LazySemantics.kt
/*
* 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.list
import androidx.compose.foundation.gestures.ScrollableState
import androidx.compose.foundation.gestures.animateScrollBy
import androidx.compose.foundation.lazy.LazyListState
import androidx.compose.runtime.State
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.CoroutineScope
import kotlinx.coroutines.launch
internal fun Modifier.lazyListSemantics(
stateOfItemsProvider: State<LazyListItemsProvider>,
state: LazyListState,
coroutineScope: CoroutineScope,
isVertical: Boolean,
reverseScrolling: Boolean
): Modifier {
return semantics {
indexForKey { needle ->
val key = stateOfItemsProvider.value::getKey
for (index in 0 until stateOfItemsProvider.value.itemsCount) {
if (key(index) == needle) {
return@indexForKey index
}
}
-1
}
val accessibilityScrollState = ScrollAxisRange(
value = {
// This is a simple way of representing the current position without
// needing any lazy items to be measured. It's good enough so far, because
// screen-readers care mostly about whether scroll position changed or not
// rather than the actual offset in pixels.
state.firstVisibleItemIndex + state.firstVisibleItemScrollOffset / 100_000f
},
maxValue = {
if (state.canScrollForward) {
// If we can scroll further, we don't know the end yet,
// but it's upper bounded by #items + 1
stateOfItemsProvider.value.itemsCount + 1f
} else {
// If we can't scroll further, the current value is the max
state.firstVisibleItemIndex + state.firstVisibleItemScrollOffset / 100_000f
}
},
reverseScrolling = reverseScrolling
)
if (isVertical) {
verticalScrollAxisRange = accessibilityScrollState
} else {
horizontalScrollAxisRange = accessibilityScrollState
}
scrollBy { x, y ->
val delta = if (isVertical) { y } else { x }
coroutineScope.launch {
(state as ScrollableState).animateScrollBy(delta)
}
// TODO(aelias): is it important to return false if we know in advance we cannot scroll?
true
}
scrollToIndex { index ->
require(index >= 0 && index < state.layoutInfo.totalItemsCount) {
"Can't scroll to index $index, it is out of " +
"bounds [0, ${state.layoutInfo.totalItemsCount})"
}
coroutineScope.launch {
state.scrollToItem(index)
}
true
}
collectionInfo = CollectionInfo(
rowCount = if (isVertical) -1 else 1,
columnCount = if (isVertical) 1 else -1
)
}
}