commonMain.androidx.compose.foundation.pager.PagerBeyondBoundsModifier.kt Maven / Gradle / Ivy

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Higher level abstractions of the Compose UI primitives. This library is design system agnostic, providing the high-level building blocks for both application and design-system developers

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/*
 * Copyright 2023 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.pager

import androidx.compose.foundation.lazy.layout.LazyLayoutBeyondBoundsState
import androidx.compose.runtime.Composable
import androidx.compose.runtime.remember

@Composable
internal fun rememberPagerBeyondBoundsState(
    state: PagerState,
    beyondViewportPageCount: Int
): LazyLayoutBeyondBoundsState {
    return remember(state, beyondViewportPageCount) {
        PagerBeyondBoundsState(state, beyondViewportPageCount)
    }
}

internal class PagerBeyondBoundsState(
    private val state: PagerState,
    private val beyondViewportPageCount: Int
) : LazyLayoutBeyondBoundsState {

    override val itemCount: Int
        get() = state.pageCount

    override val hasVisibleItems: Boolean
        get() = state.layoutInfo.visiblePagesInfo.isNotEmpty()

    override val firstPlacedIndex: Int
        get() = maxOf(0, state.firstVisiblePage - beyondViewportPageCount)

    override val lastPlacedIndex: Int
        get() =
            minOf(
                itemCount - 1,
                state.layoutInfo.visiblePagesInfo.last().index + beyondViewportPageCount
            )
}