LazyGridItemProvider.kt
/*
* Copyright 2021 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package androidx.compose.foundation.lazy.grid
import androidx.compose.foundation.ExperimentalFoundationApi
import androidx.compose.foundation.lazy.layout.DelegatingLazyLayoutItemProvider
import androidx.compose.foundation.lazy.layout.IntervalList
import androidx.compose.foundation.lazy.layout.LazyLayoutItemProvider
import androidx.compose.foundation.lazy.layout.rememberLazyNearestItemsRangeState
import androidx.compose.runtime.Composable
import androidx.compose.runtime.State
import androidx.compose.runtime.derivedStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.rememberUpdatedState
@ExperimentalFoundationApi
internal interface LazyGridItemProvider : LazyLayoutItemProvider {
val spanLayoutProvider: LazyGridSpanLayoutProvider
val hasCustomSpans: Boolean
fun LazyGridItemSpanScope.getSpan(index: Int): GridItemSpan
}
@ExperimentalFoundationApi
@Composable
internal fun rememberLazyGridItemProvider(
state: LazyGridState,
content: LazyGridScope.() -> Unit,
): LazyGridItemProvider {
val latestContent = rememberUpdatedState(content)
val nearestItemsRangeState = rememberLazyNearestItemsRangeState(
firstVisibleItemIndex = remember(state) {
{ state.firstVisibleItemIndex }
},
slidingWindowSize = { NearestItemsSlidingWindowSize },
extraItemCount = { NearestItemsExtraItemCount }
)
return remember(nearestItemsRangeState) {
val itemProviderState: State<LazyGridItemProvider> = derivedStateOf {
val gridScope = LazyGridScopeImpl().apply(latestContent.value)
LazyGridItemProviderImpl(
gridScope.intervals,
gridScope.hasCustomSpans,
nearestItemsRangeState.value
)
}
object : LazyGridItemProvider,
LazyLayoutItemProvider by DelegatingLazyLayoutItemProvider(itemProviderState) {
override val spanLayoutProvider: LazyGridSpanLayoutProvider
get() = itemProviderState.value.spanLayoutProvider
override val hasCustomSpans: Boolean
get() = itemProviderState.value.hasCustomSpans
override fun LazyGridItemSpanScope.getSpan(index: Int): GridItemSpan =
with(itemProviderState.value) {
getSpan(index)
}
}
}
}
@ExperimentalFoundationApi
private class LazyGridItemProviderImpl(
private val intervals: IntervalList<LazyGridIntervalContent>,
override val hasCustomSpans: Boolean,
nearestItemsRange: IntRange
) : LazyGridItemProvider, LazyLayoutItemProvider by LazyLayoutItemProvider(
intervals = intervals,
nearestItemsRange = nearestItemsRange,
itemContent = { interval, index ->
interval.item.invoke(LazyGridItemScopeImpl, index)
}
) {
override val spanLayoutProvider: LazyGridSpanLayoutProvider =
LazyGridSpanLayoutProvider(this)
override fun LazyGridItemSpanScope.getSpan(index: Int): GridItemSpan {
val interval = intervals[index]
val localIntervalIndex = index - interval.startIndex
return interval.value.span.invoke(this, localIntervalIndex)
}
}
/**
* We use the idea of sliding window as an optimization, so user can scroll up to this number of
* items until we have to regenerate the key to index map.
*/
private const val NearestItemsSlidingWindowSize = 90
/**
* The minimum amount of items near the current first visible item we want to have mapping for.
*/
private const val NearestItemsExtraItemCount = 200