LazyListPinningModifier.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
import androidx.compose.foundation.ExperimentalFoundationApi
import androidx.compose.foundation.lazy.layout.ModifierLocalPinnableParent
import androidx.compose.foundation.lazy.layout.PinnableParent
import androidx.compose.runtime.Composable
import androidx.compose.runtime.remember
import androidx.compose.ui.Modifier
import androidx.compose.ui.modifier.ModifierLocalConsumer
import androidx.compose.ui.modifier.ModifierLocalProvider
import androidx.compose.ui.modifier.ModifierLocalReadScope
import androidx.compose.ui.modifier.ProvidableModifierLocal
/**
* This is a temporary placeholder implementation of pinning until we implement b/195049010.
*/
@Suppress("ComposableModifierFactory")
@Composable
internal fun Modifier.lazyListPinningModifier(
state: LazyListState,
beyondBoundsInfo: LazyListBeyondBoundsInfo
): Modifier {
return this then remember(state, beyondBoundsInfo) {
LazyListPinningModifier(state, beyondBoundsInfo)
}
}
@OptIn(ExperimentalFoundationApi::class)
private class LazyListPinningModifier(
private val state: LazyListState,
private val beyondBoundsInfo: LazyListBeyondBoundsInfo,
) : ModifierLocalProvider<PinnableParent?>, ModifierLocalConsumer, PinnableParent {
var pinnableGrandParent: PinnableParent? = null
override val key: ProvidableModifierLocal<PinnableParent?>
get() = ModifierLocalPinnableParent
override val value: PinnableParent
get() = this
override fun onModifierLocalsUpdated(scope: ModifierLocalReadScope) {
pinnableGrandParent = with(scope) { ModifierLocalPinnableParent.current }
}
override fun pinItems(): PinnableParent.PinnedItemsHandle = with(beyondBoundsInfo) {
if (hasIntervals()) {
object : PinnableParent.PinnedItemsHandle {
val parentPinnedItemsHandle = pinnableGrandParent?.pinItems()
val interval = addInterval(start, end)
override fun unpin() {
removeInterval(interval)
parentPinnedItemsHandle?.unpin()
state.remeasurement?.forceRemeasure()
}
}
} else {
pinnableGrandParent?.pinItems() ?: EmptyPinnedItemsHandle
}
}
companion object {
private val EmptyPinnedItemsHandle = object : PinnableParent.PinnedItemsHandle {
override fun unpin() {}
}
}
}