IssueTracker

Component used: Fragment

Version used: 1.3.0-rc01

Devices/Android versions reproduced on: Samsuns S10e/Android 10, Google Pixel 4XL/Android 11

Reproducing: Attached a sample app, look at MainActivity/MainActivityViewModel/FirstFragment.

Description of the issue:

I have stumbled upon a Fragment lifecycle issue where under certain conditions the Fragment#onResume() method does not get called. Conditions of reproducing:

1. Using AndroidX Fragment 1.3.0-rc01 (initially reproduced on 1.3.0-beta02, verified it is NOT fixed with the later release),
2. Using an enter transition in a Fragment transaction (ChangeBounds in my example),
3. Performing a Fragment transaction from Activity#onCreate() as a result of a LiveData emission.

It feels like some race condition, but is surprisingly stable at reproducing (pretty much at 100%, I only failed to reproduce it once on a fresh install) at different devices.

In the logs:

2021-01-10 15:05:29.242 21379-21379/com.example.fragmentnoresume I/DEBUG123: FirstFragment#onViewCreated
2021-01-10 15:05:29.250 21379-21379/com.example.fragmentnoresume I/DEBUG123: MainActivity#onResume

Any of the following actions fix the issue:

• Removing the enter transition for the Fragment,
• Switching to direct invocation or StateFlow instead of LiveData in Activity (for initiating a Fragment transaction),
• Inserting a delay of 100+ms before starting the Fragment transaction:

private fun showFirstScreen() {
    val fragment = FirstFragment().apply {
        enterTransition = Fade()
    }

    lifecycleScope.launch {
        delay(100)
        supportFragmentManager.beginTransaction()
            .add(R.id.fragment_container, fragment, fragment.javaClass.name)
            .commitAllowingStateLoss()
    }
}

Once one of these workarounds has been applied, logs are like this:

2021-01-10 15:10:14.494 25298-25298/com.example.fragmentnoresume I/DEBUG123: MainActivity#onResume
2021-01-10 15:10:14.616 25298-25298/com.example.fragmentnoresume I/DEBUG123: FirstFragment#onViewCreated
2021-01-10 15:10:14.932 25298-25298/com.example.fragmentnoresume I/DEBUG123: FirstFragment#onResume

or

2021-01-10 15:13:03.312 25695-25695/com.example.fragmentnoresume I/DEBUG123: FirstFragment#onViewCreated
2021-01-10 15:13:03.316 25695-25695/com.example.fragmentnoresume I/DEBUG123: MainActivity#onResume
2021-01-10 15:13:03.316 25695-25695/com.example.fragmentnoresume I/DEBUG123: FirstFragment#onResume