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Pager: Bring back previous snapping behavior (#8776)

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New default LazyList snap behavior is optimized for non-pager use.
This commit is contained in:
Ivan Iskandar 2022-12-20 21:16:43 +07:00 committed by GitHub
parent 8552838bda
commit 8e1b5b4803
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GPG key ID: 4AEE18F83AFDEB23
1 changed files with 79 additions and 2 deletions
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81
app/src/main/java/eu/kanade/presentation/components/Pager.kt
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@ -1,5 +1,8 @@
package eu.kanade.presentation.components
import androidx.compose.foundation.gestures.FlingBehavior
import androidx.compose.foundation.gestures.Orientation
import androidx.compose.foundation.gestures.snapping.SnapLayoutInfoProvider
import androidx.compose.foundation.gestures.snapping.rememberSnapFlingBehavior
import androidx.compose.foundation.layout.Arrangement
import androidx.compose.foundation.layout.Box
@ -7,6 +10,7 @@ import androidx.compose.foundation.layout.BoxScope
import androidx.compose.foundation.layout.PaddingValues
import androidx.compose.foundation.layout.wrapContentSize
import androidx.compose.foundation.lazy.LazyListItemInfo
import androidx.compose.foundation.lazy.LazyListLayoutInfo
import androidx.compose.foundation.lazy.LazyListState
import androidx.compose.foundation.lazy.LazyRow
import androidx.compose.runtime.Composable
@ -14,6 +18,7 @@ import androidx.compose.runtime.LaunchedEffect
import androidx.compose.runtime.Stable
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.saveable.Saver
import androidx.compose.runtime.saveable.listSaver
import androidx.compose.runtime.saveable.rememberSaveable
@ -21,7 +26,10 @@ import androidx.compose.runtime.setValue
import androidx.compose.runtime.snapshotFlow
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.unit.Density
import androidx.compose.ui.util.fastForEach
import androidx.compose.ui.util.fastMaxBy
import androidx.compose.ui.util.fastSumBy
import kotlinx.coroutines.flow.distinctUntilChanged
@Composable
@ -79,7 +87,7 @@ private fun Pager(
horizontalAlignment = horizontalAlignment,
verticalArrangement = Arrangement.aligned(verticalAlignment),
userScrollEnabled = userScrollEnabled,
flingBehavior = rememberSnapFlingBehavior(lazyListState = state.lazyListState),
flingBehavior = rememberLazyListSnapFlingBehavior(lazyListState = state.lazyListState),
) {
items(
count = count,
@ -102,7 +110,7 @@ private fun Pager(
verticalAlignment = verticalAlignment,
horizontalArrangement = Arrangement.aligned(horizontalAlignment),
userScrollEnabled = userScrollEnabled,
flingBehavior = rememberSnapFlingBehavior(lazyListState = state.lazyListState),
flingBehavior = rememberLazyListSnapFlingBehavior(lazyListState = state.lazyListState),
) {
items(
count = count,
@ -180,3 +188,72 @@ class PagerState(
)
}
}
// https://android.googlesource.com/platform/frameworks/support/+/refs/changes/78/2160778/35/compose/foundation/foundation/src/commonMain/kotlin/androidx/compose/foundation/gestures/snapping/LazyListSnapLayoutInfoProvider.kt
private fun lazyListSnapLayoutInfoProvider(
lazyListState: LazyListState,
positionInLayout: (layoutSize: Float, itemSize: Float) -> Float = { layoutSize, itemSize ->
layoutSize / 2f - itemSize / 2f
},
) = object : SnapLayoutInfoProvider {
private val layoutInfo: LazyListLayoutInfo
get() = lazyListState.layoutInfo
// Single page snapping is the default
override fun Density.calculateApproachOffset(initialVelocity: Float): Float = 0f
override fun Density.calculateSnappingOffsetBounds(): ClosedFloatingPointRange<Float> {
var lowerBoundOffset = Float.NEGATIVE_INFINITY
var upperBoundOffset = Float.POSITIVE_INFINITY
layoutInfo.visibleItemsInfo.fastForEach { item ->
val offset =
calculateDistanceToDesiredSnapPosition(layoutInfo, item, positionInLayout)
// Find item that is closest to the center
if (offset <= 0 && offset > lowerBoundOffset) {
lowerBoundOffset = offset
}
// Find item that is closest to center, but after it
if (offset >= 0 && offset < upperBoundOffset) {
upperBoundOffset = offset
}
}
return lowerBoundOffset.rangeTo(upperBoundOffset)
}
override fun Density.calculateSnapStepSize(): Float = with(layoutInfo) {
if (visibleItemsInfo.isNotEmpty()) {
visibleItemsInfo.fastSumBy { it.size } / visibleItemsInfo.size.toFloat()
} else {
0f
}
}
}
@Composable
private fun rememberLazyListSnapFlingBehavior(lazyListState: LazyListState): FlingBehavior {
val snappingLayout = remember(lazyListState) { lazyListSnapLayoutInfoProvider(lazyListState) }
return rememberSnapFlingBehavior(snappingLayout)
}
private fun calculateDistanceToDesiredSnapPosition(
layoutInfo: LazyListLayoutInfo,
item: LazyListItemInfo,
positionInLayout: (layoutSize: Float, itemSize: Float) -> Float,
): Float {
val containerSize =
with(layoutInfo) { singleAxisViewportSize - beforeContentPadding - afterContentPadding }
val desiredDistance =
positionInLayout(containerSize.toFloat(), item.size.toFloat())
val itemCurrentPosition = item.offset
return itemCurrentPosition - desiredDistance
}
private val LazyListLayoutInfo.singleAxisViewportSize: Int
get() = if (orientation == Orientation.Vertical) viewportSize.height else viewportSize.width