Jetpack Compose simple number picker

ComposeNumberPicker.kt

@Composable
fun NumberPicker(
    state: MutableState<Int>,
    modifier: Modifier = Modifier,
    range: IntRange? = null,
    textStyle: TextStyle = LocalTextStyle.current,
    onStateChanged: (Int) -> Unit = {},
) {
    val coroutineScope = rememberCoroutineScope()
    val numbersColumnHeight = 36.dp
    val halvedNumbersColumnHeight = numbersColumnHeight / 2
    val halvedNumbersColumnHeightPx = with(LocalDensity.current) { halvedNumbersColumnHeight.toPx() }

    fun animatedStateValue(offset: Float): Int = state.value - (offset / halvedNumbersColumnHeightPx).toInt()

    val animatedOffset = remember { Animatable(0f) }.apply {
        if (range != null) {
            val offsetRange = remember(state.value, range) {
                val value = state.value
                val first = -(range.last - value) * halvedNumbersColumnHeightPx
                val last = -(range.first - value) * halvedNumbersColumnHeightPx
                first..last
            }
            updateBounds(offsetRange.start, offsetRange.endInclusive)
        }
    }
    val coercedAnimatedOffset = animatedOffset.value % halvedNumbersColumnHeightPx
    val animatedStateValue = animatedStateValue(animatedOffset.value)

    Column(
        modifier = modifier
            .wrapContentSize()
            .draggable(
                orientation = Orientation.Vertical,
                state = rememberDraggableState { deltaY ->
                    coroutineScope.launch {
                        animatedOffset.snapTo(animatedOffset.value + deltaY)
                    }
                },
                onDragStopped = { velocity ->
                    coroutineScope.launch {
                        val endValue = animatedOffset.fling(
                            initialVelocity = velocity,
                            animationSpec = exponentialDecay(frictionMultiplier = 20f),
                            adjustTarget = { target ->
                                val coercedTarget = target % halvedNumbersColumnHeightPx
                                val coercedAnchors = listOf(-halvedNumbersColumnHeightPx, 0f, halvedNumbersColumnHeightPx)
                                val coercedPoint = coercedAnchors.minByOrNull { abs(it - coercedTarget) }!!
                                val base = halvedNumbersColumnHeightPx * (target / halvedNumbersColumnHeightPx).toInt()
                                coercedPoint + base
                            }
                        ).endState.value

                        state.value = animatedStateValue(endValue)
                        onStateChanged(state.value)
                        animatedOffset.snapTo(0f)
                    }
                }
            )
    ) {
        val spacing = 4.dp

        val arrowColor = MaterialTheme.colors.onSecondary.copy(alpha = ContentAlpha.disabled)

        Arrow(direction = ArrowDirection.UP, tint = arrowColor)

        Spacer(modifier = Modifier.height(spacing))

        Box(
            modifier = Modifier
                .align(Alignment.CenterHorizontally)
                .offset { IntOffset(x = 0, y = coercedAnimatedOffset.roundToInt()) }
        ) {
            val baseLabelModifier = Modifier.align(Alignment.Center)
            ProvideTextStyle(textStyle) {
                Label(
                    text = (animatedStateValue - 1).toString(),
                    modifier = baseLabelModifier
                        .offset(y = -halvedNumbersColumnHeight)
                        .alpha(coercedAnimatedOffset / halvedNumbersColumnHeightPx)
                )
                Label(
                    text = animatedStateValue.toString(),
                    modifier = baseLabelModifier
                        .alpha(1 - abs(coercedAnimatedOffset) / halvedNumbersColumnHeightPx)
                )
                Label(
                    text = (animatedStateValue + 1).toString(),
                    modifier = baseLabelModifier
                        .offset(y = halvedNumbersColumnHeight)
                        .alpha(-coercedAnimatedOffset / halvedNumbersColumnHeightPx)
                )
            }
        }

        Spacer(modifier = Modifier.height(spacing))

        Arrow(direction = ArrowDirection.DOWN, tint = arrowColor)
    }
}

@Composable
private fun Label(text: String, modifier: Modifier) {
    Text(
        text = text,
        modifier = modifier.pointerInput(Unit) {
            detectTapGestures(onLongPress = {
                // FIXME: Empty to disable text selection
            })
        }
    )
}

private suspend fun Animatable<Float, AnimationVector1D>.fling(
    initialVelocity: Float,
    animationSpec: DecayAnimationSpec<Float>,
    adjustTarget: ((Float) -> Float)?,
    block: (Animatable<Float, AnimationVector1D>.() -> Unit)? = null,
): AnimationResult<Float, AnimationVector1D> {
    val targetValue = animationSpec.calculateTargetValue(value, initialVelocity)
    val adjustedTarget = adjustTarget?.invoke(targetValue)

    return if (adjustedTarget != null) {
        animateTo(
            targetValue = adjustedTarget,
            initialVelocity = initialVelocity,
            block = block
        )
    } else {
        animateDecay(
            initialVelocity = initialVelocity,
            animationSpec = animationSpec,
            block = block,
        )
    }
}

NumberPickerSample.kt

@Preview
@Composable
fun PreviewNumberPicker() {
    Box(modifier = Modifier.fillMaxSize()) {
        NumberPicker(
            state = remember { mutableStateOf(9) },
            range = 0..10,
            modifier = Modifier.align(Alignment.Center)
        )
    }
}

Hey @vganin. Thanks for the great implementation. I want another implementation like this one but it should be automatically scrolled. Imagine this: we have two cards with this number picker. one has 60 numbers and another one has 10. the animation speed for both of them should be 3000 ms and they should start simultaneously. Can you help me build this?

Do you mean like when you scroll one picker, then the other scrolls automatically as if you would scroll them simultaneously? Maybe sharing single MutableInteractionSource using remember between two pickers is what you want?

Hey @vganin Thanks for this amazing implementation, I want to ask you about the licence, Is it available under Apache 2.0 license?

Hey @vganin Thanks for this amazing implementation, I want to ask you about the licence, Is it available under Apache 2.0 license?

You're very welcome. Yes, it is. This code is actually a part of my open-source app, and the license can be found here.

There is a generic version here with wrapSelectorWheel parameter