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Information

Component used: Activity Version used: 1.3.1 Devices/Android versions reproduced on:

• Samsung Galaxy Tab Active 2 - Android 7.1.1
• Samsung Galaxy XCover Pro - Android 10

Problem description

Docs (Link) for OnBackPressedDispatcher::addCallback clearly states that the

Callbacks are invoked in reverse order in which they are added

Unfortunately the callback order is not restored properly after orientation change, if the callback of a Fragment was added "deferred".

I have attached a little project where the bug can be reproduced:

A MainActivity containing a MainFragment, which gets added deferred (2000 ms). Both the Activity and the Fragment adds an OnBackPressedCallback.

A breakpoint was set in OnBackPressedDispatcher::addCancellableCallback Line 117 to verify the order. This method gets called to finally add the callbacks, if the lifecycle is set to a certain state (CREATED).

If the Application is started, the callback order is

• FragmentManager
• MainActivity
• FragmentManager
• MainFragment

if the device is rotated, the order gets restored as

• FragmentManager
• FragmentManager
• MainFragment
• MainActivity

So the callback order is no longer guaranteed to be in reverse order in which they are added.

Note: if the Fragment is added immediately upon creation of the Activity, the order was restored properly! So the "bug" (I suppose) only occurs if the add-action of a Fragment is deferred.

I have prepared code for both cases in the sample application. (Search for TODO and see the comments in the MainActivity).

Expectation

I would have expected that the order in which the callbacks are added is the same after orientation change as it was before. Regardless if the callback was added at a certain time, the order should be kept the same as right before the orientation change.