Android Q, uiMode, and Configuration Changes

If you are a regular follower of my blog posts, I have complete confidence that
you are a fine Android app developer and that all of your apps support configuration changes.

However, there seem to be a lot of apps out there that don���t.

In many cases, that is because the apps do not support orientation changes.
The UIs are locked to portrait or landscape. Orientation changes are the most
common source of configuration changes on phones. The other configuration
change triggers are less common, with the second-most common one probably
being changing locale. So, some developers think they can skip dealing with
configuration changes.

Android Q puts far greater emphasis on the uiMode configuration change, though.
That gets invoked whenever the device switches between normal and dark mode.
The user might do that manually, and it might kick in when the device battery
gets low. It would not shock me if some devices offer other options for automatically
toggling into dark mode, just as stock Android 9.0 offers time-based
���night light��� mode (a blue light filter).

And, if your app does not handle configuration changes properly, your UI will
lose context when the device switches between normal and dark mode, as your
visible activities and their fragments get destroyed and recreated. Symptoms
include:

Losing information in your widgets, because that information is not part
of automatic saved instance state logic (e.g., enabled status)

Forgetting about a dialog, because you are showing it directly instead of using a
DialogFragment, so the dialog vanishes after the configuration change

Reloading data from disk or the network, because you are not using
a ViewModel, retained fragment, or other way to keep that data around across
the configuration change

So, even if your UI is locked to a single orientation, please add configuration
change support. Android Q gives us another easy way to test configuration
changes: add the ���Dark Theme��� tile to the notification shade, then toggle between
normal and dark modes using the tile.

Also, if you are manually managing configuration changes via android:configChanges,
there is a good chance you will want to manage uiMode manually as well. For
example, if your app involves continuous playback (e.g., a video player), you
might not want to interrupt playback just because the device switched between
normal and dark mode.