Possible Object Deallocation Error, Background App Crash block_invoke_5 - ios

Question

I am having an unexpected issue with a crash on my app which I am specifically struggling to debug because it occurs in background at a time determined by the iOS system. I have some capitalised comments to the code which show where the issue is being back traced to. I hope this is clear.
I believe it has to do with object deallocation.
I have tried using the __block before initialising the object but
this has not helped.
I have also tried dispatching the lines of code
in error to the main queue but that has not helped.
The actual crash is listed as AppName: __66-[BackgroundUpdateController initiateBackgroundHealthkitObservers]_block_invoke_5 + 160
I apologise if some of the code does not fit standard formatting and conventions. I am self taught from a variety of places and so do not have proper experience with code format.
Many Thanks
#import "BackgroundUpdateController.h"
NSUserDefaults *backgroundDefaults;
#implementation BackgroundUpdateController
-(id)init{
backgroundDefaults = [[NSUserDefaults alloc] initWithSuiteName:#"group.HeartAnalyzer"];
return [super init];
}
-(void)initiateBackgroundHealthkitObservers{
// Check we should be running here
if(([backgroundDefaults integerForKey:#"sleepAnalysisEnabled"] != 1) || (![backgroundDefaults boolForKey:#"AutomaticSleepAdd"])) return;
// Initiate some variables, Use __block to ensure the backgroundHealthStore object does not get deallocated
__block HKHealthStore *backgroundHealthStore = [[HKHealthStore alloc] init];
HKQuantityType *activeEnergy = [HKObjectType quantityTypeForIdentifier:HKQuantityTypeIdentifierActiveEnergyBurned];
// Enable background delivery of active energy data from HealthKit
[backgroundHealthStore enableBackgroundDeliveryForType:activeEnergy frequency:HKUpdateFrequencyHourly withCompletion:^(BOOL success, NSError *error) {
}];
// Now setup an HKOberverQuery which triggers hourly if there are new active energy data points in HealthKit
HKObserverQuery *query = [[HKObserverQuery alloc] initWithSampleType:activeEnergy predicate:nil updateHandler:^(HKObserverQuery *query, HKObserverQueryCompletionHandler completionHandler, NSError *error) {
UIApplicationState state = [[UIApplication sharedApplication] applicationState];
if (state == UIApplicationStateBackground || state == UIApplicationStateInactive){// Only run when app is not in foreground
// Load some more variables with checks to ensure they are valid objects
NSDate *previousSavedDate = [backgroundDefaults objectForKey:#"DateBackgroundSleepLastSaved"];
if(previousSavedDate == nil) previousSavedDate = [NSDate distantPast];
NSDate *lastSleepCheck = [backgroundDefaults objectForKey:#"LastSleepCheck"];
if(lastSleepCheck == nil) lastSleepCheck = [NSDate distantPast];
// If the last save date was long enough ago and the last sleep check was long enough ago, proceed
if(([previousSavedDate timeIntervalSinceNow] < -(3600*18)) && ([lastSleepCheck timeIntervalSinceNow] < -(3600*2))){
[backgroundDefaults setObject:[NSDate date] forKey:#"LastSleepCheck"];
[backgroundDefaults setBool:NO forKey:#"BackgroundSleepFound"];
SleepTimesCalculator *sleepClass = [[SleepTimesCalculator alloc] init];
[sleepClass calculateSleepTimes:^{
NSLog(#"Background sleep time calculations complete");
if([backgroundDefaults boolForKey:#"BackgroundSleepFound"]){// Only continue is a sleep time was found
__block NSMutableArray *savedSleepObjects = [backgroundDefaults valueForKey:#"SleepTimesDataBase"];
if(savedSleepObjects.count > 0){
__block NSMutableDictionary *sleepObject = [savedSleepObjects objectAtIndex:0]; // THE __BLOCK USED TO PREVENT THE OBJECT BEING DEALLOCATED, STILL SEEMS TO BE BASED ON THE CRASH
NSDate *sleepStart = [NSDate dateWithTimeIntervalSinceReferenceDate:[[sleepObject valueForKey:#"CalculatedSleepTime"]integerValue]];// Get the sleep time start date object
NSDate *sleepEnd = [NSDate dateWithTimeIntervalSinceReferenceDate:[[sleepObject valueForKey:#"CalculatedWakeTime"]integerValue]];
NSInteger sleepSavedToHealth = [[sleepObject valueForKey:#"SavedToHealth"] integerValue];// Check its not already been saved by some other element of the app
if(sleepSavedToHealth != 1){
HKCategorySample *sleepSample = [HKCategorySample categorySampleWithType:[HKCategoryType categoryTypeForIdentifier:HKCategoryTypeIdentifierSleepAnalysis] value:1 startDate:sleepStart endDate:sleepEnd];// Generate sleep object for HealthKit
[backgroundHealthStore saveObject:sleepSample withCompletion:^(BOOL success, NSError *error) {
if (!success) NSLog(#"Uncommon Error! saveObject:sleepSample");
else{
dispatch_async(dispatch_get_main_queue(), ^{// DISPATCH TO MAIN QUEUE AN ATTEMPTED FIX FOR CRASH
sleepObject = [savedSleepObjects objectAtIndex:0];// Choose the most recent sleep time to save
[sleepObject setValue:[NSNumber numberWithInteger:1] forKey:#"SavedToHealth"];// THIS IS WHERE THE 'Last Exception Backtrace (0)' ENDS UP
[savedSleepObjects replaceObjectAtIndex:0 withObject:sleepObject];// Replace the object which now has the 'Saved' tag
[backgroundDefaults setObject:[NSDate date] forKey:#"DateBackgroundSleepLastSaved"];// Save the data of the last time we reached this point
[backgroundDefaults setObject:savedSleepObjects forKey:#"SleepTimesDataBase"];// Save the sleep times back to the database
});
}
}];
}
completionHandler();// Call the completion handler as we've been throught the sleepObjects array
}
else completionHandler();// Call the completion handler anyway
}
else completionHandler();// Call the completion handler anyway
}];
}
else completionHandler();
}
}];
[backgroundHealthStore executeQuery:query];// Execute the HealthKit healthstore query
}
#end

Answer 1

Prefixing __block does not guarantees existence of an object for #"CalculatedSleepTime" key in sleepObject
I think you have misinterpreted how __block works. This will be a great guide.
On a quick overview of the code, it seems like [sleepObject valueForKey:#"CalculatedSleepTime"] is returning nil & without a nullability check you are trying to extract the integerValue
So, consider:
NSMutableDictionary *sleepObject = [savedSleepObjects objectAtIndex:0];
id calculatedSleepTime = [sleepObject valueForKey:#"CalculatedSleepTime"];
if(calculatedSleepTime){
NSDate *sleepStart = [NSDate dateWithTimeIntervalSinceReferenceDate:[calculatedSleepTime integerValue]];
}
And it looks like you also don't require the __block prefix in HKHealthStore *backgroundHealthStore = [[HKHealthStore alloc] init];