network activity indicator not appearing in iOS app - ios

Question

In my iOS app, I want to show the network activity indicator in the top status bar.
I've added the following:
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];
But the activity indicator never appears.
Does anyone know what might be wrong?
Here is the full code:
-(void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:YES];
// load sets
[self loadSets];
}
-(void)loadSets{
dispatch_async(dispatch_get_main_queue(), ^{
NSLog(#"in loadSets");
// show loading animation
UIView *loadingView = loadingIndicator;
loadingView.center = CGPointMake(screenWidth/2, screenHeight/2);
[self.view addSubview:loadingView];
[loadingIndicator startAnimating];
self.userSets = [[NSMutableArray alloc]init]; // re-initialize userSets
dispatch_async(bgQueue, ^{
NSString *userURLString = [userBaseUrl stringByAppendingFormat:#"/%#.json?auth_token=%#", username, auth_token];
NSLog(#"userURLString %#", userURLString);
NSURL *userURL = [NSURL URLWithString:userURLString];
NSData * userData = [NSData dataWithContentsOfURL:userURL];
dispatch_async(dispatch_get_main_queue(), ^{
if(userData){
[self fetchSets:userData];
// remove loading animation
[loadingView removeFromSuperview];
}else{
// error with authentication - should log out and require relogin
// [self logoutClick];
}
});
});
});
}
-(void)fetchSets:(NSData *)responseData{
NSError * error;
NSDictionary * json = [NSJSONSerialization
JSONObjectWithData:responseData
options:kNilOptions
error:&error];
if(json){
NSArray *sets = [json objectForKey:#"sets"];
for (NSDictionary *currentSet in sets){
Set *userSet = [[Set alloc] init];
userSet.name = [currentSet objectForKey:#"name"];
userSet.videoURL = [[currentSet objectForKey:#"media"] objectForKey:#"mp4"];
userSet.gifURL = [[currentSet objectForKey:#"media"] objectForKey:#"gif"];
userSet.imgURL = [[currentSet objectForKeyedSubscript:#"media"] objectForKey:#"img"];
userSet.setID = [currentSet objectForKey:#"id"];
[self.userSets addObject: userSet];
}
NSLog(#"trying to reload table data with userSets length %d", [self.userSets count]);
[self.collectionView reloadData];
dispatch_async(dispatch_get_main_queue(), ^{
NSLog(#"done loading table data");
});
}
}