Question

I am trying to centralize Core Data calls for each Core Data entity into a Helper Class. Each Helper class contains the entity’s fetch, update, and insert methods. For one entity helper class, I am getting a memory leak when I profile the application at this line:

NSArray *results = [managedObjectContext executeFetchRequest:request error:&error];

ARC is turned on and the leak appears after the view has been unloaded.

Here are the associated ViewController and Helper Class code:

ViewController.m:

@synthesize location // and other properties...;

- (void)viewDidLoad
{
    [self loadLocation];
    [super viewDidLoad];
}

- (void)viewDidUnload 
{
    // Set properties to nil here

    [super viewDidUnload];
}

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
}

- (void)loadLocation
{
    if (self.locationID.intValue > 0)
    {
        LocationCoreDataHelper *helper = [[LocationCoreDataHelper alloc] init];
        self.location = [helper selectLocationWithPredicate:[NSString stringWithFormat:@"id = %d", self.locationID.intValue]];

        if(self.location)
        {
            // Create a new coordinate of the user's location
            CLLocationCoordinate2D coord;
            coord.latitude = [self.location.latitude doubleValue];
            coord.longitude =[self.location.longitude doubleValue];

            // Annotate the point with user's information
            MKPointAnnotation *point = [[MKPointAnnotation alloc] init];
            point.coordinate = coord;
            point.title = self.location.title;
            point.subtitle = self.location.subtitle;

            // Add the annotated point
            [mkMap addAnnotation:point];  

            // Set the viewable region of the map
            MKCoordinateRegion region = MKCoordinateRegionMakeWithDistance(point.coordinate, 5000, 5000);

            [mkMap setRegion:region animated:YES]; 
        }

        helper = nil;
    }
}

The location property is defined as the entity’s managed object class.

LocationCoreDataHelper.m:

@implementation LocationCoreDataHelper

- (id)init
{
    if(self = [super init])
    {
        // Setup the core data manager if needed
        if(managedObjectContext == Nil)
        {
            managedObjectContext = [(AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];
        }        
    }

    return self;
}

- (Location *)selectLocationWithPredicate:(NSString *)predicateString
{
    NSError *error = nil;

    // Build the entity and request
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Location" inManagedObjectContext:managedObjectContext];
    NSFetchRequest *request = [[NSFetchRequest alloc] init];
    [request setEntity:entity];

    if(predicateString)
    {
        // Set the search criteria
        NSPredicate *predicate = [NSPredicate predicateWithFormat:predicateString];
        [request setPredicate:predicate];
    }

    // Perform the search
    // LEAK HERE
    NSArray *results = [managedObjectContext executeFetchRequest:request error:&error];  

    if(results.count >0)
    {
        return (Location *)[results lastObject];
    }
    else
    {
        return nil;
    }
}

// Other methods here
@end

I can’t figure out why the memory leak is occurring there. Any ideas?

UPDATE #1:

If I replace this:

point.coordinate = coord;
point.title = self.location.title;
point.subtitle = self.location.subtitle;

with this:

point.coordinate = coord;
point.title = @"Title";
point.subtitle = @"Subtitle";

NSLog(@"%@", self.location.title);

I do not get the memory leak. Why is that?

Answer 1

Thanks to Inafziger for pointing me in the right direction. I ended up having to create a custom MKAnnotation class like so:

#import <Foundation/Foundation.h>
#import <MapKit/MapKit.h>

@interface MyAnnotation : NSObject <MKAnnotation>

@property (nonatomic, readonly) CLLocationCoordinate2D coordinate;
@property (nonatomic, copy, readonly) NSString *title;
@property (nonatomic, copy, readonly) NSString *subtitle;

- (id) initWithCoordinates:(CLLocationCoordinate2D)paramCoordinates
                     title:(NSString *)paramTitle
                     subTitle:(NSString *)paramSubTitle;

@end

and I updated my View Controller like so:

MyAnnotation *point = [[MyAnnotation alloc] initWithCoordinates:coord
                                                          title:self.location.title
                                                       subTitle:self.location.subtitle];

By implementing the custom annotation class in this manner, it solved the issue of the memory leak. I’m still not a 100% sure why Instruments pointed the leak to the Core Data call. Perhaps because that is where the NSManagedObject originated and that wasn’t what was getting released properly?