I'm working on a location tracking application that uses both the standard location service and significant change location service in the background (my app is registered for background location updates in iOS 4+) as applicable. Thanks to this question I have a solid understanding of how significant change comes back from the background state and relaunches from a terminated state. However, I'm still not clear on how the standard location service behaves in these instances. Could anyone break down the exact behavior of the standard location service running in the background?
Specifically:
How does the standard location service behave when you leave it running and the app suspends into the background? From my own testing, I've seen that it will continue waking up to receive callbacks on locationManager:didUpdateToLocation:fromLocation: (I have it send the location out a socket and I can see it on the network). Is there a time or memory limit for this callback to process?
Does the standard location service continue to run even when my app is terminated? That is, will it ever relaunch with application:didFinishLaunchingWithOptions: with UIApplicationLaunchOptionsLocationKey the way the significant change service does? I assume it the CLLocationManager would also need to be restarted in this case, as the significant change service does.
Thanks.
Answer to both 1 & 2, If you have registered your app as using background location then your app does not get terminated and continues to run in the background until you do this:
[locationManager stopUpdatingLocation];
So, there is no time or memory limit however there is a battery limit. If your battery is low, all apps using gps will be closed. Since your app is not terminated in normal circumstances, either it is not required to or it does not relaunch (after being terminated coz of battery) with UIApplicationLaunchOptionsLocationKey
Standard and significant services are different in this manner that significant wakes up the app whenevr there is a location update but standard makes app run continuously and hence drain battery.
Before you choose what service to use consider reading the Location-Awareness Programming guide.
Related
iOS5. I've got a CLLocationManager set up properly, and it listens to region enters / exits.
It all works fine. But when I killed my app, and I entered a region, I received a local notification (which was defined in the didEnterRegion method) AND it started up my application again. Is this standard behaviour or is there something else going on? I thought it would launch the app in the background, perform the didEnterRegion: and kill itself again after a while. All I need to do, is make a HTTP call inside the didEnterRegion:
Anyone who dealt with something similarly?
This is expected behavior.
When your application is not running but the geofence border crossing is registered for your app, it will be started and the callback triggered.
It will not be killed after that, unless the system decides, it needs the memory.
Don't worry about it, your application will be dormant even if it has been started, so there is no speed/battery/etc penalty.
see docs:
Handling Boundary-Crossing Events for a Region
Every time the user’s current location crosses a boundary region, the
system generates an appropriate region event for your app. If your app
is already running, these events go directly to the delegates of any
current location manager objects. If your app is not running, the
system launches it in the background so that it can respond. Apps can
implement the following methods to handle boundary crossings:
I have to develop a kind of GPS navigation application that needs to constantly keep track of the position of the user, which is moving by car.
In the specific, I don't have to display the current location on a map but just to record its position with the best possible precision in order to calculate the total distance traveled.
Of course the application needs to continue its work in background if the user switch to another app, a phone call come in or something like that…
From the tests I have made and from what I have learned from this useful post (and from the documentation), it seems to me that the best choice in this case is the Standard location service, with the application configured with the UIBackgroundModes = location in the .plist file.
In this way it will continue to receive the location updates even if in background and it will never be suspended by the OS (this is actually true only if [locationManager startUpdatingLocation] has been called). This is also confirmed by this guys.
I have personally verified that is true simply by running the app with Instruments and the Memory monitor module where you can see the various flags about the app states, putting the app in background first with UIBackgroundModes set to location and startUpdatingLocation active, and after without it.
1) I'm now wondering what to do when the app is terminated when it is tracking the position. I don't want to loose any location updates so I need to wake up it again whenever a new update is available.
The documentation say:
Important: The applicationWillTerminate: method is not called if your
app is currently suspended.
But because in my case it will be never suspended (it will stay in background but not suspended), my logical conclusion is that applicationWillTerminate will be always called and so I could register for a Significant location update or Region monitoring inside of this method in order to be waked up and then restart the Standard location service.
Is applicationWillTerminate the right place to put this code?
2) An application working in background but not suspended could be terminated by the OS for no other reasons than a very low memory condition or for my app don't properly respond to a memory warning? (the user could also manually close it). I was concerned if applicationWillTerminate wouldn't be called in some way.
3) Could Apple not approve an app which constantly use the standard location services in background because of its quick battery drain?
Have you ever had approve problems for similar apps?
since you are asking many questions which you shoukd not do here, i cam give you only aswrs to a part of it.
if the app is terminated, then you cannot restart it anymore.
This is usually the case when the user terminates the app.
Dont worry Apple ( ios) will not terminate your app. your app will not use much memory, games with huge bitmap graphics are more likely to be termin.
evry gps app will drain the bat. that is not a reason for not aproving.
suspended means that app is not in background mode, it is sleeping. you will not receive Gps, so there is no need to call you on terminate. you have to save data before, see the apple docu on background modes and app life cycle.
My question is: Is CLLocationManager continue running, while my app is inactive?
Yes, if CLLocationManager is first called startUpdatingLocation method, and in the AppName-Info.plist file is added Required Background Modes -> App registers for location updates
Yes, it could. You have two options for handling location service events when your app is suspended, which can be read at the article: Getting the User’s Current Location.
As noted:
There are two different services you can use to get the user’s current location:
The standard location service is a configurable, general-purpose solution and is supported in all versions of iOS.
The significant-change location service offers a low-power location service for devices with cellular radios. This service is available only in iOS 4.0 and later and can also wake up an application that is suspended or not running.
Also, as noted at the bottom of this article in the section "Getting Location Events in the Background":
If your application needs location updates delivered whether the application is in the foreground or background, there are multiple options for doing so. The preferred option is to use the significant location change service to wake your application at appropriate times to handle new events. However, if your application needs to use the standard location service, you can declare your application as needing background location services.
An application should request background location services only if the absence of those services would impair its ability to operate. In addition, any application that requests background location services should use those services to provide a tangible benefit to the user. For example, a turn-by-turn navigation application would be a likely candidate for background location services because of its need to track the user’s position and report when it is time to make the next turn.
There are some important subtleties with this (as of iOS 7.1):
The Location Update background mode should NOT be used if you are just looking for significant change and region enter/exit events. You will still receive these events even if the background flag is NOT set, and you will save a lot of battery at the same time.
If you do the above, you need to be mindful of limited permitted background time. If you don't take care to wrap up network requests etc. in the permitted time, you will network transaction failures.
You should ONLY use the location background mode if you need to use detailed location tracking (e.g. -startUpdatingLocation), in which case this background mode will keep your app awake.
Using the location background mode when not getting detailed location will piss off your users and may get your app rejected during the review process (depending on how you use location throughout your app).
Your app may be killed at anytime by the OS if you do not have the background location mode set, so you will need to be sure to properly re-initialize your CLLocationManager instance in applicationDidFinishLaunching or applicationWillFinishLaunching in order to get the subsequent updateLocation or didEnter/ExitRegion delegate call. Just because location wakes up your app with a location update, it does NOT magically re-create your CLLocationManager without you programming it!
Hope that helps!
To disable CLLocationManager while the app is in backround mode you simply must not add the
"App registers for location updates"
in the
"Required background modes"
key of the info.plist file.
I suggest to use the significant-change location service instead of the standard location service whenever possible, to preserve device battery.
Applications can register for significant location changes.
(Recommended) The significant-change location service offers a
low-power way to receive location data and is highly recommended for
applications that do not need high-precision location data. With this
service, location updates are generated only when the user’s location
changes significantly; thus, it is ideal for social applications or
applications that provide the user with noncritical, location-relevant
information. If the application is suspended when an update occurs,
the system wakes it up in the background to handle the update. If the
application starts this service and is then terminated, the system
relaunches the application automatically when a new location becomes
available. This service is available in iOS 4 and later, only on
devices that contain a cellular radio.
From https://developer.apple.com/library/archive/documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/BackgroundExecution/BackgroundExecution.html
An app can be relaunched when the location changes. However, can it be started automatically when the phone is started? The documentation isn't quite clear.
The service will start when the user launches your application, and terminate if it is closed. The service will remain running if the application is running in the background.
Developers cannot integrate services into the OS, for security purposes.
No, you cannot have your application run automatically when the phone is started. In addition, if the user starts your application manually and puts it into the background, the system may eventually kill it when it needs the memory.
"Including the voip value in the UIBackgroundModes key lets the system know that it should allow the app to run in the background as needed to manage its network sockets. An app with this key is also relaunched in the background immediately after system boot to ensure that the VoIP services are always available."
check iOS docs here
Although if you do this for an illegitimate reason I am guessing your app will either not get approval or get booted quickly.
I am writing an application that records a users position at regular intervals whilst walking. I am using an NSTimers to schedule "startUpdatingLocation" followed by calling "stopUpdatingLocation" shortly afterwards to save as much battery as possible.
I want the user to be able to start the application and lock the phone thereby putting the application in an inactive state. My question is when this happens my application (when running via Xcode) seems to continue as normal, but I am curious if there are any differences in the way the application runs in this state as apposed to when the application is running as active?
From the docs it only mentions "applicationWillResignActive" with regards to the application passing through that state on its way to the background. I am more interested in how an application behaves when a used locks the UI and puts the phone away, I just want to make sure its going to keep doing what it should be doing or do I need to take extra measures?
When you app hits applicationWillResignActive it can continue to receive location updates if you use the UIBackgroundModes option in your apps info.plist.
Add the location key.
It is important that you do not use a timer in the background as timers will run but hold their "fire" until the app becomes active again. Thus you will only get one read when the user comes back to the app. The GPS location accuracy level is what will drive how much the battery is affected.
In your app description in the App Store, Apples requires:
Continued use of GPS running in the
background can dramatically decrease
battery life.
You app will not be allowed to go live until the above text is in the description for the user to read.
You should definitely be testing this on a device. The simulator doesn't auto-lock, for instance.
applicationWillResignActive is called when the user presses the home button, when another app fires a notification the user accepts (including when a call comes in), and when the device locks.
Look into the multitasking documentation, and what it has to say about background location updates.
My suggestion is that you conserve the user's battery by:
- starting a timer, which when fired, starts location updates (and stops the timer)
- when you get an adequately-accurate position record, stop location updates and restart the timer
- if location updates fail, restart the timer for a longer period. Maybe they're underground.
The most efficient approach is using significant location update service while your application is in the background or the screen is locked on your app. You might get one update every ten minutes or so.
Remember also, the user can disable your app's location services permissions. Especially these days...