When to call [clLocationManager stopUpdatingLocation] - ios

Question

To save power in my app I have decided to use a mix of startUpdatingLocation when the app is active and go into startMonitoringSignificantLocationChanges mode when the app is in the background. Basically I do the following when the app goes into the background:
-(void)applicationDidEnterBackground:(UIApplication *)application{
[myLocationManager startMonitoringSignificantLocationChanges];
}
And when the app comes back into the foreground I do the following:
-(void)applicationDidBecomeActive:(UIApplication *)application{
//Other irrelevant code
[myLocationManager stopMonitoringSignificantLocationChanges];
[myLocationManager startUpdatingLocation];
}
This seems logical, to me anyways. My question is, should I be calling the stopUpdatingLocation method in the applicationDidEnterBackground event? Like so:
-(void)applicationDidEnterBackground:(UIApplication *)application{
[myLocationManager stopUpdatingLocation];
[myLocationManager startMonitoringSignificantLocationChanges];
}
Where exactly should I be calling the stopUpdatingLocation method?? Please tell me if there is more than one place where this should be done. I'm assuming any error event should stop the updating?

Answer 1

I don't see anything wrong with what you are doing. Note that I have a commercial app that heavily uses location services, and I'm in the midst of rewriting it to improve it's performance and minimize battery usage.
My released version uses sigLocationChanges predominantly (in background & foreground), but switches to using startUpdatingLocation when unhappy with the quality of the location sigLocationChanges gives me, since my UI has to display the users location roughly accurately. I call stopUpdatingLocation immediately after each event to minimize battery drain. In my shipping version this seems to work okay, but my log files have found a tiny subset of users who seem to constantly get poor locations and I'm spinning up the GPS hardware more than I like.
Also in Privacy Settings, the type of location icon displayed for your app will be determined by when you last used the full GPS location mode. Mine always shows the location icon that indicates a heavy battery impact, even if I'm only using startUpdatingLocation briefly a couple times per day, which can make my users paranoid about how my app affects their battery life.
In my new release, to minimize the battery drain of using of startUpdatingLocation, I've cut it's use back to hopefully nil. When the app activates, I now get the current location directly from the location manager, cLLocMgr.location. Typically that's an accurate location, and my UI can be instantly drawn (or refreshed) correctly. I also check it again when certain views are activated to ensure if the user is moving while keeping my app open the display keeps up. Now I only spin up the GPS hardware if the phone has a bad location in a specific situation where a good location is absolutely required in the app. In that case, I limit it's use to 2 minutes (I'm assuming 2 minutes is long enough to get best location from GPS hardware), and wait at least 10 minutes before allowing it's use again.
Your question doesn't give me enough info to tell how accurate you need to be and how dynamic your location display is. But unless you need super accuracy and dynamic display, you should consider just using the current location without spinning up the GPS hardware to save battery.
Edit: Here is the actual code I used for Jeraldo, cleaned up a bit. Note it's been a year since I touched it, so I'm a little rusty on it, hope I didn't clean up anything.
// Called at start to ask user to authorize location data access.
- (void) requestIOSLocationMonitoring {
#if TARGET_IPHONE_SIMULATOR
// If running in siumaltor turn on continuous updating (GPS mode)
// This is for testing as significant change isn't useful in simulator
// Set a movement threshold for new events. This is only used by continiuous mode, not sig change events
// Keep it as low as possible,but not so low as to generate spurious movements.
cLLocMgr.distanceFilter = 30;
// Use continuous location events in simulator.
// desired accuracy only works in continuious (high power) mode.
cLLocMgr.desiredAccuracy = kCLLocationAccuracyBest;
[cLLocMgr startUpdatingLocation];
#else
// If not in simulator app's default is significant change monitoring
[cLLocMgr startMonitoringSignificantLocationChanges];
#endif //TARGET_IPHONE_SIMULATOR
}
// Toggle back and forth between continius updates (GPS on) and
// significant change monitoring
- (void) setGPSMode: (bool) useGPSMode {
// Keep track of time since we last changed GPS mode
NSTimeInterval secsInThisMode = [[NSDate date] timeIntervalSinceDate: lastModeChange];
// inGPSMode is an object instance variable app uses to track mode it is in.
if (inGPSMode != useGPSMode) {
lastModeChange = [NSDate date];
if (!useGPSMode) {
// Tell app to operate as if continuous updating is off
inGPSMode = false;
#if TARGET_IPHONE_SIMULATOR
// But keep using continuous location events in simulator for testing.
cLLocMgr.distanceFilter = 30;
#else
// Turn off continious updates for app on actual devices
[cLLocMgr stopUpdatingLocation];
#endif
} else if (secsInThisMode > cMinGPSModeBreak) {
// Only turn on continuous updating again if it's been off long enough
// Prevents GPS mode from running continiously and killing battery life
inGPSMode = true;
cLLocMgr.desiredAccuracy = kCLLocationAccuracyBest;
cLLocMgr.distanceFilter = kCLDistanceFilterNone;
[cLLocMgr startUpdatingLocation];
}
}
}