LazyStaggeredGrid.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.staggeredgrid
import androidx.compose.foundation.ExperimentalFoundationApi
import androidx.compose.foundation.clipScrollableContainer
import androidx.compose.foundation.gestures.FlingBehavior
import androidx.compose.foundation.gestures.Orientation
import androidx.compose.foundation.gestures.ScrollableDefaults
import androidx.compose.foundation.gestures.scrollable
import androidx.compose.foundation.layout.Arrangement
import androidx.compose.foundation.layout.PaddingValues
import androidx.compose.foundation.lazy.layout.LazyLayout
import androidx.compose.foundation.lazy.layout.LazyLayoutItemProvider
import androidx.compose.foundation.lazy.layout.lazyLayoutSemantics
import androidx.compose.foundation.overscroll
import androidx.compose.runtime.Composable
import androidx.compose.ui.Modifier
import androidx.compose.ui.platform.LocalLayoutDirection
import androidx.compose.ui.unit.Constraints
import androidx.compose.ui.unit.Density
import androidx.compose.ui.unit.dp
@ExperimentalFoundationApi
@Composable
internal fun LazyStaggeredGrid(
/** State controlling the scroll position */
state: LazyStaggeredGridState,
/** The layout orientation of the grid */
orientation: Orientation,
/** Prefix sums of cross axis sizes of slots per line, e.g. the columns for vertical grid. */
slotSizesSums: Density.(Constraints) -> IntArray,
/** Modifier to be applied for the inner layout */
modifier: Modifier = Modifier,
/** The inner padding to be added for the whole content (not for each individual item) */
contentPadding: PaddingValues = PaddingValues(0.dp),
/** reverse the direction of scrolling and layout */
reverseLayout: Boolean = false,
/** fling behavior to be used for flinging */
flingBehavior: FlingBehavior = ScrollableDefaults.flingBehavior(),
/** Whether scrolling via the user gestures is allowed. */
userScrollEnabled: Boolean = true,
/** The vertical arrangement for items/lines. */
verticalArrangement: Arrangement.Vertical = Arrangement.Top,
/** The horizontal arrangement for items/lines. */
horizontalArrangement: Arrangement.Horizontal = Arrangement.Start,
/** The content of the grid */
content: LazyStaggeredGridScope.() -> Unit
) {
val overscrollEffect = ScrollableDefaults.overscrollEffect()
val itemProvider = rememberStaggeredGridItemProvider(state, content)
val measurePolicy = rememberStaggeredGridMeasurePolicy(
state,
itemProvider,
contentPadding,
reverseLayout,
orientation,
verticalArrangement,
horizontalArrangement,
slotSizesSums,
overscrollEffect
)
val semanticState = rememberLazyStaggeredGridSemanticState(state, itemProvider, reverseLayout)
ScrollPositionUpdater(itemProvider, state)
LazyLayout(
modifier = modifier
.then(state.remeasurementModifier)
.clipScrollableContainer(orientation)
.overscroll(overscrollEffect)
.scrollable(
orientation = orientation,
reverseDirection = ScrollableDefaults.reverseDirection(
LocalLayoutDirection.current,
orientation,
reverseLayout
),
interactionSource = state.mutableInteractionSource,
flingBehavior = flingBehavior,
state = state,
overscrollEffect = overscrollEffect,
enabled = userScrollEnabled
)
.lazyLayoutSemantics(
itemProvider = itemProvider,
state = semanticState,
orientation = orientation,
userScrollEnabled = userScrollEnabled
),
prefetchState = state.prefetchState,
itemProvider = itemProvider,
measurePolicy = measurePolicy
)
}
/** Extracted to minimize the recomposition scope */
@OptIn(ExperimentalFoundationApi::class)
@Composable
private fun ScrollPositionUpdater(
itemProvider: LazyLayoutItemProvider,
state: LazyStaggeredGridState
) {
if (itemProvider.itemCount > 0) {
state.updateScrollPositionIfTheFirstItemWasMoved(itemProvider)
}
}