ReorderableColumn for Jetpack Compose
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@Stable | |
class ReorderableColumnState( | |
private val onReorder: (oldIndex: Int, newIndex: Int) -> Unit, | |
) { | |
internal var reordering by mutableStateOf(false) | |
internal var draggingItemIndex: Int = -1 | |
internal var newTargetIndex by mutableStateOf(-1) | |
internal var offsetY by mutableStateOf(0f) | |
internal var childSizes = arrayListOf<IntSize>() | |
fun start(index: Int) { | |
draggingItemIndex = index | |
reordering = true | |
} | |
fun drag(y: Float) { | |
offsetY += y | |
if (offsetY.roundToInt() == 0) { | |
return | |
} | |
val newOffset = | |
(childSizes.subList(0, draggingItemIndex).sumOf { it.height } + offsetY).roundToInt() | |
newTargetIndex = ArrayList(childSizes) | |
.apply { | |
removeAt(draggingItemIndex) | |
} | |
.map { it.height } | |
.runningReduce { acc, i -> acc + i } | |
.let { it + newOffset } | |
.sortedBy { it } | |
.indexOf(newOffset) | |
.let { | |
if (offsetY < 0) { | |
it + 1 | |
} else { | |
it | |
} | |
} | |
} | |
fun cancel() { | |
reordering = false | |
draggingItemIndex = -1 | |
newTargetIndex = -1 | |
offsetY = 0f | |
} | |
fun drop() { | |
if (offsetY.roundToInt() == 0) { | |
return | |
} | |
val newOffset = | |
(childSizes.subList(0, draggingItemIndex).sumOf { it.height } + offsetY).roundToInt() | |
val newIndex = ArrayList(childSizes) | |
.apply { | |
removeAt(draggingItemIndex) | |
} | |
.map { it.height } | |
.runningReduce { acc, i -> acc + i } | |
.let { it + newOffset } | |
.sortedBy { it } | |
.indexOf(newOffset) | |
.let { | |
if (offsetY < 0) { | |
it + 1 | |
} else { | |
it | |
} | |
} | |
onReorder.invoke(draggingItemIndex, newIndex) | |
reordering = false | |
draggingItemIndex = -1 | |
newTargetIndex = -1 | |
offsetY = 0f | |
} | |
} | |
@Composable | |
fun <T> ReorderableColumn( | |
modifier: Modifier = Modifier, | |
data: List<T>, | |
state: ReorderableColumnState, | |
dragingContent: @Composable ((T) -> Unit)? = null, | |
itemContent: @Composable (T) -> Unit, | |
) { | |
Layout( | |
modifier = modifier | |
.verticalScroll(rememberScrollState()), | |
content = { | |
data.forEachIndexed { index, item -> | |
Box( | |
modifier = Modifier | |
.pointerInput(Unit) { | |
detectDragGesturesAfterLongPress( | |
onDragCancel = { | |
state.cancel() | |
}, | |
onDragEnd = { | |
state.drop() | |
}, | |
onDragStart = { | |
state.start(index) | |
}, | |
onDrag = { _, dragAmount -> | |
state.drag(dragAmount.y) | |
} | |
) | |
} | |
.let { | |
if (state.reordering && state.draggingItemIndex == index) { | |
it.zIndex(0.1f) | |
} else { | |
it.zIndex(0f) | |
} | |
} | |
) { | |
if (state.reordering && state.draggingItemIndex == index && dragingContent != null) { | |
dragingContent.invoke(item) | |
} else { | |
itemContent.invoke(item) | |
} | |
} | |
} | |
} | |
) { measurables, constraints -> | |
val placeables = measurables.map { | |
it.measure(constraints) | |
} | |
state.childSizes.clear() | |
state.childSizes.addAll(placeables.map { | |
IntSize( | |
width = it.measuredWidth, | |
height = it.measuredHeight | |
) | |
}) | |
layout( | |
width = placeables.maxOf { it.measuredWidth }, | |
height = placeables.sumOf { it.measuredHeight } | |
) { | |
var height = 0 | |
placeables.forEachIndexed { index, placeable -> | |
if (state.reordering && index == state.newTargetIndex && index != state.draggingItemIndex && state.offsetY < 0) { | |
height += placeables[state.draggingItemIndex].height | |
} | |
if (state.reordering && index == state.draggingItemIndex) { | |
placeable.place(0, (height + state.offsetY.roundToInt()).let { | |
if (state.newTargetIndex != -1 && index != state.newTargetIndex && state.offsetY < 0) { | |
it - placeables[state.newTargetIndex].height | |
} else { | |
it | |
} | |
}) | |
} else { | |
placeable.place(0, height) | |
} | |
if (state.reordering && index == state.newTargetIndex && index != state.draggingItemIndex && state.offsetY > 0) { | |
height += placeables[state.draggingItemIndex].height | |
} | |
if (!state.reordering || index != state.draggingItemIndex || state.newTargetIndex == -1 || index == state.newTargetIndex) { | |
height += placeable.measuredHeight | |
} | |
} | |
} | |
} | |
} |
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