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As we know, the default flow in Android for such scenario is calling the activity's respective onSaveInstanceState, onStop, onDestroy methods before releasing the reference to the Activity object.

However it appears I have a case when my application is on the background, the activity gets killed without those methods being called, but my application itself does not get destroyed.

However I am unable to force-reproduce this. Whenever I use applications on the foreground that require a lot of resources, the whole process gets killed, not just the activity.

Which kind of makes me wonder, because I believe the 'app killing' on low resources is essentially just the old signal way, does the Android system actually 'kill' (release) an activity instantly without calling these methods? Or am I chasing ghosts?

Roberto Lombardini
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George
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  • Is this a one in a thousand type scenario, or is happening regularly ? – IanB Aug 05 '13 at 09:03
  • Can you provide any evidence for this? I am not sure what you mean by "killed". I do not believe that Android will, e.g., release an Activity for GC without first calling its `onDestroy` method. As you note, it can terminate the process that contains the Activity which will have the affect of terminating the Activity, wo/callback. There is also Doze, which might make an Activity quiescent. – G. Blake Meike Jan 07 '18 at 17:16

3 Answers3

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Android app out of memory issues - tried everything and still at a loss

This is not how things work. The only memory management that impacts activity lifecycle is the global memory across all processes, as Android decides that it is running low on memory and so need to kill background processes to get some back

Now the explanation in the official documents is more clear

The system never kills an activity directly to free up memory. Instead, it kills the process in which the activity runs, destroying not only the activity but everything else running in the process, as well. To learn how to preserve and restore your activity's UI state when system-initiated process death occurs, see Saving and restoring activity state.

CharlesYale
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It is possible Android OS kills only some of your activities even if your app is in foreground. For instance if you have two activities A and B, and when A calls startActivity / startActivityForResult to start activity B then Android may deceide to destroy activity A's instance because it is taking up too much memory space.

You can force killing activities which don't run in the foreground by checking Don't keep activities in developer options menu.

maRci002
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Does the Android system actually 'kill' (release) an activity instantly without calling these methods?

Yes it does. Here's what the docs say in regards to onStop():

Note that this method may never be called, in low memory situations where the system does not have enough memory to keep your activity's process running after its onPause() method is called.

and in regards to onDestroy():

There are situations where the system will simply kill the activity's hosting process without calling this method (or any others) in it, so it should not be used to do things that are intended to remain around after the process goes away.

Do not count on this method being called as a place for saving data! For example, if an activity is editing data in a content provider, those edits should be committed in either onPause() or onSaveInstanceState(Bundle), not here.

"However I am unable to force-reproduce this." - you could reproduce this situation by sending your application in background and then using the DDMS to kill the process manually.

Andy Res
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    I want to 'kill'(release) the activity *without* killing the application. I am asking does the Android system kill an activity without calling these methods AND without killing the application? – George Aug 05 '13 at 09:07
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    Sorry then, I misunderstood. I can not say for sure, but while reading the docs I see everywhere is talking about killing the app process, not a particular activity. So I would guess that if one of your activities performs some "heavy" task and is sent to background, then the Android OS will kill the whole application. – Andy Res Aug 05 '13 at 09:14
  • I am hitting the same behaviour as well in my testing - either onStop() and onDestroy() are called and the activity the destroyed or the application gets killed. But I cannot find definitive answer in the docs. – George Aug 05 '13 at 09:20