json populate table view controller wont work - ios

Question

I've been following a tutorial on youtube on how to load external data from a database on to a iOS application. I understand the concept and how it works etc. But I'm having an error even though I'm following the video and from looking online it seems to be a common error.
- (void) retrieveData
{
NSURL * url = [NSURL URLWithString: getDataURL];
NSData * data = [NSData dataWithContentsOfURL:url];
jsonArray = [NSJSONSerialization JSONObjectWithData: data options:kNilOptions error:nil];
//set up our cities array
citiesArray = [[NSMutableArray alloc] init];
// loop through our json array
for (int i =0; i< jsonArray.count; i++)
{
//create our city object
NSString * cID = [[jsonArray objectAtIndex:i] objectForKey:#"id"];
NSString * cName = [[jsonArray objectAtIndex:i] objectForKey:#"cityName"];
NSString * cState = [[jsonArray objectAtIndex:i] objectForKey:#"cityState"];
NSString * cPopulation = [[jsonArray objectAtIndex:i] objectForKey:#"cityPopulation"];
NSString * cCountry = [[jsonArray objectAtIndex:i] objectForKey:#"country"];
// Add the city object to our cities array
[citiesArray addObject:[[City alloc]initWithCityName:cName andCityState:cState andCityCountry:cCountry andCityPopulation:cPopulation andCityID:cID]];
}
//reload our table view
[self.tableView reloadData];
}
The code fails on the third line.
jsonArray = [NSJSONSerialization JSONObjectWithData: data options:kNilOptions error:nil];
Why is that? Any suggestions? The jsonArray has already been created, so I can't understand why it won't work.

Answer 1

I checked your code & i don't think there is any error.
I hope you've declared NSMutableArray *jsonArray in header (.h) file.
If you getting error in thos line :
jsonArray = [NSJSONSerialization JSONObjectWithData: data options:kNilOptions error:nil];
than replace kNilOptions with simply nil.
If you getting crash than it might be because nil data. In that case you have to put condition before you store data in array something like this :
if (data != nil)
{
jsonArray = [NSJSONSerialization JSONObjectWithData: data options:nil error:nil];}
Hope it'll help.