iOS: Dictionary from / to json

NSError * error;
NSData * jsonData = [NSJSONSerialization dataWithJSONObject:response options:0 error:&err];
NSString * myString = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];

NSError * error;

    NSDictionary * response = (NSDictionary *)[NSJSONSerialization JSONObjectWithData:[myString dataUsingEncoding:NSUTF8StringEncoding] options:NSJSONReadingMutableContainers error:&error];