significantLocationChanges will not work until screen is turned on - ios

Question

I am in the process of testing location updates via the background APIs that relaunch an app. I have successfully tested visits and regions and am using this same app to also test significantLocationChanges (SLC). I run my app, press home twice then swipe it off to kill it. Then I drive around. I can observe the app background activity without touching the phone via a server where (see code below) the singleton method sendBackgroundTestRecord uploads simple status messages to the server.
When I test visits and regions I have no problems. However when I test SLC, nothing happens until I turn the phone's screen on (pressing the power or home button once -- not re-running the app, or even unlocking the phone). I can drive a far distance without anything happening. I suspect the app has received an SLC event sometime during that drive because as soon as I turn the phone on for a about 2 seconds, the code below executes and I can observe the messages on the server.
I believe this is not just a network connectivity delay because the sendBackgrounTestRecord method uses a time stamp. The records on the server show a time stamp of when I turned the screen on, not when the SLC event is suspected to have fired.
I never have this problem with visits or regions, only SLC. By the way, the code has gone through many changes trying to chase this down. The latest attempt (code below) was to put everything in the appDelegate.
Any ideas?
Thanks in advance for any ideas whatsoever!
EDIT: I added beginBackgroundTaskWithExpirationHandler, which was in my original tests too.
// AppDelegate.h
#import <UIKit/UIKit.h>
#import <CoreLocation/CoreLocation.h>
#interface AppDelegate : UIResponder <UIApplicationDelegate, CLLocationManagerDelegate>
#property (strong, nonatomic) UIWindow *window;
#property (strong, nonatomic) CLLocationManager *locationManager;
#end
// AppDelegate.m
#import "AppDelegate.h"
#import "clsCommon.h"
#interface AppDelegate ()
#end
#implementation AppDelegate
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
//Ask iOS for more time to process - before we do anything else
[clsCommon sharedInstance].backgroundTaskID = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{}];
[[clsCommon sharedInstance] sendBackgroundTestRecord:#"didFinishLaunchingWithOptions"];
self.locationManager = [[CLLocationManager alloc] init];
self.locationManager.delegate = self;
if([self.locationManager respondsToSelector:#selector(setAllowsBackgroundLocationUpdates:)]) {
[self.locationManager setAllowsBackgroundLocationUpdates:YES];
}
self.locationManager.desiredAccuracy = kCLLocationAccuracyBestForNavigation;
self.locationManager.distanceFilter = kCLDistanceFilterNone;
self.locationManager.activityType = CLActivityTypeAutomotiveNavigation;
self.locationManager.allowsBackgroundLocationUpdates = YES;
self.locationManager.pausesLocationUpdatesAutomatically = NO;
if([self.locationManager respondsToSelector:#selector(requestAlwaysAuthorization)]) {
[self.locationManager requestAlwaysAuthorization];
}
[self.locationManager startMonitoringSignificantLocationChanges];
return YES;
}
- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations{
[[clsCommon sharedInstance] sendBackgroundTestRecord:#"didUpdateLocations"];
CLLocation * currentLocation = [locations objectAtIndex:0];
if(currentLocation !=nil) {
[[clsCommon sharedInstance] sendBackgroundTestRecord:#"didUpdateLocations curLoc not nill"];
}
}
#end

Answer 1

Well, knowing how aggressively iOS resolves all tradeoffs in favor of battery life I would not be surprised very much. For example, behavior of "breadcrumbs" app (set 100m geofence at your current location, move that geofence to new location on exit event) is very different depending on whether iPhone sleeps all the time in your pocket, or you check lock screen occasionally.
However, running an app very similar to yours while traveling back home yesterday did generate location updates for me.
Distances between SLC readings were in 4 to 14 km range, the smallest time gap between two consequent readings - 14 minutes. The app is very similar to yours, it does not include any networking part, just logging events to a local file (NSLog via stderr redirection). Also, I do not configure properties, which are irrelevant for SLC in location manager, like desiredAccuracy, distanceFIlter, activityType. I suggest you start from barebone app and watch for the improvement, which breaks it.
One thing to check is if your app crashes when handling location updates. If it happens in background you will not notice this unless you run logging or check crash logs via Settings.app.

Answer 2

Put some distance in self.locationManager.distanceFilterand is better for battery change self.locationManager.pausesLocationUpdatesAutomatically=YES;
Start Location Manager in iOS 7 from background task