kotlin - Android Compose: How to detect drag stop (finger lifted) when using Modifier.verticalScroll - Stack Overflow

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If I make a column vertically scrollable with Modifier.verticalScroll() then try to detect a drag stop using detectVerticalDragGestures this breaks the scrolling.

Column(
    modifier = Modifier
        .verticalScroll(innerScrollState)
        .pointerInput(Unit) {
            detectVerticalDragGestures(  // <- breaks scrolling
                onDragEnd = {
                    // Do something here
                }
            ) { change, dragAmount ->  }
        }
        .nestedScroll(scrollConnection)
        .fillMaxWidth()
)

What options do I have to detect the user has lifted his finger while maintaining scrollability, including the nestedScroll I have setup.

If I make a column vertically scrollable with Modifier.verticalScroll() then try to detect a drag stop using detectVerticalDragGestures this breaks the scrolling.

Column(
    modifier = Modifier
        .verticalScroll(innerScrollState)
        .pointerInput(Unit) {
            detectVerticalDragGestures(  // <- breaks scrolling
                onDragEnd = {
                    // Do something here
                }
            ) { change, dragAmount ->  }
        }
        .nestedScroll(scrollConnection)
        .fillMaxWidth()
)

What options do I have to detect the user has lifted his finger while maintaining scrollability, including the nestedScroll I have setup.

• android
• kotlin

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2 Answers 2

Sorted by: Reset to default 0

You can check the isScrollInProgress parameter of the scroll state, but I'm not sure it's enough with a custom nestedScroll:

val scrollState = rememberScrollState()
val scrollBehavior = TopAppBarDefaults.enterAlwaysScrollBehavior()

LaunchedEffect(scrollState) {
    snapshotFlow { scrollState.isScrollInProgress }
        .collect { isScrollInProgress ->
            if (!isScrollInProgress) {
                /** doSomething **/
            }
        }
}

Scaffold(
    modifier = Modifier.nestedScroll(scrollBehavior.nestedScrollConnection),
    topBar = {
        TopAppBar(
            title = { Text("TopAppBar") },
            navigationIcon = {
                IconButton(onClick = { /** doSomething **/ }) {
                    Icon(
                        imageVector = Icons.Filled.Menu,
                        contentDescription = null
                    )
                }
            },
            scrollBehavior = scrollBehavior
        )
    },
) { paddingValues ->
    Column(
        Modifier
            .fillMaxSize()
            .verticalScroll(scrollState)
            .padding(paddingValues)
    ) {
        repeat(200) {
            Text(modifier = Modifier.fillMaxWidth(), text = "Title")
        }
    }
}

In case this helps someone, I dont know if this is the best answer. But if you use pointerInput but don't use detectDragXXX instead do your own, you can observe the values without breaking scrollable. Its not quite as good as dragStart and Stop, but it worked for my needs:

.pointerInput(Unit) {
  awaitPointerEventScope {
    while (true) {
      val event = awaitPointerEvent()
      event.changes.forEach { change ->
        if (change.pressed && !change.previousPressed) { finger down }
        if (!change.pressed) { finger up }
      }
    }
  }
}

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