Hey Composers! I have a question about <https://developer.android.com/reference/kotlin/androidx/comp...

# compose

[alaershov]

Hey Composers! I have a question about Material 3 ModalBottomSheet and handling the Back button

I want to forbid closing current bottom sheet depending on some logical state - for instance, if a critical action is in progress, don't allow closing the sheet. I was able to make it work in Material 2 implementation, and now I'm struggling with Material 3.

ModalBottomSheet has SheetState, which has confirmValueChange - a callback that I use to forbid ModalBottomSheet dismiss depending on its logical state. This works fine with "tap outside sheet" and "drag sheet down" dismiss actions. However, a system Back button press does not respect confirmValueChange - it just dismisses the sheet without any hesitation.
There are ModalBottomSheetProperties, such as shouldDismissOnBackPress. Unfortunately, setting shouldDismissOnBackPress=false just disables the back button completely - the sheet's Window intercepts it, but does nothing.
BackHandler also doesn't work, as it requires underlying support in the implementation of Window. Dialog composable has this support, but not ModalBottomSheet.

Basically, I want everything to work exaclty as it does, except make back button press respect confirmValueChange. I even tried copying MaterialBottomSheet sources to modify this behavior, but it's a banana-monkey-jungle problem, too much stuff is internal.

Any advice on how to make this work? Thanks in advance!

[Joel Denke]

You need to override the back press dispatcher API as well, to ignore back press. Or using BackHandler.
I can also throw in I strongly advice using this UX pattern, never block user from pressing back to close.
If critical action, just re-open it again next time same action need to happen imo or something else 🙂

[alaershov]

You're absolutely right about the UX side, but the technical question still stands)

BackHandler does not work in Material 3 Bottom Sheet - it opens as a Window (ModalBottomSheetWindow to be precise), and it lacks support for back handlers

[Joel Denke]

Dont use the bottomsheet at all for back handling is what I am saying 🙂 Ignore whatever Google doing.

[alaershov]

I open Material 3 bottom sheet, and there is no way to override it's back button handling. I can either disable it completely (then nothing happens, as back press is handled by sheets Window anyway), or go with the default implementation

[Joel Denke]

Just do like:
Box {
BackHandler()
ModalBottomSheet()
}

[alaershov]

this back handler will be ignored becasue Window inside ModalBottomSheet intercepts back presses

[Joel Denke]

I am using like this without any issues:

val sheetState = rememberModalBottomSheetState(skipPartiallyExpanded = true)
        val coroutineScope = rememberCoroutineScope()
        BackHandler(enabled = sheetState.isVisible) {
            coroutineScope
                .launch { sheetState.hide() } // Ignore in your case
                .invokeOnCompletion {
                    if (!sheetState.isVisible) {
                        // do something
                    }
                }
        }

        ModalBottomSheet(
            modifier = Modifier.fillMaxWidth(),
            content = {
                content(model)
            },
            sheetState = sheetState,
            onDismissRequest = { navigator.finish(onDismiss()) },
        )

[Joel Denke]

Not sure what you mean with WIndow inside intercept, why would it do that?

[alaershov]

are you sure your backhandler works? because by default ModalBottomSheet will intercept back press and will close internally.

[Joel Denke]

Yeah it works

[alaershov]

Not sure what you mean with WIndow

Material 3 Bottom Sheet is implemented internally as a ModalBottomSheetWindow. It handles back press, because if you have more than one open Window, the back press is dispatched to the topmost one, which is ModalBottomSheetWindow

[Joel Denke]

One major difference in my case I am using Circuit Overlay to display the bottomsheet, if that impacts maybe 🙂

[alaershov]

Yeah it works

try removing everything inside your BackHandler - I bet back button will still close your bottom sheet

[alaershov]

what is Circle Overlay?

[Joel Denke]

https://github.com/slackhq/circuit/tree/main/circuit-overlay

[Joel Denke]

"try removing everything inside your BackHandler - I bet back button will still close your bottom sheet"
Yeah ofc as I want it to be dismissed 😛 But I will try what you say, to check, sounds interesting.

[alaershov]

I mean it just as a scientific experiment) If you think your BackHandler works - try removing it. If back press still works, then maybe it wasn't working due to BackHandler after all)

[Joel Denke]

Yeah its interesting, seems still work.

[alaershov]

> I am using Circuit Overlay
yeah, this could be it as well, there is some under-the-hood magic in Circuit for sure

[Joel Denke]

Circuit 😄

[Joel Denke]

Adding properties = ModalBottomSheetDefaults.properties(shouldDismissOnBackPress = false) ignores back press on bottomsheet.
WIll now try combine everything to see how behaves.

[Joel Denke]

Right, yeah I get same problem as you now, sorry 😄

[alaershov]

yes it does, but it does NOT make backhandler work!

[alaershov]

Thanks, friend, at least now I know I'm not insane)

[alaershov]

TL;DR of the thread for future brave heroes: the problem in the original post is reproducible and not solved yet)

[Joel Denke]

I got interested and will check source code of what the heck Google did here, seems insane.

[alaershov]

You're in for a wondrous journey)

[Joel Denke]

Haha yeah kill me, are we going back in time with WIndowManager now 😄 I will stop using Googles things if this is the new thing

[Joel Denke]

Feels like DIalogFragment but for Compose AbstractView now 😄

[alaershov]

Yeah, looks not ideal, to say the least

[Joel Denke]

override fun onAttachedToWindow() {
        super.onAttachedToWindow()

        maybeRegisterBackCallback()
    }

    override fun onDetachedFromWindow() {
        super.onDetachedFromWindow()

        maybeUnregisterBackCallback()
    }

    private fun maybeRegisterBackCallback() {
        if (!properties.shouldDismissOnBackPress || Build.VERSION.SDK_INT < 33) {
            return
        }
        if (backCallback == null) {
            backCallback = Api33Impl.createBackCallback(onDismissRequest)
        }
        Api33Impl.maybeRegisterBackCallback(this, backCallback)
    }

    private fun maybeUnregisterBackCallback() {
        if (Build.VERSION.SDK_INT >= 33) {
            Api33Impl.maybeUnregisterBackCallback(this, backCallback)
        }
        backCallback = null
    }

This wants me go hide and never look at this code again ...

[Stylianos Gakis]

Is it possible that you are using enableOnBackInvokedCallback on your manifest and not the latest material3 library and are hitting this https://issuetracker.google.com/issues/281967264?

[alaershov]

Thanks, but sadly no( dismiss works fine, and the code is the same, there just isn't enough customization options, and I have to copy-paste the entire thing to tweak it. Open/closed principle is too closed in this case)

[Alex Vanyo]

Which material3 version are you reproducing the issue with?

[Joel Denke]

Not sure if @alaershov using same, but I use:
https://github.com/JetBrains/compose-multiplatform/releases/tag/v1.6.0-rc03
Which refers to version Material3 1.2.0
Thats reproduce the issue for me as well.
I think there was some kind of bug fix for this in M2 1.3.0.alpha01 or? I refer to https://issuetracker.google.com/issues/281967264#comment7

[alaershov]

1.2.0 for me as well, using BOM 2024.02.01

[alaershov]

I don't thinkk this is the fix @Joel Denke, looks more like additional support for predictive back on the newest API

[alaershov]

@Alex Vanyo can you tell us if ignoring confirmValueChange is a deliberate design decision for back button handling in Material 3 ModalBottomSheet? It's a reasonable default for sure, but would be nice to allow the user to customize it.

[Jacob Rhoda]

I am the brave hero. Thanks for confirming I'm not crazy. Anyone have a workaround?

[alaershov]

@Jacob Rhoda I ended up copying the whole Material 3 ModalBottomSheet implementation to my project just to fix this one issue.
There is a probable fix in https://developer.android.com/jetpack/androidx/releases/compose-material3#1.3.0-alpha06
ModalBottomSheet is now written as a Dialog instead of popup, so maybe back handler works now