Plot Points from dictionary - objective-c

Question

I'm getting latitude, longitude and many other fields from the server.
I put each row from the database in a separate dictionary within a array.
I'm trying to map out a point from the latitude and longitude, but when I try to access the latitude by key I get a compiler error No visible #interface for NSDictionary....
Server Response
[{"id":1,"user_id":0,"latitude":"42.2367","longitude":"-71.11332","status":"active","responded_at":null,"created_at":"2015-04-13T12:52:51.144Z","updated_at":"2015-04-13T12:52:51.161Z"},{"id":2,"user_id":0,"latitude":"42.23497","longitude":"-71.11238","status":"active","responded_at":null,"created_at":"2015-04-13T12:57:03.000Z","updated_at":"2015-04-13T12:57:03.002Z"},{"id":3,"user_id":0,"latitude":"42.24222","longitude":"-71.11536","status":"active","responded_at":null,"created_at":"2015-04-13T12:57:49.012Z","updated_at":"2015-04-13T12:57:49.014Z"},{"id":4,"user_id":0,"latitude":"42.24194","longitude":"-71.11556","status":"active","responded_at":null,"created_at":"2015-04-13T13:03:10.710Z","updated_at":"2015-04-13T13:03:10.713Z"},{"id":5,"user_id":0,"latitude":"42.23493","longitude":"-71.11244","status":"active","responded_at":null,"created_at":"2015-04-13T13:05:39.713Z","updated_at":"2015-04-13T13:05:39.716Z"},{"id":6,"user_id":0,"latitude":"42.23598","longitude":"-71.11467","status":"active","responded_at":null,"created_at":"2015-04-13T13:08:12.983Z","updated_at":"2015-04-13T13:08:12.986Z"},{"id":7,"user_id":0,"latitude":"42.23598","longitude":"-71.11467","status":"active","responded_at":null,"created_at":"2015-04-13T13:08:38.115Z","updated_at":"2015-04-13T13:08:38.118Z"},{"id":8,"user_id":0,"latitude":"42.23794","longitude":"-71.11471","status":"active","responded_at":null,"created_at":"2015-04-13T13:10:11.593Z","updated_at":"2015-04-13T13:11:19.467Z"}]
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
// The request is complete and data has been received
// You can parse the stuff in your instance variable now
NSError *error;
NSMutableDictionary *json = [NSJSONSerialization
JSONObjectWithData:_responseData
options:NSJSONReadingMutableContainers|NSJSONReadingMutableLeaves
error:&error];
for (int i = 0; i < json.count; i++) {
double latitude = [[json objectAtIndex:i] objectForKey:#"latitude"];
double longitude = [[[json objectForKey:#"longitude"]objectAtIndex:i] doubleValue];
CLLocationCoordinate2D latlng = CLLocationCoordinate2DMake(latitude, longitude);
MKPointAnnotation *point = [[MKPointAnnotation alloc] init];
[point setCoordinate:latlng];
[worldView addAnnotation:point];
}
}

Answer 1

The server response (like you say in the question) is an array of dictionaries.
So json should be declared as an NSArray not an NSMutableDictionary.
This is what causes the compiler error No visible #interface for NSDictionary... because NSMutableDictionary does not have a objectAtIndex: method.
In addition, the code to get the longitude is backwards (it treats json like a dictionary and then tries to access an array inside the resulting key value).
The corrected code would be:
NSArray *json = [NSJSONSerialization
JSONObjectWithData:_responseData
options:NSJSONReadingMutableContainers|NSJSONReadingMutableLeaves
error:&error];
for (int i = 0; i < json.count; i++) {
NSDictionary *pointDictionary = [json objectAtIndex:i];
double latitude = [[pointDictionary objectForKey:#"latitude"] doubleValue];
double longitude = [[pointDictionary objectForKey:#"longitude"] doubleValue];
CLLocationCoordinate2D latlng = CLLocationCoordinate2DMake(latitude, longitude);
MKPointAnnotation *point = [[MKPointAnnotation alloc] init];
[point setCoordinate:latlng];
[worldView addAnnotation:point];
}