如何在iOS应用程序的后台发出间歇性的HTTP POST请求-Swift

Question

Hi I'm making an app that sends POST location update requests to a web application. I have one function called locationUpdate that I'd like to call intermittently once the app is in the background however I have't found a way to do it yet.

I have all the basics like Allow Location Always set. The app currently makes one HTTP POST request right when it enters the background because of this code in the AppDelegate file:

 func applicationDidEnterBackground(_ application: UIApplication) {

    sendLocation.determineCurrentLocation()
}

I also have this in the AppDelegate because I've seen it in a few stack overflow answers:

 func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    UIApplication.shared.setMinimumBackgroundFetchInterval(UIApplicationBackgroundFetchIntervalMinimum)
    return true
}

So all this but the app doesn't call sendLocation.determineCurrentLocation() (The function that makes the POST request) more than once and that is when the app is closed.

Can anyone tell me how to implement intermittent calling of the sendLocation function?

EDITED to show my locationManager:

 func determineCurrentLocation(){

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


    if CLLocationManager.locationServicesEnabled(){
        DispatchQueue.main.async {

            self.locationManager.requestLocation()
        }

    }
    else if (!CLLocationManager.locationServicesEnabled())
    {
        print("You need to enable location services to use this app")

    }




}
func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]){
    locationManager.stopUpdatingLocation()
    userLocation = locations[0] as CLLocation
    locationStruct.latitude=userLocation?.coordinate.latitude
    locationStruct.longitude=userLocation?.coordinate.longitude



    print(userLocation?.coordinate.latitude)
    print(userLocation?.coordinate.longitude)

    sendLocationPost()


}

Answer 1

You won't be able to do what you are trying to do unless you set up your app as a turn-by-turn navigation app and ask for permission to get location updates in the background.

Apps only get a very short time in the background before they are suspended.

You can ask for more background time with the beginBackgroundTask(expirationHandler:) call, but that's normally limited to 3 minutes of background time at max. (Search on that method to find the docs about it.)

Only certain types of apps are allowed to run indefinitely in the background. (Turn-by-turn navigation apps and streaming music apps.) You have to set up your info.plist to declare that your app is one of those types of apps. That is documented in the iOS docs that come with Xcode.

EDIT:

As Paul points out in his comment, you CAN ask for "always" location update permission and then ask for significant location change updates, although those are rather crude and you can't control the time interval between location updates (and won't get any updates until the OS decides the user has moved a significant distance.)