Android Architecture Cannot add the same observer with different lifecycles

Question

I have application that has MainActivity, that starts InvoiceActivity and that starts InvoicePaymentActivity which finally starts PaymentSuccessActivity.

I started using architecture components and it seems to work fine, bud I have found problem when starting MainActivity from PaymentSuccessActivity.

Up until now, I would just start new Intent and the app would "reset" to main screen. With ViewModel I am getting "Cannot add the same observer with different lifecycles".

I have found 2 solutions, but cannot think which one is better:

Subscribe to observer in onResume, unsubscribe onPause
Finish all previous activities except MainActivity after the next one is started. So when I just finish PaymentSuccessActivity, user will be on MainActivity. This has a drawback of user navigating backwards...

But it seems I cannot add the observer again... how can I unsibscribe/subscribe? My code does not work right now...

override fun onResume() {
    super.onResume()
    viewModel.intercom.observe(this, observer)  
}


override fun onPause() {
    super.onPause()
    viewModel.intercom.removeObserver { observer }
}

But why are you adding **the same** observer? Why won't you create a new one? — azizbekian, Apr 26 '18 at 14:14
I will try, but I was doing it simple like this so I can have a reference for removing observer. — kvgr, Apr 26 '18 at 14:21

score 1 · Answer 1 · answered Apr 26 '18 at 14:33

1

So this whole problem was base on using anonymous Observer class. Once I created my observer class implementing observer interface, the app startet to work fine, without needing to manually observer/remove. Can anyone explain why this is issue?

answered Apr 26 '18 at 14:33

kvgr

325
4
17

I came up with this issue today and it looks like the problem comes from JVM object reuse. I had simple anonymous class observer that only logged the value and I was crashing when moving between fragments. As soon as I added fragments field to the log problem disappeared since my observer was no longer "stateless" (it was capturing its host fragment). See [When does JVM decide to reuse old lambda?](https://stackoverflow.com/questions/29674645/when-does-jvm-decide-to-reuse-old-lambda). – Pawel Oct 30 '20 at 21:00

Android Architecture Cannot add the same observer with different lifecycles

1 Answers1