Bottom sheet

bottomsheet.kt

enum class States {
    EXPANDED,
    COLLAPSED
}

@ExperimentalMaterialApi
@Composable
fun FullHeightBottomSheet(
    header: @Composable () -> Unit,
    body: @Composable () -> Unit
) {
    val swipeableState = rememberSwipeableState(initialValue = States.EXPANDED)
    val scrollState = rememberScrollState()

    BoxWithConstraints {
        val constraintsScope = this
        val maxHeight = with(LocalDensity.current) {
            constraintsScope.maxHeight.toPx()
        }

        val connection = remember {
            object : NestedScrollConnection {

                override fun onPreScroll(
                    available: Offset,
                    source: NestedScrollSource
                ): Offset {
                    val delta = available.y
                    return if (delta < 0) {
                        swipeableState.performDrag(delta).toOffset()
                    } else {
                        Offset.Zero
                    }
                }

                override fun onPostScroll(
                    consumed: Offset,
                    available: Offset,
                    source: NestedScrollSource
                ): Offset {
                    val delta = available.y
                    return swipeableState.performDrag(delta).toOffset()
                }

                override suspend fun onPreFling(available: Velocity): Velocity {
                    return if (available.y < 0 && scrollState.value == 0) {
                        swipeableState.performFling(available.y)
                        available
                    } else {
                        Velocity.Zero
                    }
                }

                override suspend fun onPostFling(
                    consumed: Velocity,
                    available: Velocity
                ): Velocity {
                    swipeableState.performFling(velocity = available.y)
                    return super.onPostFling(consumed, available)
                }

                private fun Float.toOffset() = Offset(0f, this)
            }
        }

        Box(
            Modifier
                .swipeable(
                    state = swipeableState,
                    orientation = Orientation.Vertical,
                    anchors = mapOf(
                        0f to States.EXPANDED,
                        maxHeight to States.COLLAPSED,
                    )
                )
                .nestedScroll(connection)
                .offset {
                    IntOffset(
                        0,
                        swipeableState.offset.value.roundToInt()
                    )
                }
        ) {
            Column(
                Modifier
                    .fillMaxHeight()
                    .background(Color.White)
            ) {
                header()
                Box(
                    Modifier
                        .fillMaxWidth()
                        .verticalScroll(scrollState)
                ) {
                    body()
                }
            }
        }
    }
}

What if in the bottom sheet content will be a lazylist, how we can track then a scrollState ?

@Alexbeard This was my use case as well. I believe I solved it with relatively few modifications.

1. I changed val scrollState = rememberScrollState() to val scrollState = rememberLazyListState().

2. In the onPreFling I changed scrollState.value == 0 to scrollState.firstVisibleItemIndex == 0 && scrollState.firstVisibleItemScrollOffset == 0

The .value in the original implementation describes "current scroll position value in pixels" so what I have accomplishes that I think for the LazyListState implementation of ScrollableState

3. I changed the body part of the content at the end to include a LazyColumn

LazyColumn(
    modifier = Modifier.fillMaxWidth(),
    state = scrollState
) {
    body.invoke(this)
}

4. I changed the body type for this Composable to be body: LazyListScope.() -> Unit,

5. Profit?

I think that's it. It seems to be working, but let it be known that I've been playing around with my implementation for all of about 8 minutes so far

@nkrebs13 8 minutes looks enough for me, ship it!

Hey Guys, Where is the toOffset() method in swipeableState.performDrag(delta).toOffset() coming from? Its not resolving for me.

Oh Sorry, Got it, Didn't see the extension function created below.

Hello, How can I make it so that I can move the bottom sheet only for the area with LazyColumn?

If you want swipeable behavior to occur only when interacting with the actual bottom sheet content Modifier.offset() should be before Modifier.swipeable().

Modifier
    .offset {
        IntOffset(
            0,
            swipeableState.offset.value.roundToInt()
        )
    }
    .swipeable(
        state = swipeableState,
        orientation = Orientation.Vertical,
        anchors = mapOf(
            0f to States.EXPANDED,
            maxHeight to States.COLLAPSED,
        )
    )
    .nestedScroll(connection)

This looks great. One issue I've noticed though is that when the bottom sheet is expanded and you scroll the content, it doesn't use momentum scrolling.

If you want swipeable behavior to occur only when interacting with the actual bottom sheet content Modifier.offset() should be before Modifier.swipeable().

Modifier
    .offset {
        IntOffset(
            0,
            swipeableState.offset.value.roundToInt()
        )
    }
    .swipeable(
        state = swipeableState,
        orientation = Orientation.Vertical,
        anchors = mapOf(
            0f to States.EXPANDED,
            maxHeight to States.COLLAPSED,
        )
    )
    .nestedScroll(connection)

Life Saver. Thank you!!

This is amazing @arcadefire 🪨 ⭐ !!