HKObserverQuery randomly called twice in a row

Question

I have an issue I'm trying to solve, I've setup an HKObserveryQuery, which works great and gathers new data for me.

The issue however is that sometimes when I go back to the Health app and delete an item after I've manually added it to the Health app, I notice the HKObserverQuery I've set up fires two times very closely together, which I'm trying to solve because I use this observer to later upload some data, and I don't want a duplicate.

I'd appreciate any help offered. Code:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    [self setup];

    return YES;
}

- (void)setup
{
    if ([HKHealthStore isHealthDataAvailable])
    {
        self.healthStore = [[HKHealthStore alloc]init];

        NSSet *readTypes = [NSSet setWithObject:[HKObjectType quantityTypeForIdentifier:HKQuantityTypeIdentifierHeartRate]];

        [self.healthStore requestAuthorizationToShareTypes:nil
                                                 readTypes:readTypes
                                                completion:^(BOOL success, NSError *error)
         {
             if (!error && success)
             {
                 [self observeHR];

                 [self.healthStore enableBackgroundDeliveryForType:
                 [HKQuantityType quantityTypeForIdentifier:HKQuantityTypeIdentifierHeartRate]
                 frequency:HKUpdateFrequencyImmediate withCompletion:^(BOOL success, NSError *error){}];
             }
         }];
    }
}

- (void)observeHR
{
    HKObserverQuery *query = [[HKObserverQuery alloc]initWithSampleType:[HKSampleType quantityTypeForIdentifier:HKQuantityTypeIdentifierHeartRate]
                        predicate:nil
    updateHandler:^(HKObserverQuery *query, HKObserverQueryCompletionHandler completionHandler, NSError *error)
    {
        if (!error)
        {   
            // Randomly called twice *VERY* close together
            NSLog(@"Query");
            [self queryWithCompletionHandler:completionHandler];
        }
        else
        {
            if (completionHandler)
            {
                completionHandler();
            }
        }
    }];

    [self.healthStore executeQuery:query];
}

Console output, notice the times: This occurs when only deleting one item from the Health app, which is incorrect.

2014-12-29 16:50:20.121 TestApp[174:5674] Query
2014-12-29 16:50:20.124 TestApp[174:5674] Query

Answer 1

I believe I've now fixed the issue by setting a BOOL flag to prevent a second bogus HKObserverQuery to be called, and eliminating duplicate processing for no reason. Code:

- (void)observeHR
{
    HKObserverQuery *query = [[HKObserverQuery alloc]initWithSampleType:[HKSampleType quantityTypeForIdentifier:HKQuantityTypeIdentifierHeartRate]
                        predicate:nil
    updateHandler:^(HKObserverQuery *query, HKObserverQueryCompletionHandler completionHandler, NSError *error)
    {
        if (!self.queryInProgress)
        {
            self.queryInProgress = YES;

            if (!error)
            {
                [self queryWithCompletionHandler:completionHandler];
            }
            else
            {
                self.queryInProgress = NO;

                if (completionHandler)
                {
                    completionHandler();
                }
            }
        }
        else
        {
            NSLog(@"Query already in progress");
        }
    }];

    [self.healthStore executeQuery:query];
}