Back closes (android) app instead of going back despite handleBackButton = true, and stack being populated

[woj-tek]

I think I have everything setup correctly, yet when I push back button the app closed (goes to main android screen) instead of going back in stack (and there are items in stack). In the root component I have:

	private val router = StackNavigation<Configuration>()

    override val routerState = childStack(
        source = router,
        serializer = Configuration.serializer(),
        initialConfiguration = Configuration.Roster,
        handleBackButton = true,
        childFactory = ::createChild,
    )

Then during navigation I use .pushToFront() (it's a sidemenu/drawer so the user can go A -> B -> C -> B):

router.pushToFront(Configuration.Settings(…)

On each navigation (and push) I see in the logs that the items are correctly added to the stack:

12:16:03.463 Decompose                         W  Current navigation stack: 2: [root.AppRootComponent$Configuration$Roster@edd2729, CallLog(id=-1295932412)]
12:16:11.793 Decompose                         W  Current navigation stack: 3: [root.AppRootComponent$Configuration$Roster@edd2729, CallLog(id=-1295932412), Settings(initialView=main.settings.SettingsComponent$SettingsConfiguration$Menu@82bdba2)]
12:16:43.689 Decompose                         W  Current navigation stack: 4: [root.AppRootComponent$Configuration$Roster@edd2729, CallLog(id=-1295932412), Settings(initialView=main.settings.SettingsComponent$SettingsConfiguration$Menu@82bdba2), root.AppRootComponent$Configuration$CallCreate@eb14c30]

I would assume that handleBackButton = true, should handle it?

[arkivanov]

handleBackButton = true should handle it, indeed. Assuming you correctly initialized the root ComponentContext and there are no other back callbacks registered somewhere in the app (either via Decompose BackHandler or OnBackPressedDispatcher) and interfering the behavior. You can confirm the registered callbacks by placing a breakpoint in ``OnBackPressedDispatcher#onBackPressed` and stepping into any registered callbacks (if there are any).

[woj-tek]

Hmm... I'm kinda stuck/going in circle with this. The problem is that, as I mentioned, we setup the main component in onServiceConnected() and we pass the bound service as a parameter (and then everything else is based on that service). I was pondering this from a couple of angles and whichever approach I thought about/tried everything came back down to said root component being initialised in onServiceConnected(). So a bit of chicken-and-egg problem... any hints would be welcomed :)

[arkivanov]

This looks like a general loading problem. I recommend to create the root component in onCreate and before setContent {}. In the root component, you can define Child Stack with two children: object Child.Disconnected and class Child.Connected(val component: MyServiceComponent). Then initialize the root component with Loading first. Then once the service is connected, call a function in your root component, pass the service/binder there and switch the stack to Connected (using replaceAll). Make sure you navigate always on the main thread. You can also consider disconnecting from the service in onStop.

[woj-tek]

OK. I basically "decomposed" the app to the point where it almost looked like the one from the example (https://arkivanov.github.io/Decompose/getting-started/quick-start/#android-with-compose) so single onCreate() with creation of the component and then setting of the content and while the exact same components/composables worked fine in desktop it was still not working on Android.

And then I noticed the "almost" - in our code we had componentContext = DefaultComponentContext(lifecycle = lifecycle) while the example uses defaultComponentContext() helper... I changed it and suddenly it started to work, even with component being initialized in onServiceConnected() which should not work... but it works :)

Now I wonder why? :D as on the desktop DefaultComponentContext works just fine (with custom handler for "back navigation" mapped to [esc].

[arkivanov]

Now I wonder why?

That's because the root ComponentContext being created as DefaultComponentContext(lifecycle = lifecycle) is disconnected from the Activity's OnBackPressedDispatcher, meaning the Activity is not aware of its internal back stack and just closes when the back is pressed.

The defaultComponentContext() is an extension function that automatically connects Lifecycle, StateKeeper, InstanceKeeper and BackHandler to the hosting Activity. Without it you'd need to manually drive the lifecycle, plus state preservation, instance retaining and back handling won't work.

as on the desktop DefaultComponentContext works just fine (with custom handler for "back navigation" mapped to [esc]).

I think this is because you are passing DefaultComponentContext(..., backHandler = ...) argument on Desktop, which allows back button handling.

[woj-tek]

Thank you so much for the exaplanation :)