NSMangedObject subclass method called constantly after changing NSFetchedResultsController NSPredicate - ios

Question

I've been stuck with this and cannot find the culprit. I will try to include as much useful code that I can. See bottom for TL;DR version.
IDEA
User opens the app, you can find restaurants in a certain city OR set it to find the restaurants near your location (assuming you allowed the app to see your location). If you set the city, then the NSFetchedResultsController performs a fetch with a certain NSPredicate. When you tap on the button to find the restaurants near you, it changed the NSPredicate and executes the fetch again.
SET UP
1) When my UIViewController is loaded, it called a method on a subclass of NSUserDefaults to grab the user's current location.
2) This method tells a CLLocationManager object to start updating the user's location, once it has updated the location, the didUpdateLocations method gets called.
3) Since I have .desiredAccuracy set to kCLLocationAccuracyBest the didUpdateLocations method gets called often, so I set a timer to perform a method called updateRestaurantDistance which performs a fetch on the main NSManagedObjectContext and retrieves all the restaurants in the database.
4) A loop iterates through each restaurant and calls a method to set the restaurant's distance from the user.
5) Once the loop is finished, I save the context with the updated values.
ISSUE
Everything runs fine when I start the app, and once the fetch from 4) is finished iterating through each item, I can tap the button that fetches the restaurants that are near me.
However, if the iterations from 4) aren't finished, and I tap the button that finds the restaurants near me, the iterations finish, but the context is not saved (I have print statements set up) and the method that updates the restaurant distance is called infinitely blocking the main thread and making the UI unusable.
CODE
- UIViewController
override func viewDidLoad() {
super.viewDidLoad()
//configure properties
//core data
context = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext
//fetch controller
fetchController.delegate = self
//default values
user = User()
self.user.getCurrentLocation()
}
//method that is called when the button to filter restaurants near user is tapped
func nearMe() {
restaurantPredicate = NSPredicate(format: "(distance < %f AND distance > %f) AND SUBQUERY(specials,$s, ($s.type LIKE %# OR $s.type LIKE %#) AND $s.day LIKE %#).#count > 0",
user.doubleForKey(UserData.MaxDistance.rawValue), 0.01, typeQuery!, "Combo", day)
fetchController.fetchRequest.sortDescriptors = [distSort,nameSort,citySort]
do {
try fetchController.performFetch()
} catch {
print("Error fetching when sorting by near me")
}
tableView.reloadData()
}
The User class that has the method to get location
func getCurrentLocation() {
//ask for access to location (if not given)
if CLLocationManager.locationServicesEnabled() {
locationManager.requestWhenInUseAuthorization()
}
//if allowed, start checking for location
if CLLocationManager.authorizationStatus() == .AuthorizedWhenInUse {
locationManager.delegate = self
locationManager.desiredAccuracy = kCLLocationAccuracyBest
locationManager.startUpdatingLocation()
}
}
The CLLocationDelegate
func locationManager(manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
// get coordintes
if let locValue: CLLocationCoordinate2D = manager.location?.coordinate {
//check if timer has started
if timer == nil {
timer = NSTimer.scheduledTimerWithTimeInterval(1.0, target: self, selector: "updateRestaurantDistance", userInfo: nil, repeats: false)
} else {
timer?.invalidate()
timer = NSTimer.scheduledTimerWithTimeInterval(1.0, target: self, selector: "updateRestaurantDistance", userInfo: nil, repeats: false)
}
//stop updating since we're done
locationManager.stopUpdatingLocation()
}
}
Update location method
func updateRestaurantDistance() {
let fetch = NSFetchRequest(entityName: "Restaurant")
let context = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext
do {
let results = try context.executeFetchRequest(fetch) as! [Restaurant]
for result in results {
print(results.indexOf(result))
result.getDistance()
}
} catch {
print("Error updating restaurant distances from UserClass")
}
do {
try context.save()
print("saved context")
} catch {
print("error saving context while updating restaurant distance: \(error)")
}
}
The Restaurant methods
//This method gets called infinitely and I have no idea why
func getDistance() {
print("getDistance")
guard CLLocationManager.authorizationStatus() == .AuthorizedWhenInUse else {
return
}
self.distance = self.getDistanceFromRestaurant()
}
func getDistanceFromRestaurant() -> CLLocationDistance {
let user = User()
guard CLLocationManager.authorizationStatus() == .AuthorizedWhenInUse else {
return Double(0)
}
let longitude = user.doubleForKey(UserData.Longitute.rawValue)
let latitude = user.doubleForKey(UserData.Latitude.rawValue)
guard abs(longitude) + abs(latitude) > 0 else {
return Double(0)
}
let loc = CLLocation(latitude: latitude, longitude: longitude)
let selfLoc = CLLocation(latitude: Double(self.latitude), longitude: Double(self.longitude))
return loc.distanceFromLocation(selfLoc) / 1000
}
Happy to add more if needed, thank you!
EDIT: Seems that it gets to try context.save() in updateRestaurantDistance() and starts the loop there (aka it doesn't get to the print statement
EDIT 2: TL;DR Code version:
This updates the restaurant's distance to the user, trys are in do-catch blocks but removed for simplicity
func updateRestaurantDistance() {
let fetch = NSFetchRequest(entityName: "Restaurant")
let context = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext
let results = try context.executeFetchRequest(fetch) as! [Restaurant]
for result in results {
result.getDistance()
}
try context.save()
}
func getDistance() {
self.distance = 10 // method to calculate distance is called, but for simplicity set to 10
}
While updateResturantDistance is running, I cannot change the NSPredicate to anything with a distance attribute and perform a fetch for my NSFetchedResultsController i.e:
predicate = NSPredicate(format: "distance < %f", 10)
fetchController.fetchRequest.predicate = predicate
try fetchController.performFetch
doesn't work, but
predicate = NSPredicate(format: "city LIKE %#", "New York")
fetchController.fetchRequest.predicate = predicate
try fetchController.performFetch
works

Answer 1

Either
disable the UI control that causes the reload until everything is finished
or
keep a Bool variable around indicating if you are looping through the locations. When the control is hit, change this variable. In the loop check the variable and abort if it has changed and start from scratch without saving.

Answer 2

OH. MY. GOODNESS.
WOW
So let's recall getters and setters. In most programming languages that aren't like swift i.e Java, you must create them with methods i.e
private var distance = 1
getDistance() -> Int {
return self.distance
}
But in swift, this isn't necessary. Anyways, turns out my getDistance method was being called for my NSPredicate. I changed the name of the method to getRestaurantDistance and everything runs as expected. Do not be like my and name methods that would also be named the getter and setter.