IssueTracker

Project: platform/frameworks/support
Branch: androidx-main
Author: Louis Pullen-Freilich <lpf@google.com>
Link:      https://android-review.googlesource.com/3328184

Adds OverscrollEffect#withoutDrawing and OverscrollEffect#withoutEventHandling

Adds OverscrollEffect#withoutDrawing and OverscrollEffect#withoutEventHandling 
 
These APIs allow overscroll to have events dispatched to it by one component, and rendered in a separate component. 
 
Fixes: b/266550551 
Fixes: b/204650733 
Fixes: b/255554340 
Fixes: b/229537244 
Test: OverscrollTest 
Relnote: "Adds OverscrollEffect#withoutDrawing and OverscrollEffect#withoutEventHandling APIs - these APIs create a wrapped instance of the provided overscroll effect that doesn't draw / handle events respectively, which allows for rendering  overscroll in a separate component from the component that is dispatching events. For example, disabling drawing the overscroll inside a lazy list, and then drawing the overscroll separately on top / elsewhere." 
Change-Id: Idbb3d91546b49c1987a041f959bce4b2b09a9f61

The following release(s) address this bug.It is possible this bug has only been partially addressed:

• androidx.compose.foundation:foundation:1.8.0-alpha06
• androidx.compose.foundation:foundation-android:1.8.0-alpha06
• androidx.compose.foundation:foundation-jvmstubs:1.8.0-alpha06
• androidx.compose.foundation:foundation-linuxx64stubs:1.8.0-alpha06

Any chance for a release including this fix soon?

There’s already a dedicated issue about the back not working when android:enableOnBackInvokedCallback=“true” is set: https://issuetracker.google.com/issues/281967264

It seems like it’s blocked by a general lack of predictive back support in Compose, though: https://issuetracker.google.com/issues/281967264#comment3

I've tried androidx.compose.material3:material3:1.2.0-beta01 and I believe it's still not working. BackHandler {} is not called inside ModalBottomSheet, the sheet is closing instead.

The fix wasn't to support BackHandler {}. They just added a new properties arg that you can set whether the sheet should be dismissed on back or not:

ModalBottomSheet(
  ...
  properties = ModalBottomSheetDefaults.properties(shouldDismissOnBackPress = /* boolean goes here */),
  ...
)

Since the sheet is in a separate window, I'm afraid this might be the best they can do. That's pretty similar to the API of dialogs, which also have their own window:

Dialog(
  ...
  properties = DialogProperties(dismissOnBackPress = /* boolean goes here */),
  ...
)

But of course the APIs aren't super consistent 😅

The bug as it's stated in the title and the snippet still exists despite the "fix": it remains impossible to use a BackHandler inside a ModalBottomSheet.

Some thoughts after looking at the code: somehow the ModalBottomSheetWindow needs to implement a OnBackPressedDispatcherOwner and delegate to it when back is pressed (in dispatchKeyEvent), instead of directly calling onDismissRequest like it does today (material3 version 1.2.0). I note that the "ModalBottomSheetWindow" is actually a View, not a Window -- perhaps that's why this is not trivial to fix.

Knowing the code doesn't give me a good idea for a workaround though...

I have found a workaround. It consists in intercepting the key event, doing the same checks that ModalBottomSheetWindow.dispatchKeyEvent would do, and then delegating that to the OnBackPressedDispatcherOwner manually.

@Composable
fun ModalBottomSheetWithBackHandling(
    onDismissRequest: () -> Unit,
    modifier: Modifier = Modifier,
    sheetState: SheetState = rememberModalBottomSheetState(),
    properties: ModalBottomSheetProperties = ModalBottomSheetDefaults.properties(),
    content: @Composable ColumnScope.() -> Unit,
) {
    val scope = rememberCoroutineScope()

    BackHandler(enabled = sheetState.targetValue != SheetValue.Hidden) {
        // Always catch back here, but only let it dismiss if shouldDismissOnBackPress.
        // If not, it will have no effect.
        if (properties.shouldDismissOnBackPress) {
            scope.launch { sheetState.hide() }.invokeOnCompletion {
                if (!sheetState.isVisible) {
                    onDismissRequest()
                }
            }
        }
    }

    val requester = remember { FocusRequester() }
    val backPressedDispatcherOwner = LocalOnBackPressedDispatcherOwner.current

    ModalBottomSheet(
        onDismissRequest = onDismissRequest,
        modifier = modifier
            .focusRequester(requester)
            .focusable()
            .onPreviewKeyEvent {
                if (it.key == Key.Back && it.type == KeyEventType.KeyUp && !it.nativeKeyEvent.isCanceled) {
                    backPressedDispatcherOwner?.onBackPressedDispatcher?.onBackPressed()
                    return@onPreviewKeyEvent true
                }
                return@onPreviewKeyEvent false
            },
        properties = ModalBottomSheetDefaults.properties(
            securePolicy = properties.securePolicy,
            isFocusable = properties.isFocusable,
            // Set false otherwise the onPreviewKeyEvent doesn't work at all.
            // The functionality of shouldDismissOnBackPress is achieved by the BackHandler.
            shouldDismissOnBackPress = false,
        ),
        content = content,
    )

    LaunchedEffect(Unit) {
        requester.requestFocus()
    }
}

Thank you for your workaround code!

The problem is if you're using focusManager.clearFocus() anywhere in your code the ModalBottomSheet will lose focus.

BackHandler seems to be working in androidx.compose.material3:material3:1.3.0-beta02 out of the box without the workaround I posted a couple of messages above.