LazyListPrefetchStrategy
@ExperimentalFoundationApi
interface LazyListPrefetchStrategy
Implementations of this interface control which indices of a LazyList should be prefetched (precomposed and premeasured during idle time) as the user interacts with it.
Implementations should invoke LazyListPrefetchScope.schedulePrefetch to schedule prefetches
from the onScroll and onVisibleItemsUpdated callbacks. If any of the returned PrefetchHandles
no longer need to be prefetched, use LazyLayoutPrefetchState.PrefetchHandle.cancel to cancel
the request.
Properties
Deprecated Customization of PrefetchScheduler is no longer supported. LazyLayout will attach an appropriate scheduler internally.
val prefetchScheduler: PrefetchScheduler?
A PrefetchScheduler implementation which will be used to execute prefetch requests for this
strategy implementation. If null, the default PrefetchScheduler for the platform will be
used.
Functions
fun LazyListPrefetchScope.onScroll(delta: Float, layoutInfo: LazyListLayoutInfo)
onScroll is invoked when the LazyList scrolls, whether or not the visible items have changed.
If the visible items have also changed, then this will be invoked in the same frame after
onVisibleItemsUpdated.
Parameters
| delta | the change in scroll direction. Delta < 0 indicates scrolling down while delta > 0 indicates scrolling up. |
| layoutInfo | the current LazyListLayoutInfo |
fun LazyListPrefetchScope.onVisibleItemsUpdated(layoutInfo: LazyListLayoutInfo)
onVisibleItemsUpdated is invoked when the LazyList scrolls if the visible items have changed.
Parameters
| layoutInfo | the current LazyListLayoutInfo. Info about the updated visible items can be found in LazyListLayoutInfo.visibleItemsInfo. |
fun NestedPrefetchScope.onNestedPrefetch(firstVisibleItemIndex: Int)
onNestedPrefetch is invoked when a parent LazyLayout has prefetched content which contains this LazyList. It gives this LazyList a chance to request prefetch for some of its own children before coming onto screen.
Implementations can use NestedPrefetchScope.schedulePrefetch to schedule child prefetches.
For example, this is useful if this LazyList is a LazyRow that is a child of a LazyColumn: in
that case, onNestedPrefetch can schedule the children it expects to be visible when it
comes onto screen, giving the LazyLayout infra a chance to compose these children ahead of
time and reduce jank.
Generally speaking, onNestedPrefetch should only request prefetch for children that it
expects to actually be visible when this list is scrolled into view.
Parameters
| firstVisibleItemIndex | the index of the first visible item. It should be used to start prefetching from the correct index in case the list has been created at a non-zero offset. |
