LazyListBeyondBoundsModifier.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.gestures.Orientation
import androidx.compose.foundation.lazy.layout.BeyondBoundsState
import androidx.compose.foundation.lazy.layout.LazyLayoutBeyondBoundsModifierLocal
import androidx.compose.runtime.Composable
import androidx.compose.runtime.remember
import androidx.compose.ui.Modifier
import androidx.compose.ui.platform.LocalLayoutDirection
/**
* This modifier is used to measure and place additional items when the lazyList receives a
* request to layout items beyond the visible bounds.
*/
@Suppress("ComposableModifierFactory")
@Composable
internal fun Modifier.lazyListBeyondBoundsModifier(
state: LazyListState,
beyondBoundsInfo: LazyListBeyondBoundsInfo,
reverseLayout: Boolean,
orientation: Orientation
): Modifier {
val layoutDirection = LocalLayoutDirection.current
val beyondBoundsState = remember(state) { LazyListBeyondBoundsState(state) }
return this then remember(
beyondBoundsState,
beyondBoundsInfo,
reverseLayout,
layoutDirection,
orientation
) {
LazyLayoutBeyondBoundsModifierLocal(
beyondBoundsState,
beyondBoundsInfo,
reverseLayout,
layoutDirection,
orientation
)
}
}
internal class LazyListBeyondBoundsState(val state: LazyListState) : BeyondBoundsState {
override fun remeasure() {
state.remeasurement?.forceRemeasure()
}
override val itemCount: Int
get() = state.layoutInfo.totalItemsCount
override val hasVisibleItems: Boolean
get() = state.layoutInfo.visibleItemsInfo.isNotEmpty()
override val firstVisibleIndex: Int
get() = state.firstVisibleItemIndex
override val lastVisibleIndex: Int
get() = state.layoutInfo.visibleItemsInfo.last().index
}