后台位置服务在iOS 7中不起作用

Question

I've recently upgraded my iOS devices to use iOS 7. One of the apps that we're developing uses background location services to track device location and all of our testers have reported that the app no longer appears to track in the background under iOS 7.

We have verified that backgrounding for the app is enabled in the settings on the device and the previous build worked flawlessly under iOS 6. Even if the device were cycled, the app would restart after a location update.

Is there something else that needs to be done to make this work under iOS 7?

Answer 1

Here is the solution that I used to get continuous location from iOS 7 devices no matter it is in foreground or background.

You may find the full solution and explanation from blog and also github:-

1. Background Location Update Programming for iOS 7 and 8

2. Github Project: Background Location Update Programming for iOS 7 and 8

Methods and Explanation:-

1. I restart the location manager every 1 minute in function didUpdateLocations

2. I allow the location manager to get the locations from the device for 10 seconds before shut it down (to save battery).

Partial Code Below:-

-(void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations{

for(int i=0;i<locations.count;i++){
    CLLocation * newLocation = [locations objectAtIndex:i];
    CLLocationCoordinate2D theLocation = newLocation.coordinate;
    CLLocationAccuracy theAccuracy = newLocation.horizontalAccuracy;
    NSTimeInterval locationAge = -[newLocation.timestamp timeIntervalSinceNow];

    if (locationAge > 30.0)
        continue;

    //Select only valid location and also location with good accuracy
    if(newLocation!=nil&&theAccuracy>0
       &&theAccuracy<2000
       &&(!(theLocation.latitude==0.0&&theLocation.longitude==0.0))){
        self.myLastLocation = theLocation;
        self.myLastLocationAccuracy= theAccuracy;
        NSMutableDictionary * dict = [[NSMutableDictionary alloc]init];
        [dict setObject:[NSNumber numberWithFloat:theLocation.latitude] forKey:@"latitude"];
        [dict setObject:[NSNumber numberWithFloat:theLocation.longitude] forKey:@"longitude"];
        [dict setObject:[NSNumber numberWithFloat:theAccuracy] forKey:@"theAccuracy"];
        //Add the vallid location with good accuracy into an array
        //Every 1 minute, I will select the best location based on accuracy and send to server
        [self.shareModel.myLocationArray addObject:dict];
    }
}

//If the timer still valid, return it (Will not run the code below)
if (self.shareModel.timer)
    return;

self.shareModel.bgTask = [BackgroundTaskManager sharedBackgroundTaskManager];
[self.shareModel.bgTask beginNewBackgroundTask];

//Restart the locationMaanger after 1 minute
self.shareModel.timer = [NSTimer scheduledTimerWithTimeInterval:60 target:self
                                                       selector:@selector(restartLocationUpdates)
                                                       userInfo:nil
                                                        repeats:NO];

//Will only stop the locationManager after 10 seconds, so that we can get some accurate locations
//The location manager will only operate for 10 seconds to save battery
NSTimer * delay10Seconds;
delay10Seconds = [NSTimer scheduledTimerWithTimeInterval:10 target:self
                                                selector:@selector(stopLocationDelayBy10Seconds)
                                                userInfo:nil
                                                 repeats:NO];
 }

Update on May 2014 : I got a few requests for adding sample codes on sending the location to server for a certain time interval. I have added the sample codes and also combined a fix for BackgroundTaskManager to solve a glitch for background running over an extended period of time. If you have any questions, you are welcomed to join us for a discussion here: Background Location Update Programming for iOS 7 with Location Update to Server Discussion

Update on January 2015 : If you want to get the location update even when the app is suspended, please see: Get Location Updates for iOS App Even when Suspended

Answer 2

If you look at WWDC 2013 Session video #204 - What's new with multitasking pdf, page number 15 clearly mentions that apps wont launch in the background if user kills it from the app switcher. Please see the image,

Answer 3

I think they made an optimization (probably using motion sensors), to detect "relatively" stationary positioning of the phone and they stop the location updates. This is only a speculation, but my tests currently show:

1. Starting location updates; (tested with accuracy of 10 and 100 meters, 3 times each)
2. Turn device's screen off to put the app in the background;
3. Leave the device stationary (eg on a desk) for 30 min.

The data I log shows the geo-updates stop coming after ~ 15m and 30s. With that all other background processing you do is also terminated.

My device is iPhone 5 with iOS 7.

I am 95% sure, this wasn't the case on iOS 6/6.1. Where getting geo updates with 100m accuracy used to give you pretty much continuous running in background.

Update

If you restart the location manager every 8 minutes, it should run continuously.

Update #2

I haven't tested this in latest, but this is how I restarted it when I wrote the post. I hope this is helpful.

- (void)tryRestartLocationManager
{
    NSTimeInterval now = [[NSDate date] timeIntervalSince1970];

    int seconds = round(floor(now - locationManagerStartTimestamp));

    if ( seconds > (60 * 8) ) {
        [locationManager stopUpdatingLocation];
        [locationManager startUpdatingLocation];
        locationManagerStartTimestamp = now;
    }
}

Answer 4

One of my iOS app needs to send location update to server at regular intervals and following approach worked for us....

Starting in iOS 7:

• an app must have already been using location services (startUpdatingLocation) BEFORE having been backgrounded in order for the eligible for background run time
• the background grace period timeout was reduced from 10 minutes to 3 minutes
• stopping location updates (via stopUpdatingLocation) will start the 3 minute backgroundTimeRemaining count down
• starting location updates while already in the background will not reset the backgroundTimeRemaining

So, DO NOT STOP the location updates anytime...Instead, prefer to use the necessary accuracy (fine location vs coarse location). Coarse location does not consume much battery...so this solution solves your problem.

After much searching online, found a link which provide a viable solution for iOS 7. The solution is as follows:

• While the app is still in the foreground, start location updates (startUpdatingLocation) but set the accuracy and distance filters to very course-grained (eg 3 km) updates. It is important to do this in the foreground (in applicationDidEnterBackground is too late).
• When a fine-grained resolution is required, temporarily set the accuracy and distance filters to get the best possible location, and then revert them back to the course-grained values – but never stop location updates.
• Because location updates are always enabled, the app will not get suspended when it goes to the background.

And make sure you add the following to your application's Info.plist “location” to the UIBackgroundModes key “location-services” and “gps” to the UIRequiredDeviceCapabilities key

Credits: http://gooddevbaddev.wordpress.com/2013/10/22/ios-7-running-location-based-apps-in-the-background/

Answer 5

I found another thread Start Location Manager in iOS 7 from background task Sash mentioned that

I found the problem/solution. When it is time to start location service and stop background task, background task should be stopped with a delay (I set 1 second). Otherwise location service wont start.

Can anyone try that and verify?

Nikolay, can you paste your code here? I tried to restart the location manager every 8 minutes but it does not run continuously.

Update:

After searching High and Low, I found the Solution from Apple Forum!

In iOS 7, you can not start the location service in background . If you want the location service to keep running in the background, you have to start it in foreground and it will continue to run in the background.

If you were like me, stop the location service and use timer to re-start it in the background, it will NOT work.

For more detailed information, you can watch the first 8 minutes of video 307 from WWDC 2013: https://developer.apple.com/wwdc/videos/

Feb 2014 Update: I can get the location continuously from device using iOS 7 after several months of trying. You may see the full answer here: Background Location Services not working in iOS 7

Answer 6

Is the icon on the status bar turned on? It's a strange behaviour I had too. Check my question: startMonitoringSignificantLocationChanges but after some time didUpdateLocations is not called anymore

I discovered that the significant location changes was on but simply stopping and restarting the service (for significant changes) was not firing new locations.

Answer 7

必须将CLLocationManager类的pausesLocationUpdatesAutomatically属性设置为false才能禁止系统暂停位置更新。