As of Jetpack Compose, a Recycler type of view is called Lazy.
For now, there are only Lazy Row and Lazy Column.
I have a Staggered Grid custom Composable, that is scrollable. But is there a way I can make it Lazy? Or is such an API not stable yet?
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2 Answers
You can do the same effect in many ways, one of them is:
@Composable
fun StaggeredVerticalGrid(
modifier: Modifier = Modifier,
maxColumnWidth: Dp,
children: @Composable () -> Unit
) {
Layout(
children = children,
modifier = modifier
) { measurables, constraints ->
check(constraints.hasBoundedWidth) {
"Unbounded width not supported"
}
val columns = ceil(constraints.maxWidth / maxColumnWidth.toPx()).toInt()
val columnWidth = constraints.maxWidth / columns
val itemConstraints = constraints.copy(maxWidth = columnWidth)
val colHeights = IntArray(columns) { 0 } // track each column's height
val placeables = measurables.map { measurable ->
val column = shortestColumn(colHeights)
val placeable = measurable.measure(itemConstraints)
colHeights[column] += placeable.height
placeable
}
val height = colHeights.maxOrNull()?.coerceIn(constraints.minHeight, constraints.maxHeight)
?: constraints.minHeight
layout(
width = constraints.maxWidth,
height = height
) {
val colY = IntArray(columns) { 0 }
placeables.forEach { placeable ->
val column = shortestColumn(colY)
placeable.place(
x = columnWidth * column,
y = colY[column]
)
colY[column] += placeable.height
}
}
}
}
private fun shortestColumn(colHeights: IntArray): Int {
var minHeight = Int.MAX_VALUE
var column = 0
colHeights.forEachIndexed { index, height ->
if (height < minHeight) {
minHeight = height
column = index
}
}
return column
}
extracted from Owl sample app, Don't forget to wrap/call this Composable inside ScrollableColumn.
EDIT: with the release of compose 1.0.0-alpha09, now you have official LazyVerticalGrid, check release notes
4 Comments
Ahmad Sattout
LazyVerticalGrid does not I clude a StaggeredGrid behaviour
MR3YY
No Problem, you can still copy-paste code snippet above it has the staggered effect and also you can customize it as you want
Ahmad Sattout
Yeah, only problem is, it won't be Lazy
MR3YY
You're right, both solutions have some caveats. you'll need to wrap/customize
LazyVerticalGrid to achieve staggered effect if you want something perfectIf you are implementing a custom staggered grid, I would say you implement a staggered row instead. Then create another Composable that receives the data and feeds it in the staggered rows while internally using a lazy column for each row. I am not asking you to implement something new. Just tweak the existing implementation a bit and it will be a great performance boost.
Also, if your data is not big enough, it is okay to not use lazy containers.
answered Jun 11, 2021 at 21:29
Richard Onslow Roper
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2 Comments
Psijic
What is considered big here?
Richard Onslow Roper
Anything that causes a "lag" in the scroll. You should take the threshold from the lowest performing processor available, so that it works smoothly on all the devices. If the data is able to get displayed lag-free on athe lowest-end device, it'll work fine on every other device even without the lazy layouts. Else, you should divert to using lazy layouts.