Location tracking stops after a while when app is

问题:

I've created a simple app which tracks user location and creates local notification for every time location is updated.

I enabled the background modes below,

let locationManager = CLLocationManager()

open override func viewDidLoad() {
       locationManager.delegate = self;
       locationManager.desiredAccuracy = kCLLocationAccuracyBest;
       locationManager.distanceFilter = 10
       locationManager.allowsBackgroundLocationUpdates = true
       locationManager.startUpdatingLocation()
}

open func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
       let notification = UILocalNotification()
       notification.alertBody = "location updated"
       notification.fireDate = Date()
       UIApplication.shared.scheduleLocalNotification(notification)
}

I set string for NSLocationAlwaysUsageDescription and ask for permission. User grant permission for always usage when the app loaded first time.

---

It's working well when app is in the foreground, when it goes background still working at least in 5-40 minutes time range which is changeable by battery or other opened apps.

The problem is why it stops working, doesn't it expected to be keep working?

I've never seen a time limit in Apple docs.

回答1:

Switch to significant location updates when the app moves to background. iOS will unload the app if it keep alive in the background indefinitely.

locationManager.pausesLocationUpdatesAutomatically = false

回答2:

Reduce Accuracy

Set the desiredAccuracy property of the location manager object

self.locationManager.desiredAccuracy = kCLLocationAccuracyBestForNavigation

You can use one of the CLLocationAccuracy constants

IMPORTANT

By default, standard location updates on iOS devices run with an accuracy level of best. Change these settings to match your app’s requirements. Otherwise, your app will unnecessarily waste energy.

---

Auto-Pause

Set the pausesLocationUpdatesAutomatically property of the location manager object to true

self.locationManager.pausesLocationUpdatesAutomatically = true

IMPORTANT

For apps that have in-use authorization, a pause to location updates ends access to location changes until the app is launched again and able to restart those updates. If you do not wish location updates to stop entirely, consider disabling this property and changing location accuracy to kCLLocationAccuracyThreeKilometers when your app moves to the background. Doing so allows you to continue receiving location updates in a power-friendly manner.

---

Allow background updates

Set the allowsBackgroundLocationUpdates property of the location manager object to true

self.locationManager.allowsBackgroundLocationUpdates = true

Apps that want to receive location updates when suspended must include the UIBackgroundModes key (with the location value) in their app’s Info.plist file and set the value of this property to true. The presence of the UIBackgroundModes key with the location value is required for background updates

---

Specify an Activity Type

Set the activityType property to let Core Location know what type of location activity your app is performing at a given time

self.locationManager.activityType = .automotiveNavigation 

You can use one of the CLActivityType cases

---

Defer Location Update

On supported devices with GPS hardware, you can let the location manager defer the delivery of location updates when your app is in the background. For example, a fitness app that tracks the user’s location on a hiking trail can defer updates until the user has moved a certain distance or a certain period of time has elapsed.

---

• Energy Efficiency Guide for iOS Apps - Location Best Practices
• GettingLocationWhenSuspended

回答3:

After searching for references (talking about any limitation), I assume that Apple Core Location Best Practices video session could be useful! at 06:53 talking about standard location in the background:

furthermore, Core Location won't take any action to ensure your app continues to run, so if you have background run for some reason and you decide to start a location session you might get some updates, but you might also get suspended before you receive all information that you hope to receive...

Actually, I faced this issue before, -as a workaround- the core location was used to keep tracking the location of the user to do unrelated functionality to its location -which is uploading files-, but this workaround didn't work since iOS 9 has been released; I even posted a question referring to this issue.

However, it seems your case is not identical to what I faced, if you are aiming to:

... creates local notification for every time location is updated.

then you might need to follow the approach of integrating with User Notification Framework - UNLocationNotificationTrigger:

The geographic location that the user must reach to enable the delivery of a local notification.

It is also mentioned in the video session (08:59).

Probably, this is could be not what are you looking for, but since we have no guarantee that the background execution will continue running, you might -somehow- find a way to integrate it in your app to achieve the desired functionality.

Update for iOS 11:

You might need to check this answer for the proper way to request the location access.

回答4:

By the sound of it the app is being killed due to memory constraints. It should however be re-launched when a new location becomes available, as described here: https://developer.apple.com/documentation/uikit/uiapplicationlaunchoptionskey/1623101-location

You should see application(_:didFinishLaunchingWithOptions:) being called, and the 'location' key should be present in the launch options. You'll can then re-create whatever is consuming the locations and continue recording.

If it's not being re-launched it could be too memory hungry. Check the memory consumption of the app and see if applicationDidReceiveMemoryWarning(_:) is being called.

回答5:

I assume you haven't implement background task. You can read here.

In the above link under section "Implementing Long-Running Tasks" point no. 3 is your situation, so it's valid you can use background location update in your project and for same you need to implement a background task too.

There are three way to track user location(as per above link under section "Tracking the User’s Location" ) :-

1. Foreground-only location services (which works in your case)
2. The significant-change location service (Recommended), but I think it is not usable in your case as you want to update user location per 10 meter and it works for ~500 meters, for more please see here
3. Background location services (I think you are trying for this) and solution is to add a background task.

Below is example of background task and you can modify as per your requirement, it works for me since last 2 hours and my app still update location in background.

.

In your AppDelegate class please update below function and then run your app in background.

func applicationDidEnterBackground(_ application: UIApplication) {
    application.beginBackgroundTask(withName: "") {}
}

And below is my ViewController class

import UIKit
import CoreLocation

class ViewController: UIViewController, CLLocationManagerDelegate {

    let locationManager = CLLocationManager()

    override func viewDidLoad() {
        super.viewDidLoad()

        locationManager.delegate = self;
        locationManager.requestAlwaysAuthorization()
        locationManager.desiredAccuracy = kCLLocationAccuracyBest;
        locationManager.allowsBackgroundLocationUpdates = true
        locationManager.distanceFilter = kCLDistanceFilterNone

        Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { (timer) in
            self.locationManager.startUpdatingLocation()
        }

    }

    func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
        print("didUpdateLocations \(Date())")
        self.locationManager.stopUpdatingLocation()
    }

}

回答6:

You need to do some changes in AppDelegate class ,launch method, applicationDidEnterBackground and applicationDidBecomeActive methods.

Create a sharedInstance for location manager.

FYI please go through this http://mobileoop.com/getting-location-updates-for-ios-7-and-8-when-the-app-is-killedterminatedsuspended

it might help you.Check comments as well.