/
PagerTab.kt
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/
PagerTab.kt
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/*
* 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
*
* https://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 com.google.accompanist.pager
import androidx.compose.material.ScrollableTabRow
import androidx.compose.material.TabPosition
import androidx.compose.material.TabRow
import androidx.compose.ui.Modifier
import androidx.compose.ui.layout.layout
import androidx.compose.ui.unit.Constraints
import androidx.compose.ui.unit.lerp
/**
* This indicator syncs up a [TabRow] or [ScrollableTabRow] tab indicator with a
* [HorizontalPager] or [VerticalPager]. See the sample for a full demonstration.
*
* @sample com.google.accompanist.sample.pager.PagerWithTabs
*/
@ExperimentalPagerApi
fun Modifier.pagerTabIndicatorOffset(
pagerState: PagerState,
tabPositions: List<TabPosition>,
pageIndexMapping: (Int) -> Int = { it },
): Modifier = layout { measurable, constraints ->
if (tabPositions.isEmpty()) {
// If there are no pages, nothing to show
layout(constraints.maxWidth, 0) {}
} else {
val currentPage = minOf(tabPositions.lastIndex, pageIndexMapping(pagerState.currentPage))
val currentTab = tabPositions[currentPage]
val previousTab = tabPositions.getOrNull(currentPage - 1)
val nextTab = tabPositions.getOrNull(currentPage + 1)
val fraction = pagerState.currentPageOffset
val indicatorWidth = if (fraction > 0 && nextTab != null) {
lerp(currentTab.width, nextTab.width, fraction).roundToPx()
} else if (fraction < 0 && previousTab != null) {
lerp(currentTab.width, previousTab.width, -fraction).roundToPx()
} else {
currentTab.width.roundToPx()
}
val indicatorOffset = if (fraction > 0 && nextTab != null) {
lerp(currentTab.left, nextTab.left, fraction).roundToPx()
} else if (fraction < 0 && previousTab != null) {
lerp(currentTab.left, previousTab.left, -fraction).roundToPx()
} else {
currentTab.left.roundToPx()
}
val placeable = measurable.measure(
Constraints(
minWidth = indicatorWidth,
maxWidth = indicatorWidth,
minHeight = 0,
maxHeight = constraints.maxHeight
)
)
layout(constraints.maxWidth, maxOf(placeable.height, constraints.minHeight)) {
placeable.place(
indicatorOffset,
maxOf(constraints.minHeight - placeable.height, 0)
)
}
}
}