Android lifecycle library: Cannot add the same observer with different lifecycles

Question

I have an app I'm working on that's using the lifecycle library but I'm getting an IllegalArgumentException that says "Cannot add the same observer with different lifecycles" I only add observers in onCreate which I thought would be safe. Most of my observers are added via anonymous classes which I assume can't be the issue here since the observer is never recycled. One is using this:

private GpsState gpsState;

void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    getLifecycle().addObserver(gpsState);
    gpsState.observe(this, (state) -> {
        // ...
    });
}

In this example GpsState extends LiveData to provide the current state of the GPS and implements LifecycleObserver to be able to refresh certain values when reaching an ON_RESUME state.

Any idea what I might be doing wrong?

Nokuap · Accepted Answer · 2019-02-28T09:40:49.497

86

In my case the problem was at lambda method of observer is empty. I just tried to add something to it and problem was solved. For example:

gpsState.observe(this, (state) -> {
                Log.d(this.getClass().getSimpleName(), BaseNavigationActivity.this.toString());

});

Most likely that JVM define anonymous classes that use only static references and for such cases it become kinda singleton, so you will have same instance all the time you reference such class.

edited Feb 28 '19 at 09:40

answered Nov 13 '17 at 12:58

Nokuap

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20

Very close, it wasn't empty but it was only accessing static objects which I guess made the compiler reuse the same instance. – TheHebrewHammer Dec 08 '17 at 19:47
If you use Timber: `Timber.i(this.getClass().getSimpleName());` I was just using `Timber.i("...");` and it wasn't enough. – GuilhE Dec 07 '18 at 16:57
2

Yeah, seems you have to add some dynamic thing to it – Nokuap Dec 10 '18 at 07:48
It worked for me too. But can you explain why this works? – gbruscatto Feb 17 '19 at 23:28
No. It's not working in fragment – AlexS Aug 15 '23 at 13:31

score 38 · Answer 2 · answered Mar 01 '19 at 07:27

38

As thehebrewhammer said in a comment, I had the same issue because of Kotlin SAM-Lambda optimization.

viewModel.myLiveData.observe(this, Observer {
    NavigationBackEvent().post()
})

This SAM-Lambda doesn't access anything of the class and will be compiled to a singleton for optimization.
I changed it to a class initialization for forcing new instance at each run:

viewModel.myLiveData.observe(this, MyObserver())

and

class MyObserver : Observer<MyType?> {
    override fun onChanged(it: MyType?) {
        NavigationBackEvent().post()
    }
}

answered Mar 01 '19 at 07:27

Kevin Robatel

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Thanks for the answer. Why lots of examples which uses `this, Observer {...}` works? For example https://github.com/googlesamples/android-sunflower/blob/master/app/src/main/java/com/google/samples/apps/sunflower/GardenFragment.kt – Vasily Kabunov Mar 14 '19 at 04:54
3

@VasilyKabunov It's all related to the fact that if you don't access field of the "parent class". If you access one, the compiler make a `inner class`. If you don't access, no need to instance multiple time, it's always the same. The compiler will optimize it and make a singleton. – Kevin Robatel Mar 14 '19 at 07:24
1

your a life saver ..saved me countless hours. – j2emanue Oct 07 '22 at 12:08

score 6 · Answer 3 · edited Jan 20 '20 at 17:47

6

I had the same issue, these lines of code solved it:

sharedViewModel.getFriendsList().observe(this, object: Observer<ArrayList<User>> {
    override fun onChanged(t: ArrayList<User>?) {
        CurrentUser.friendsList = t
    }
})

edited Jan 20 '20 at 17:47

machnic

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answered Jan 20 '20 at 15:35

Gilad Raz

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score 4 · Answer 4 · answered Dec 01 '19 at 17:39

Based on previous responses all you need to do is create a new Object every time you subscribe your observer.

gpsState.observe(this, object: Observer<GpsState> {
    // ...
});

PD: I assumed that GpsState is the data type you want observe. In my case was Long

Android lifecycle library: Cannot add the same observer with different lifecycles

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