Parsing JSON data to an array

Question

I get the following error whenI launch my app

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', 
    reason: '-   [COViewController fetchAppNetData]: unrecognized selector 
    sent to instance 0x716d200'

Basically I am unable to find out how to parse the JSON data to my array. The structure of my JSON is as follows

{

  "meta": {},

  "data": []

}

I know that meta is a dictionary and data is an array. But when I try to use the following piece of code I get the above error

- (void)fetchAppNetData:(NSData *)responseData
{
 //parse JSON data
 NSError *error;
 NSDictionary* appNet_json = [NSJSONSerialization 
    JSONObjectWithData:responseData options:kNilOptions error:&error];
 NSArray* appNetTimeline = [[appNet_json objectForKey:@"meta"] 
    objectForKey:@"data"];
 NSLog(@"AppNet Timeline : %@",appNetTimeline);
}

How do I make sure that I can identify the structure of JSON properly next time, so that I can avoid this sort of issue? I am extremely sorry to come up with such kind of doubts

Your error has nothing to do with parsing JSON. fetchAppNetData isn't defined in the object you're trying to use to call it. You never even get into the method. — Hot Licks
– Hot Licks, Commented Apr 27, 2013 at 3:04
I am calling definitely calling it in viewdidLoad [self performSelectorOnMainThread:@selector(fetchAppNetData) withObject:appNetData waitUntilDone:YES]; — BarryVenom
– BarryVenom, Commented Apr 27, 2013 at 3:12
Do you notice the : on the end of that selector name? Neither do I. — Hot Licks
– Hot Licks, Commented Apr 27, 2013 at 3:13
(And there's no need to do performSelectorOnMainThread. viewDidLoad is already in the main thread.) — Hot Licks
– Hot Licks, Commented Apr 27, 2013 at 3:14

Ken Thomases · Accepted Answer · 2013-04-27 03:05:58Z

3

The error has nothing to do with the content of the method -fetchAppNetData:. That method is not even getting called.

The error is saying that you tried to invoke a method of that name on an object that doesn't respond to it. You've sent that message to an instance of class COViewController, but that's evidently not the class that implemented the method you posted.

answered Apr 27, 2013 at 3:05

Ken Thomases

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4 Comments

BarryVenom Over a year ago

Caught the error. I forgot to add a : at the end of fetchAppNetData. Here is the corrected code

[self performSelectorOnMainThread:@selector(fetchAppNetData:) withObject:appNetData waitUntilDone:YES]; – BarryVenom 57 secs ago edit

Hot Licks Over a year ago

@BarryVenom -- Why are you doing the performSelector vs just calling the method??

BarryVenom Over a year ago

I had to do so because I wanted to download all the JSON data in the background while the application displays the first view to the user.

Ken Thomases Over a year ago

It seems odd that you are shunting data handling to the main thread. Usuallly, you do data parsing on the background thread and UI updates on the main thread. In any case, you might consider switching to GCD, which entails code which the compiler can more readily check. For example: dispatch_sync(dispatch_get_main_queue(), ^{ [self fetchAppNetData:appNetData]; }); Also, consider if you really need synchronization here. If not, use dispatch_async().

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