IssueTracker

Project: platform/frameworks/support
Branch: androidx-master-dev

commit 85c1de7395f07e3256a50706d4f619e654624250
Author: Ian Lake <ilake@google.com>
Date:   Fri Apr 19 13:54:21 2019

    Ensure Fragment OnBackPressedCallbacks take priority
   
    As FragmentController is not yet driven by a
    LifecycleObserver (b/127528777), LifecycleObservers on
    Fragments are not necessarily nested within
    LifecycleObservers registered at the Activity level.
    This can lead to cases where a Fragment is started
    before the Activity's Lifecycle is started.
   
    In the case of FragmentManager's usage of Lifecycle to
    add OnBackPressedCallbacks, that nesting is critical
    to ensure the ordering of callbacks. By creating a
    host level Lifecycle that is exactly nested outside
    the callbacks to FragmentController, we can ensure
    the proper nesting in callbacks.
   
    Test: added test passes
    Change-Id: I958d2389c90dcd9d157c6c3d30dffb689ed40c62

M       fragment/src/androidTest/AndroidManifest.xml
M       fragment/src/androidTest/java/androidx/fragment/app/OnBackPressedCallbackTest.kt
M       fragment/src/main/java/androidx/fragment/app/FragmentActivity.java

https://android-review.googlesource.com/948209
https://goto.google.com/android-sha1/85c1de7395f07e3256a50706d4f619e654624250

FWIW, I think this is a fantastic idea and would go a long way in bringing sanity to the world of lifecycle. As it would change the ordering between Activity lifecycle methods and Fragment lifecycle methods, this will almost certainly be an opt-in flag set at the FragmentActivity level.