How can I know my app is working in background?

Question

I have written this program, it is work when the app is displaying on screen

If the app in background, it stop to print the latitude, when I resume the app, it will start to print again.

I have enabled background modes in xcode, and also checked Location updates, why my app still not running in background?

If the app is running, just the print function does not work in background, how can I know the app is running?

class ViewController: UIViewController,
    CLLocationManagerDelegate {

    var locationManager: CLLocationManager = CLLocationManager()
    var startLocation: CLLocation!

    func locationManager(_ manager: CLLocationManager,
                         didUpdateLocations locations: [CLLocation])
    {
        let latestLocation: CLLocation = locations[locations.count - 1]
        print(latestLocation.coordinate.latitude)    
    }

    override func viewDidLoad() {
        locationManager.desiredAccuracy = kCLLocationAccuracyBest
        locationManager.delegate = self
        locationManager.requestWhenInUseAuthorization()
        locationManager.startUpdatingLocation()
        startLocation = nil

    }
}

You have only requested "when in use" permission, so your app will not obtain location when it is in the background. For that you need to request "Always" permission — Paulw11, May 08 '17 at 03:35
Now I use `requestAlwaysAuthorization()`, it is still not running in background — CL So, May 08 '17 at 03:58
Did you add the required usage string to your info.plist? Are you being promoted for "always" permission? Is this view controller active when your app is suspended? — Paulw11, May 08 '17 at 04:06

score 2 · Answer 1 · answered May 08 '17 at 04:05

First, your problem:

locationManager.requestWhenInUseAuthorization()

This requests your location manager to update its location only when your app is in the foreground. You have to change this to:

locationManager.requestAlwaysAuthorization()

If it still doesn't work, make sure your location manager is firing updates at all by adding a print statement in the delegate functions.

Second, how to print stuff in the background:

My favorite way is to log things in UserDefaults, because those persist across app restarts. I will set my print statements as the value to a log key for example. Upon restart I will read the contents of UserDefaults from the log key.

KKRocks · Accepted Answer · 2017-05-08T14:46:43.087

1

If your app uses location in the background ).you have to set allowsBackgroundLocationUpdates to YES in addition to setting the background mode capability in Info.plist. Otherwise location updates are only delivered in foreground.

if CLLocationManager is first called startUpdatingLocation method, and in the projectname-Info.plist file is added Required Background Modes -> App registers for location updates.

edited May 08 '17 at 14:46

answered May 08 '17 at 04:15

KKRocks

8,222
1
18
84

It is work if I set `allowsBackgroundLocationUpdates` to true. But what do you mean `without showing the blue status bar`? Do you mean the blue bar can be hidden if I set `allowsBackgroundLocationUpdates`? But now the blue bar is showing. – CL So May 08 '17 at 14:22

How can I know my app is working in background?

2 Answers2