Completion block/callback on FetchRequest completion - iphone

Question

I have a FetchRequest in my model class named ContentManager. It fetches quite a lot of data, so the screen is blank until it's completion. In the ViewController that displays the fetched results, I would like to show a loading indicator, so I would like to get a callback when the FetchRequest has completed and pass that to the ViewController to stop the loading indicator. Is this possible?
Here is the FetchRequest from the ContentManager class:
- (NSArray*)recipesForMagazine
{
NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Recipe" inManagedObjectContext:managedObjectContext];
[request setEntity:entity];
NSString* path = [[NSBundle mainBundle] pathForResource:#"magazine_recipe_guids" ofType:#"plist"];
NSArray* recipeGuids = [NSArray arrayWithContentsOfFile:path];
NSPredicate* predicate = [NSPredicate predicateWithFormat:#"guid IN %#",recipeGuids];
[request setPredicate:predicate];
NSSortDescriptor* sort = [[NSSortDescriptor alloc] initWithKey:#"title" ascending:YES selector:#selector(localizedCaseInsensitiveCompare:)];
[request setSortDescriptors:[NSArray arrayWithObject:sort]];
[sort release];
NSError* error = nil;
NSArray* fetchResults = [managedObjectContext executeFetchRequest:request error:&error];
[request release];
return fetchResults;
}
Here I set it up in the ViewController
self.magazineRecipes = [[ContentManager defaultManager] recipesForMagazine];
I want to set up the fetchrequest method like this:
- (NSArray*)recipesForMagazine:(void (^)(BOOL success))block or something, so in the viewcontroller I can call it like this
self.magazineRecipes = [[CTContentManager defaultManager] recipesForMagazine:^(BOOL success) {
if (success) {
//stop activity indicator view
}
}];
I don't know if I'm at all in the right way of thinking, thanks for your help in advance!

Answer 1

I would make the viewController a delegate of the ContentManager class. So in the ContentManager.h I would do something like:
#protocol ContentManagerDelegate()
-(void) didFetchResults:(NSArray *) results;
-(void) didResultsFail: (NSError *) error;
#end
#interface ContentManager : <SuperClass Name>
-(id) initWithDelegate: (id<ContentManagerDelegate>) delegate;
#property (nonatomic, strong) id<ContentManagerDelegate> delegate;
#end
and in the implementation:
-(id) initWithDelegate: (id<ContentManagerDelegate>) delegate
{
self = [super init];
if(self)
{
_delegate = delegate;
}
return self;
}
and in your recipesForMagazine method you can use the delegate [_delegate didFetchResults: fetchResults], you can implement a method to pass errors to the delegate if you want as well. In your ViewController.h do #interface ViewController.h : UIViewController <ContentManagerDelegate> and in the implementation you should be able to implement the didFetchResults: method that will give you the results and in that method you can stop the activity indicator from animating.