In the flow diagram for an Android app activity lifecycle (shown below) there is a route by which the 'App process' is killed and onDestroy() is not called. It seems this is most commonly done to free up memory resources for a different activity.
All that is fine, but how do I test this scenario? Either on device or in the simulator.
If you force stop your app, all BroadcastReceivers and also app widgets, which extend BroadcastReceiver, will stop working. See also this SO post by Commonsware
So force stopping the app is not ideal for testing app behavior under low memory conditions. What else can you do?
One option: write your own task killer app and use ActivityManager.killBackgroundProcesses(). As the documentation says:
This is the same as the kernel killing those processes to reclaim memory
Another option: manipulate the device settings as explained by Xavi Gil in his answer to Simulate low battery & low memory in Android
Steps:
Navigate to your app
Press home button so the app will not get the onDestroy call
Go to system settings and find the right place to "force close" your app
Navigate back to your app
Important note: DO NOT use back button when leaving your app when you are going to system settings, use home button instead so the app does not get killed.
The easiest and most clean solution to test those life cycle is to enable the "Don't Keep Activities" settings in the developer settings on your device.
This way you even get your activity killed as soon as you start a new activity. So if you press back than the old activity will be recreated.
I didn't use any services in my application and closing the application by using
this.finish();
but my application still not stopped properly and it is running in background.when i go to application settings the force stop button is still enabled.
kindly share your views on proper exit of android application.
It's quite possible you have another activity around.
From the Android docs, see Activity.finish():
Call this when your activity is done and should be closed. The
ActivityResult is propagated back to whoever launched you via
onActivityResult().
There's no promise made that the activity will be closed right away on calling finish(), only that this is something that should be done. Usually this does happen right away, but without seeing your project I cannot comment further.
Note that Android, unlike iOS, doesn't really have a well-defined notion of an app. "Apps" can share activities and so on. For example it's not hard, but it's also non-trivial, for an "app" to know that it will go to background or that it has resumed.
I have written a simple database program in android. It runs fine, there is no force close error. But I checked from my application from Settings App I see the Force Close option enabled, which implies that my application is still running in the background, even though I have completely came out from my application to the home screen by pressing back key. And moreover I am not using any services, alarm or broadcast things.
Can some one please guide me what may be the probable reason?. Or is it okay? Or will it crash if I put it on device?
Can some one please guide me what may be the probable reason?. Or is it okay? Or will it crash if I put it on device?
Your application is alive until Android OS needs more memory and destroys it. What I have understood does Android start destroying activities before killing the whole application. This means that your application can be alive even if you have finished your activities.
Do not worry about this; Android OS is handling this extremely well.
I am basically looking for the same functionality found in the DevTools (Development.apk) app that comes with the emulator. I am wanting to perform similar testing on an actual device but the DevTools app does not work properly on the device I have so I cannot use it.
I am looking to test in a similar way.
What this does is causes each Activity to be destroyed whenever it leaves the screen, holding onto its instance state just as if the system needed resources and had killed it. (So I can't just call finish)
Is there a way to do this?
Thanks
You can kill your app's process at any time using the DDMS stop button. highlight your application in the list and click the stop sign button. your application will be destroyed like it was killed by the system.
See the stop button in the left pane(Devices) above each device listing:
Android doc say:
"When the system, rather than the user, shuts down an activity to conserve memory, ... "
But how to simulate this situation?I want to debug the onRestoreInstanceState(Bundle) method,but don't know how to.
You can't do it in an automated way b/c its completely non deterministic.
See my answer here: https://stackoverflow.com/a/15048112/909956 for details.
But good news is that all you need to do is just simulate calling onSaveInstanceState and you are indirectly testing this low memory situation.
onSaveInstanceState can be triggered by:
losing focus (by pressing home which in essence is like switching from your app to launcher app), launching another activity, pressing recents
changing orientation. this is the easier way if you are using an emulator
changing developer setting: goto developer options --> Apps --> Don't keep activities. This is best option if you are testing temporarily on an actual device.
I've used the "Don't keep activities" developer option to reproduce a crash that happened when an activity was killed due to memory pressure. You can find it in the Apps section of Settings->Developer Options.
It destroys every activity as soon as you leave it. E.g. if you press home to put your app in the background the current activity is destroyed. See https://stackoverflow.com/a/22402360/2833126 for more information.
There's two way to simulate the android killing process: using the setting "Don't keep activities" in developer settings or killing the app process by yourself.
To kill the process, open the activity you want to test, then press home button to send your app to background, and then, using the DDMS in Android Studio (Android Device Monitor), select the process and then stop the process (as seen in the image below). Your app was killed. Now, open your app again (accessing the list of open apps). Now you can test the killed state.
For the purposes of debugging onRestoreInstanceState(), just change the screen orientation ([Ctrl]-[F11] in the emulator). Your activity will be destroyed and recreated, and the onSaveInstanceState()/onRestoreInstanceState() pair will be invoked.
Use the SetAlwaysFinish app (works on a real device and in the emulator) or use the Google DevTools app (works in the emulator only).
These apps use the hidden AlwaysFinish setting of the ActivityManagerNative class to change the behavior of the OS and cause it to immediate unload every activity as soon as it's no longer in the foreground. This will reliably trigger the onSaveInstanceState and onRestoreInstanceState events.
See link below for more details:
http://bricolsoftconsulting.com/how-to-test-onsaveinstancestate-and-onrestoreinstancestate-on-a-real-device/
To debug onRestoreInstanceState you could do the following:
make sure you can debug application right after its start (calling android.os.Debug.waitForDebugger() from your constructor helps, it hangs your application until debugger is connected),
put you application in some state,
causally kill it from Settings->Apps,
causally switch back to it through Recent Apps button (it will still be in the list),
at this moment your application will be started anew and onRestoreInstanceState will be immediately called on the top activity.
Good answers here.
Now, residing in the distant future, using Instant Run in Android Studio will also trigger a save and restore when activities are restarted with code changes.
There's a decent solution for this in Android 6 and newer. See my answer here: Simulate killing of activity in emulator