有一个包含一些数据的常规列表和用于显示它的懒散列.
LazyColumn {
items (list) { item ->
ListItem(item)
}
}
简化ListItem看起来像:
@Composable
fun ListItem(item: SomeItem) {
Row(
modifier = Modifier.fillMaxWidth().height(IntrinsicSize.Min)
) {
//Some widgets
}
}
如果没有足够的项目，我需要设置页脚的项目(列表中最后一个)高度来填充屏幕.很容易找到最后一个项目，并提供一些标志到ListItem(item: SomeItem, isLast: Boolean)，但我不知道如何设置项目的高度，以实现我的目标.有人面临过这个问题吗？
这几乎与我们在这里提出的RecyclerView个问题相同.这个问题的图像说明了这一点.
如果您的项目都是相同的高度，并且通过静态高度或使用Modifier.onSizeChanged{}，您可以通过使用BoxWithConstraints maxHeight或rememberLazyListState().layoutInfo.viewportSize获得懒散列的高度信息
@Composable
private fun ListComposable() {
val myItems = mutableListOf<String>()
repeat(4) {
myItems.add("Item $it")
}
BoxWithConstraints(modifier = Modifier.fillMaxSize()) {
LazyColumn(
modifier = Modifier
.fillMaxSize()
.border(2.dp, Color.Cyan)
) {
itemsIndexed(myItems) { index: Int, item: String ->
if (index == myItems.size - 1) {
Text(
text = item,
modifier = Modifier
.fillMaxWidth()
.height((maxHeight - 50.dp * (myItems.size - 1)).coerceAtLeast(50.dp))
.background(Color.Green)
)
} else {
Text(
text = item,
modifier = Modifier
.fillMaxWidth()
.height(50.dp)
.background(Color.Red)
)
}
}
}
}
}
如果直到最后一项才知道总高度，则需要使用SubcomposeLayout和不包含最后一项的列表，并将LazyColumn height- (items.size-1) total height作为最后一项的高度.
@Composable
fun DimensionMeasureSubcomposeLayout(
modifier: Modifier = Modifier,
mainContent: @Composable () -> Unit,
dependentContent: @Composable (IntSize, Constraints) -> Unit
) {
SubcomposeLayout(modifier = modifier) { constraints ->
// Subcompose(compose only a section) main content and get Placeable
val mainPlaceables: List<Placeable> = subcompose(SlotsEnum.Main, mainContent)
.map {
it.measure(constraints)
}
// Get max width and height of main component
var maxWidth = 0
var maxHeight = 0
mainPlaceables.forEach { placeable: Placeable ->
maxWidth += placeable.width
maxHeight = placeable.height
}
val maxSize = IntSize(maxWidth, maxHeight)
val dependentPlaceables = subcompose(SlotsEnum.Dependent) {
dependentContent(maxSize, constraints)
}.map {
it.measure(constraints)
}
layout(constraints.maxWidth, constraints.maxHeight) {
dependentPlaceables.forEach { placeable: Placeable ->
placeable.placeRelative(0, 0)
}
}
}
}
enum class SlotsEnum { Main, Dependent }
并将其用作
@Composable
private fun SubcomposeExample() {
val myItems = mutableListOf<String>()
repeat(15) {
myItems.add("Item $it")
}
val subList = myItems.subList(0, myItems.size - 1)
val lasItem = myItems.last()
val density = LocalDensity.current
DimensionMeasureSubcomposeLayout(
modifier = Modifier,
mainContent = {
LazyColumn(
modifier = Modifier.fillMaxWidth()
) {
items(subList) { item: String ->
Text(
text = item,
modifier = Modifier
.fillMaxWidth()
.height(50.dp)
.background(Color.Red)
)
}
}
},
dependentContent = { intSize, constraints ->
val lastItemHeight = with(density) {
(constraints.maxHeight - intSize.height).toDp().coerceAtLeast(50.dp)
}
LazyColumn(modifier = Modifier.fillMaxWidth()) {
if (myItems.size > 1) {
items(subList) { item: String ->
Text(
text = item,
modifier = Modifier
.fillMaxWidth()
.height(50.dp)
.background(Color.Red)
)
}
}
item {
Text(
text = lasItem,
modifier = Modifier
.fillMaxWidth()
.height(lastItemHeight)
.background(Color.Green)
)
}
}
}
)
}