How to specify the order of back press handlers?

[evjava]

I want to specify the order of handlers like follows:

1. close drawer (if open)
2. close search (if expanded)
3. handle backpress by component (if can)
4. router.pop
5. handle double-press (first press for toast "press twice to exit", second quick press for exit)

I can implement all these handlers, but I don't understand, how to tangle them together in correct order.

Is there some API to do it? As I see, the order isn't specified, moreover, router calls pop after other handlers.

Sub question: is it possible to access router.backstackSize from outside? Probably it can help me.

[arkivanov]

Hello and thanks for the question!

As I see, the order isn't specified

The BackPresessedHandler is part of the Essenty library. And the order is specified in the README file. All registered callbacks are called in reverse order. This reflects the behaviour of the the AndroidX OnBackPressedDispatcher.

I can implement all these handlers, but I don't understand, how to tangle them together in correct order.

Based on what you described, I suggest the following implementation. First, you can avoid passing the handleBackButton flag to the ComponentContext.router(...) method. This will allow manual back button handling. Next, perhaps you can register just one callback to the BackButtonHandler and do checks and actions there. Return true to intercept the back button handling, or false to allow other registered callbacks.

is it possible to access router.backstackSize from outside?

Yes it is possible. Will router.state.value.backstack.size work for you?

[arkivanov]

Or if the drawer/search logic is in a child component, then the following approach can help.

In a child component:

backPressedHandler.register {
    when {
        drawer.isOpen -> {
            drawer.close()
            true
        }
        search.isOpen -> {
            search.close()
            true
        }
        else -> {
            // Handle the back button
            true | false // Return true to intercept the event or false to allow other callbacks
        }
    }
}

In the root:

init {
    backPressedHandler.register {
        // Called if none of the children intercepted the event and the router has nothing to pop
        // Check the timeout and show the toast if needed
        true | false  // Return true if the toast was shown, false otherwise
    }
}

private val router = router(handleBackButton = true, ...)

[evjava]

> Next, perhaps you can register just one callback to the BackButtonHandler and do checks and actions there.

Yep, it works, thanks!

> Will router.state.value.backstack.size work for you?

Yes. I didn't notice it.. 🤔