LazyListItemProvider.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.tv.foundation.lazy.list
import androidx.compose.foundation.ExperimentalFoundationApi
import androidx.compose.foundation.lazy.layout.LazyLayoutItemProvider
import androidx.compose.foundation.lazy.layout.PinnableItem
import androidx.compose.runtime.Composable
import androidx.compose.runtime.derivedStateOf
import androidx.compose.runtime.getValue
import androidx.compose.runtime.referentialEqualityPolicy
import androidx.compose.runtime.remember
import androidx.compose.runtime.rememberUpdatedState
import androidx.tv.foundation.lazy.layout.LazyLayoutKeyIndexMap
import androidx.tv.foundation.lazy.layout.NearestRangeKeyIndexMapState
@Suppress("IllegalExperimentalApiUsage") // TODO (b/233188423): Address before moving to beta
@ExperimentalFoundationApi
internal interface LazyListItemProvider : LazyLayoutItemProvider {
val keyToIndexMap: LazyLayoutKeyIndexMap
/** The list of indexes of the sticky header items */
val headerIndexes: List<Int>
/** The scope used by the item content lambdas */
val itemScope: TvLazyListItemScopeImpl
}
@OptIn(ExperimentalFoundationApi::class)
@Composable
internal fun rememberLazyListItemProvider(
state: TvLazyListState,
content: TvLazyListScope.() -> Unit
): LazyListItemProvider {
val latestContent = rememberUpdatedState(content)
return remember(state, latestContent) {
LazyListItemProviderImpl(
state = state,
latestContent = { latestContent.value },
itemScope = TvLazyListItemScopeImpl()
)
}
}
@ExperimentalFoundationApi
private class LazyListItemProviderImpl constructor(
private val state: TvLazyListState,
private val latestContent: () -> (TvLazyListScope.() -> Unit),
override val itemScope: TvLazyListItemScopeImpl
) : LazyListItemProvider {
private val listContent by derivedStateOf(referentialEqualityPolicy()) {
TvLazyListIntervalContent(latestContent())
}
override val itemCount: Int get() = listContent.itemCount
@Composable
override fun Item(index: Int) {
listContent.PinnableItem(index, state.pinnedItems) { localIndex ->
with(itemScope) { item(localIndex) }
}
}
override fun getKey(index: Int): Any = listContent.getKey(index)
override fun getContentType(index: Int): Any? = listContent.getContentType(index)
override val headerIndexes: List<Int> get() = listContent.headerIndexes
override val keyToIndexMap by NearestRangeKeyIndexMapState(
firstVisibleItemIndex = { state.firstVisibleItemIndex },
slidingWindowSize = { NearestItemsSlidingWindowSize },
extraItemCount = { NearestItemsExtraItemCount },
content = { listContent }
)
override fun getIndex(key: Any): Int = keyToIndexMap[key]
}
/**
* 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 = 30
/**
* The minimum amount of items near the current first visible item we want to have mapping for.
*/
private const val NearestItemsExtraItemCount = 100