LazyLayoutSemantics.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.layout
import androidx.compose.foundation.ExperimentalFoundationApi
import androidx.compose.foundation.gestures.Orientation
import androidx.compose.foundation.gestures.animateScrollBy
import androidx.compose.runtime.Composable
import androidx.compose.runtime.remember
import androidx.compose.runtime.rememberCoroutineScope
import androidx.compose.ui.Modifier
import androidx.compose.ui.semantics.CollectionInfo
import androidx.compose.ui.semantics.ScrollAxisRange
import androidx.compose.ui.semantics.collectionInfo
import androidx.compose.ui.semantics.horizontalScrollAxisRange
import androidx.compose.ui.semantics.indexForKey
import androidx.compose.ui.semantics.scrollBy
import androidx.compose.ui.semantics.scrollToIndex
import androidx.compose.ui.semantics.semantics
import androidx.compose.ui.semantics.verticalScrollAxisRange
import kotlinx.coroutines.launch
@OptIn(ExperimentalFoundationApi::class)
@Suppress("ComposableModifierFactory", "ModifierInspectorInfo")
@Composable
internal fun Modifier.lazyLayoutSemantics(
itemProvider: LazyLayoutItemProvider,
state: LazyLayoutSemanticState,
orientation: Orientation,
userScrollEnabled: Boolean
): Modifier {
val coroutineScope = rememberCoroutineScope()
return this.then(
remember(
itemProvider,
state,
orientation,
userScrollEnabled
) {
val isVertical = orientation == Orientation.Vertical
val indexForKeyMapping: (Any) -> Int = { needle ->
var result = -1
for (index in 0 until itemProvider.itemCount) {
if (itemProvider.getKey(index) == needle) {
result = index
break
}
}
result
}
val accessibilityScrollState = state.scrollAxisRange()
val scrollByAction: ((x: Float, y: Float) -> Boolean)? = if (userScrollEnabled) {
{ x, y ->
val delta = if (isVertical) {
y
} else {
x
}
coroutineScope.launch {
state.animateScrollBy(delta)
}
// TODO(aelias): is it important to return false if we know in advance we cannot scroll?
true
}
} else {
null
}
val scrollToIndexAction: ((Int) -> Boolean)? = if (userScrollEnabled) {
{ index ->
require(index >= 0 && index < itemProvider.itemCount) {
"Can't scroll to index $index, it is out of " +
"bounds [0, ${itemProvider.itemCount})"
}
coroutineScope.launch {
state.scrollToItem(index)
}
true
}
} else {
null
}
val collectionInfo = state.collectionInfo()
Modifier.semantics {
indexForKey(indexForKeyMapping)
if (isVertical) {
verticalScrollAxisRange = accessibilityScrollState
} else {
horizontalScrollAxisRange = accessibilityScrollState
}
if (scrollByAction != null) {
scrollBy(action = scrollByAction)
}
if (scrollToIndexAction != null) {
scrollToIndex(action = scrollToIndexAction)
}
this.collectionInfo = collectionInfo
}
}
)
}
internal interface LazyLayoutSemanticState {
fun scrollAxisRange(): ScrollAxisRange
fun collectionInfo(): CollectionInfo
suspend fun animateScrollBy(delta: Float)
suspend fun scrollToItem(index: Int)
}