LazyList.kt

/*
 * Copyright 2020 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.scrollable
import androidx.compose.foundation.layout.PaddingValues
import androidx.compose.foundation.layout.padding
import androidx.compose.runtime.Composable
import androidx.compose.runtime.remember
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.draw.clipToBounds
import androidx.compose.ui.gesture.scrollorientationlocking.Orientation
import androidx.compose.ui.layout.SubcomposeLayout
import androidx.compose.ui.platform.LayoutDirectionAmbient
import androidx.compose.ui.unit.LayoutDirection

@Composable
internal fun LazyList(
    itemsCount: Int,
    modifier: Modifier = Modifier,
    state: LazyListState,
    contentPadding: PaddingValues,
    horizontalAlignment: Alignment.Horizontal = Alignment.Start,
    verticalAlignment: Alignment.Vertical = Alignment.Top,
    isVertical: Boolean,
    itemContentFactory: LazyItemScope.(Int) -> @Composable () -> Unit
) {
    val reverseDirection = LayoutDirectionAmbient.current == LayoutDirection.Rtl && !isVertical

    val cachingItemContentFactory = remember { CachingItemContentFactory(itemContentFactory) }
    cachingItemContentFactory.itemContentFactory = itemContentFactory

    SubcomposeLayout<DataIndex>(
        modifier
            .scrollable(
                orientation = if (isVertical) Orientation.Vertical else Orientation.Horizontal,
                reverseDirection = reverseDirection,
                controller = state.scrollableController
            )
            .clipToBounds()
            .padding(contentPadding)
            .then(state.remeasurementModifier)
    ) { constraints ->
        // this will update the scope object if the constrains have been changed
        cachingItemContentFactory.updateItemScope(this, constraints)

        state.measure(
            this,
            constraints,
            isVertical,
            horizontalAlignment,
            verticalAlignment,
            itemsCount,
            cachingItemContentFactory
        )
    }
}