LazyStaggeredGridItemProvider.kt
/*
* Copyright 2022 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.staggeredgrid
import androidx.compose.foundation.ExperimentalFoundationApi
import androidx.compose.foundation.lazy.layout.LazyLayoutItemProvider
import androidx.compose.foundation.lazy.layout.LazyLayoutKeyIndexMap
import androidx.compose.foundation.lazy.layout.PinnableItem
import androidx.compose.foundation.lazy.layout.NearestRangeKeyIndexMapState
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
@OptIn(ExperimentalFoundationApi::class)
internal interface LazyStaggeredGridItemProvider : LazyLayoutItemProvider {
val spanProvider: LazyStaggeredGridSpanProvider
val keyToIndexMap: LazyLayoutKeyIndexMap
}
@Composable
internal fun rememberStaggeredGridItemProvider(
state: LazyStaggeredGridState,
content: LazyStaggeredGridScope.() -> Unit,
): LazyStaggeredGridItemProvider {
val latestContent = rememberUpdatedState(content)
return remember(state) {
LazyStaggeredGridItemProviderImpl(
state,
{ latestContent.value },
)
}
}
@OptIn(ExperimentalFoundationApi::class)
private class LazyStaggeredGridItemProviderImpl(
private val state: LazyStaggeredGridState,
private val latestContent: () -> (LazyStaggeredGridScope.() -> Unit)
) : LazyStaggeredGridItemProvider {
private val staggeredGridContent by derivedStateOf(referentialEqualityPolicy()) {
LazyStaggeredGridIntervalContent(latestContent())
}
override val keyToIndexMap: LazyLayoutKeyIndexMap by NearestRangeKeyIndexMapState(
firstVisibleItemIndex = { state.firstVisibleItemIndex },
slidingWindowSize = { 90 },
extraItemCount = { 200 },
content = { staggeredGridContent }
)
override val itemCount: Int get() = staggeredGridContent.itemCount
override fun getKey(index: Int): Any = staggeredGridContent.getKey(index)
override fun getIndex(key: Any): Int = keyToIndexMap[key]
override fun getContentType(index: Int): Any? = staggeredGridContent.getContentType(index)
@Composable
override fun Item(index: Int) {
staggeredGridContent.PinnableItem(index, state.pinnedItems) { localIndex ->
with(LazyStaggeredGridItemScopeImpl) {
item(localIndex)
}
}
}
override val spanProvider get() = staggeredGridContent.spanProvider
}