData:data options:0 error:&error]; NSDictionary *weatherObservation = [jsonDictionary objectForKey:@"weatherObservation"];

then to get nCloud, use like NSString *nClouds = [weatherObservation objectForKey:@"clouds"];

Answer 3

The error thrown is the best clue for how you can fix this.

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFString objectForKey:]: unrecognized selector sent to instance 0x7f9298554560'

What this means is that you're thinking an object is a dictionary when in reality it isn't.

You can combat this using NSObject methods such as:

[myObject respondsToSelector:(@selector(objectForKey:))]; // will return a boolean value.

to see if the object will respond to the method you hope to send it

or

[myObject isKindOfClass:[NSDictionary class]]; // will return a boolean value.

to determine if the object is a NSDictionary.

What's likely happening, though, is that you have an error in expectation with the Deserialized JSON Data.

Happy bug hunting!