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.tv.foundation.lazy.grid
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 LazyGridItemProvider : LazyLayoutItemProvider {
val spanLayoutProvider: LazyGridSpanLayoutProvider
val keyToIndexMap: LazyLayoutKeyIndexMap
}
@ExperimentalFoundationApi
@Composable
internal fun rememberLazyGridItemProvider(
state: TvLazyGridState,
content: TvLazyGridScope.() -> Unit,
): LazyGridItemProvider {
val latestContent = rememberUpdatedState(content)
return remember(state) {
LazyGridItemProviderImpl(
state,
{ latestContent.value },
)
}
}
@ExperimentalFoundationApi
private class LazyGridItemProviderImpl(
private val state: TvLazyGridState,
private val latestContent: () -> (TvLazyGridScope.() -> Unit)
) : LazyGridItemProvider {
private val gridContent by derivedStateOf(referentialEqualityPolicy()) {
LazyGridIntervalContent(latestContent())
}
override val itemCount: Int get() = gridContent.itemCount
override fun getKey(index: Int): Any = gridContent.getKey(index)
override fun getContentType(index: Int): Any? = gridContent.getContentType(index)
@Composable
override fun Item(index: Int) {
gridContent.PinnableItem(index, state.pinnedItems) { localIndex ->
with(TvLazyGridItemScopeImpl) {
item(localIndex)
}
}
}
override val spanLayoutProvider: LazyGridSpanLayoutProvider
get() = gridContent.spanLayoutProvider
override val keyToIndexMap: LazyLayoutKeyIndexMap by NearestRangeKeyIndexMapState(
firstVisibleItemIndex = { state.firstVisibleItemIndex },
slidingWindowSize = { NearestItemsSlidingWindowSize },
extraItemCount = { NearestItemsExtraItemCount },
content = { gridContent }
)
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 = 90
/**
* The minimum amount of items near the current first visible item we want to have mapping for.
*/
private const val NearestItemsExtraItemCount = 200