IssueTracker

Component used: Navigation
Version used: 2.0.0
Devices/Android versions reproduced on: Android 8.1 on Zebra TC51 and TC52

==== MainActivity ====

override fun onCreate(savedInstanceState: Bundle?) {
    val host = supportFragmentManager.findFragmentById(R.id.navigation_host_fragment)
    val fragmentManager = host?.childFragmentManager

    fragmentManager?.addOnBackStackChangedListener {
        handleCurrentFragment()
    }

    handleCurrentFragment()
}

private fun handleCurrentFragment() {
        val host = supportFragmentManager.findFragmentById(R.id.navigation_host_fragment)
        val fragment = host?.childFragmentManager?.primaryNavigationFragment // This is null in the second case mentioned below
        val enableRead = fragment is BarcodeListener && fragment.isScanningEnabled()
        scanner.setScanningEnabled(enabled = enableRead)

        scannerIndicatorCard.visibility = if (fragment is BarcodeListener) View.VISIBLE else View.GONE
}

=== Actions that work ====
- Start on <Fragment A>.
- Navigate from <Fragment A> to <Fragment B> using directions.
    handleCurrentFragment() is called, primaryNavigationFragment is <Fragment B>
- Navigate from <Fragment B> to <Fragment C> using directions.
    handleCurrentFragment() is called, primaryNavigationFragment is <Fragment C>
- Call navigateUp() from <Fragment C>
    handleCurrentFragment() is called, primaryNavigationFragment is <Fragment B>


=== Actions that cause the issue ===
- Start on <Fragment A>.
- Navigate from <Fragment A> to <Fragment B> using directions.
    handleCurrentFragment() is called, primaryNavigationFragment is <Fragment B>
- Navigate from <Fragment B> to <Fragment C> using directions.
    handleCurrentFragment() is called, primaryNavigationFragment is <Fragment C>
- Navigate from <Fragment C> to <Fragment C> using directions (single top chosen in graph xml)
    handleCurrentFragment() is called, primaryNavigationFragment is <Fragment C>
- Call navigateUp() from <Fragment C>
    handleCurrentFragment() is called, primaryNavigationFragment is null



Attached are screenshots of a graph that would reproduce the issue and the graph discovered on.