What am I implementing incorrectly with NSDictionary & JSON serialization & NSUserDefaults?

Question

I think my error has to do with me not implementing my NSDictionary properly. Below is the error code I'm getting.

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFDictionary bytes]: unrecognized selector sent to instance 0x16eab400'

The error happens in the following method:

- (void)check:(NSData *)json{ 
NSDictionary *json1 = [NSJSONSerialization
                     JSONObjectWithData:json
                      options:kNilOptions
                      error:nil];

NSUserDefaults *userdefaluts = [NSUserDefaults standardUserDefaults];
[userdefaluts setObject:[json1 objectForKey:@"Name"] forKey:@"name"];
[userdefaluts setObject:[json1 objectForKey:KEY_USER_ID] forKey:KEY_USER_ID];

NSLog(@"MainView - check - name: %@",[userdefaluts objectForKey:@"name"]);
NSLog(@"MainView - check - name: %@",[userdefaluts objectForKey:KEY_USER_ID]);
}

Answer 1

So the answer was quite easy. All I had to do was change the data type coming in to NSDictionary. Below is the correct code.

- (void)check:(NSDictionary *)json{ 
NSDictionary *json1 = [NSJSONSerialization
                 JSONObjectWithData:json
                  options:kNilOptions
                  error:nil];

NSUserDefaults *userdefaluts = [NSUserDefaults standardUserDefaults];
[userdefaluts setObject:[json1 objectForKey:@"Name"] forKey:@"name"];
[userdefaluts setObject:[json1 objectForKey:KEY_USER_ID] forKey:KEY_USER_ID];

NSLog(@"MainView - check - name: %@",[userdefaluts objectForKey:@"name"]);
NSLog(@"MainView - check - name: %@",[userdefaluts objectForKey:KEY_USER_ID]);
}

Answer 2

Possibilities: Your code might run on a background thread and NSUserDefaults doesn't like it. One of the objectForKey calls on json1 returns nil and things go wrong. I'd store the two [json1 objectForKey:...] results in a local variable and NSLog them. Step through the code in the debugger step by step.

And the big possibility: The object "json" that you are passing in isn't actually NSData. Do an NSLog on it and check what it really is. It might be an NSDictionary* and not an NSData*, which would explain why a method used for NSData (length) is sent to an NSDictionary. Check the call to the method. Are you passing an object of type "id"?

Answer 3

Your data is probably wrong and NSJSONSerializer cannot parse it, try this to show if there is an error : NSError *jsonError; NSDictionary *json1 = [NSJSONSerialization JSONObjectWithData:json options:kNilOptions error:&jsonError]; if(jsonError){ NSLog(@"could not parse json data, error : %@",jsonError.localizedDescription); }