IOS-位置更新间隔

Question

I'm starting on IOS developing, and I'm very unfamiliar with the language.

I'm trying to develop an app that will track the location of a device on the background. I've followed some tutorials and put up a code that Logs the location update.

-(void)CurrentLocationIdentifier
{
    locationManager = [CLLocationManager new];
    locationManager.delegate = self;
    locationManager.distanceFilter = kCLDistanceFilterNone;
    locationManager.desiredAccuracy = kCLLocationAccuracyBest;
    [locationManager startUpdatingLocation];
}

- (void)locationManager:(CLLocationManager *)manager
    didUpdateToLocation:(CLLocation *)newLocation
    fromLocation:(CLLocation *)oldLocation {

        NSLog(@"%@", newLocation);
}

- (void)applicationDidEnterBackground:(UIApplication *)application
{
    [self CurrentLocationIdentifier];
}

It works. Since I've configured the .plist file it is registered for running on background, it logs the location endlessly.

But I need the update to be periodically, with a defined interval, otherwise it would be a battery killer. I realize that there are tons of questions here on SO about Location Update on the background, but my attempts are not being successful and I'm stuck.

I've tried stoping the Update and scheduling a start with NSTimer within the location update listener:

- (void)locationManager:(CLLocationManager *)manager
    didUpdateToLocation:(CLLocation *)newLocation
    fromLocation:(CLLocation *)oldLocation {

        NSLog(@"%@", newLocation);

        [locationManager stopUpdatingLocation];
        NSTimer *timer;
        timer = [NSTimer scheduledTimerWithTimeInterval:10
                    target:self
                    selector:@selector(CurrentLocationIdentifier)
                    userInfo:nil
                    repeats:NO];
}

Where CurrentLocationIdentifier is a method that requests the start update again.

But it runs the first time, and then don't fire the scheduled task! What am I doing wrong? Should it be done some other way?

Answer 1

If you don't need detailed location updates in the background then the significant location update service is probably the best approach.

- (BOOL)application:(UIApplication *)application
didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
        ... // Any other initialisation you already have
    locationManager = [CLLocationManager new];
    locationManager.delegate = self;
    locationManager.distanceFilter = kCLDistanceFilterNone;
    locationManager.desiredAccuracy = kCLLocationAccuracyBest;
    [locationManager startUpdatingLocation];
}

- (void)applicationDidEnterBackground:(UIApplication *)application
{
    if ([CLLocationManager significantLocationChangeMonitoringAvailable] {
        [locationManager stopUpdatingLocation];
        [locationManager startMonitoringSignificantLocationChanges];
    }
    else {
        //Decide what you want do to if it isn't available
    }
}

- (void)applicationDidEnterForeground:(UIApplication *)application
{
    [locationManager startUpdatingLocation];
    [locationManager stopMonitoringSignificantLocationChanges];
}

By the way, the delegate method you are using, locationManager:didUpdateToLocation:fromLocation: is deprecated and you should use locationManager:didUpdateLocations:

UPDATE Significant location change isn't available on all devices, so I added a check to my code. You need to decide what approach to take on a device where it isn't available - stick with standard updates, perhaps increasing distanceFilter

Answer 2

I have a project on Github, https://github.com/dsdavids/TTLocationHandler , that you are welcome to download and fiddle with. TTLocationHandler is a drop in class that you can set as you wish to get the sort of results others have been pointing to. I made it when I was in exactly your situation, trying to figure out how to use location services in the background.

I would strongly advise that you forget any ideas of trying to fire regularly by any scheduled timer. The idea is to set the handler to fire for events as makes sense then analyze the return and further filter down your response to only as much activity as needed. I find significant location changes to be the best trade off.

You are able to set this for tracking non stop, then respond only as often as you require. You better have a good reason for that battery hit or your app will be rejected. My own app was rejected at first, even though I was setting it to only go full bore if it was plugged in to power. I suppose they were right though. I was able to get everything I need with significant location changes and region monitoring. My app never lets the locationManager go wild and has little impact on battery.

Answer 3

There is no way to wake up the application after a given time interval to execute your code. You really have two options, background fetches, and either region monitoring or significant location changes.

In terms of getting location updates periodically (based on time rather than distance moved), the best you can do is utilize iOS multitasking API performFetchWithCompletionHandler , which in a nutshell allows the OS to wake you up when it determines you can have time to process. You'll have about 30 seconds of wall time to handle what you want to and go back to sleep.

https://developer.apple.com/library/ios/documentation/uikit/reference/uiapplicationdelegate_protocol/index.html#//apple_ref/occ/intfm/UIApplicationDelegate/application:performFetchWithCompletionHandler :

There are a number of steps involved to get this set up, but it's pretty easy and should point you in the right direction. Note that this will not allow you to schedule these events whenever you want, you are really limited by the OS and the algorithm it uses to determine how often you should be allowed to perform background fetches. If you take a long time and use lots of battery, you will get less frequent fetches, and if you take too much time and never complete you'll be terminated. Being "responsible" in the background ends up with the OS giving you more time.

In my experience, being as "responsible" as possible while doing location updates and sending server requests, background fetches occur approx. 15-30 minutes apart.

If you want to be woken up when users move some specified distance, region monitoring is a pretty good (although imperfect) way to handle that, and can allow your app to wake up, start a long running background task (30 seconds) and do what you need to do before ending the task and going back to sleep.