commonMain.androidx.compose.foundation.lazy.layout.LazyLayoutPrefetchState.kt Maven / Gradle / Ivy

Go to download
/*
 * 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.compose.foundation.lazy.layout

import androidx.compose.foundation.ExperimentalFoundationApi
import androidx.compose.runtime.Stable
import androidx.compose.ui.unit.Constraints

/**
 * State for lazy items prefetching, used by lazy layouts to instruct the prefetcher.
 */
@ExperimentalFoundationApi
@Stable
class LazyLayoutPrefetchState {
    internal var prefetcher: Prefetcher? = null

    /**
     * Schedules precomposition and premeasure for the new item.
     *
     * @param index item index to prefetch.
     * @param constraints [Constraints] to use for premeasuring.
     */
    fun schedulePrefetch(index: Int, constraints: Constraints): PrefetchHandle {
        return prefetcher?.schedulePrefetch(index, constraints) ?: DummyHandle
    }

    sealed interface PrefetchHandle {
        /**
         * Notifies the prefetcher that previously scheduled item is no longer needed. If the item
         * was precomposed already it will be disposed.
         */
        fun cancel()
    }

    internal interface Prefetcher {
        fun schedulePrefetch(index: Int, constraints: Constraints): PrefetchHandle
    }
}

@ExperimentalFoundationApi
private object DummyHandle : LazyLayoutPrefetchState.PrefetchHandle {
    override fun cancel() {}
}