alexandrosla
commented
5 years ago Same problem here!
Until we have a proper fix for this issue, you could use a CustomTabLayoutMediator instead, and check tabLayout.getTabAt(currItem)?.select()
below you can find a full CustomTabLayoutMediator in Kotlin.
import androidx.recyclerview.widget.RecyclerView
import androidx.viewpager2.widget.ViewPager2
import androidx.viewpager2.widget.ViewPager2.*
import com.google.android.material.tabs.TabLayout
import java.lang.ref.WeakReference
class CustomTabLayoutMediator(
private val tabLayout: TabLayout,
private val viewPager: ViewPager2,
private val autoRefresh: Boolean,
private val tabConfigurationStrategy: TabConfigurationStrategy
) {
private var adapter: RecyclerView.Adapter<*>? = null
private var attached: Boolean = false
private var onPageChangeCallback: TabLayoutOnPageChangeCallback? = null
private var onTabSelectedListener: TabLayout.OnTabSelectedListener? = null
private var pagerAdapterObserver: RecyclerView.AdapterDataObserver? = null
/**
* A callback interface that must be implemented to set the text and styling of newly created
* tabs.
*/
interface TabConfigurationStrategy {
/**
* Called to configure the tab for the page at the specified position. Typically calls [ ][TabLayout.Tab.setText], but any form of styling can be applied.
*
* @param tab The Tab which should be configured to represent the title of the item at the given
* position in the data set.
* @param position The position of the item within the adapter's data set.
*/
fun onConfigureTab(tab: TabLayout.Tab, position: Int)
}
constructor(
tabLayout: TabLayout,
viewPager: ViewPager2,
tabConfigurationStrategy: TabConfigurationStrategy
) : this(tabLayout, viewPager, true, tabConfigurationStrategy) {
}
/**
* Link the TabLayout and the ViewPager2 together. Must be called after ViewPager2 has an adapter
* set. To be called on a new instance of TabLayoutMediator or if the ViewPager2's adapter
* changes.
*
* @throws IllegalStateException If the mediator is already attached, or the ViewPager2 has no
* adapter.
*/
fun attach() {
check(!attached) { "TabLayoutMediator is already attached" }
adapter = viewPager.adapter
checkNotNull(adapter) { "TabLayoutMediator attached before ViewPager2 has an " + "adapter" }
attached = true
// Add our custom OnPageChangeCallback to the ViewPager
onPageChangeCallback = TabLayoutOnPageChangeCallback(tabLayout).apply {
viewPager.registerOnPageChangeCallback(this)
}
// Now we'll add a tab selected listener to set ViewPager's current item
onTabSelectedListener = ViewPagerOnTabSelectedListener(viewPager).apply {
tabLayout.addOnTabSelectedListener(this)
}
// Now we'll populate ourselves from the pager adapter, adding an observer if
// autoRefresh is enabled
if (autoRefresh) {
// Register our observer on the new adapter
pagerAdapterObserver = PagerAdapterObserver().apply {
adapter?.registerAdapterDataObserver(this)
}
}
populateTabsFromPagerAdapter()
// Now update the scroll position to match the ViewPager's current item
tabLayout.setScrollPosition(viewPager.currentItem, 0f, true)
}
/**
* Unlink the TabLayout and the ViewPager. To be called on a stale TabLayoutMediator if a new one
* is instantiated, to prevent holding on to a view that should be garbage collected. Also to be
* called before [.attach] when a ViewPager2's adapter is changed.
*/
fun detach() {
pagerAdapterObserver?.let {
adapter?.unregisterAdapterDataObserver(it)
}
onTabSelectedListener?.let {
tabLayout.removeOnTabSelectedListener(it)
}
onPageChangeCallback?.let {
viewPager.unregisterOnPageChangeCallback(it)
}
pagerAdapterObserver = null
onTabSelectedListener = null
onPageChangeCallback = null
adapter = null
attached = false
}
internal fun populateTabsFromPagerAdapter() {
tabLayout.removeAllTabs()
adapter?.itemCount?.let { adapterCount ->
for (i in 0 until adapterCount) {
val tab = tabLayout.newTab()
tabConfigurationStrategy.onConfigureTab(tab, i)
tabLayout.addTab(tab, false)
}
// Make sure we reflect the currently set ViewPager item
if (adapterCount > 0) {
val currItem = viewPager.currentItem
if (currItem != tabLayout.selectedTabPosition) {
tabLayout.getTabAt(currItem)?.select()
}
}
}
}
/**
* A [ViewPager2.OnPageChangeCallback] class which contains the necessary calls back to the
* provided [TabLayout] so that the tab position is kept in sync.
*
*
* This class stores the provided TabLayout weakly, meaning that you can use [ ][ViewPager2.registerOnPageChangeCallback] without removing the
* callback and not cause a leak.
*/
private class TabLayoutOnPageChangeCallback internal constructor(tabLayout: TabLayout) :
ViewPager2.OnPageChangeCallback() {
private val tabLayoutRef: WeakReference<TabLayout>
private var previousScrollState: Int = 0
private var scrollState: Int = 0
init {
tabLayoutRef = WeakReference(tabLayout)
reset()
}
override fun onPageScrollStateChanged(state: Int) {
previousScrollState = scrollState
scrollState = state
}
override fun onPageScrolled(
position: Int,
positionOffset: Float,
positionOffsetPixels: Int
) {
tabLayoutRef.get()?.let { tabLayout ->
// Only update the text selection if we're not settling, or we are settling after
// being dragged
val updateText =
scrollState != SCROLL_STATE_SETTLING || previousScrollState == SCROLL_STATE_DRAGGING
// Update the indicator if we're not settling after being idle. This is caused
// from a setCurrentItem() call and will be handled by an animation from
// onPageSelected() instead.
val updateIndicator =
!(scrollState == SCROLL_STATE_SETTLING && previousScrollState == SCROLL_STATE_IDLE)
tabLayout.setScrollPosition(position, positionOffset, updateText, updateIndicator)
}
}
override fun onPageSelected(position: Int) {
tabLayoutRef.get()?.let { tabLayout ->
if (tabLayout.selectedTabPosition != position
&& position < tabLayout.tabCount
) {
// Select the tab, only updating the indicator if we're not being dragged/settled
// (since onPageScrolled will handle that).
val updateIndicator =
scrollState == SCROLL_STATE_IDLE || scrollState == SCROLL_STATE_SETTLING && previousScrollState == SCROLL_STATE_IDLE
tabLayout.selectTab(tabLayout.getTabAt(position), updateIndicator)
}
}
}
internal fun reset() {
scrollState = SCROLL_STATE_IDLE
previousScrollState = scrollState
}
}
/**
* A [TabLayout.OnTabSelectedListener] class which contains the necessary calls back to the
* provided [ViewPager2] so that the tab position is kept in sync.
*/
private class ViewPagerOnTabSelectedListener internal constructor(private val viewPager: ViewPager2) :
TabLayout.OnTabSelectedListener {
override fun onTabSelected(tab: TabLayout.Tab) {
viewPager.setCurrentItem(tab.position, true)
}
override fun onTabUnselected(tab: TabLayout.Tab) {
// No-op
}
override fun onTabReselected(tab: TabLayout.Tab) {
// No-op
}
}
private inner class PagerAdapterObserver internal constructor() :
RecyclerView.AdapterDataObserver() {
override fun onChanged() {
populateTabsFromPagerAdapter()
}
override fun onItemRangeChanged(positionStart: Int, itemCount: Int) {
populateTabsFromPagerAdapter()
}
override fun onItemRangeChanged(positionStart: Int, itemCount: Int, payload: Any?) {
populateTabsFromPagerAdapter()
}
override fun onItemRangeInserted(positionStart: Int, itemCount: Int) {
populateTabsFromPagerAdapter()
}
override fun onItemRangeRemoved(positionStart: Int, itemCount: Int) {
populateTabsFromPagerAdapter()
}
override fun onItemRangeMoved(fromPosition: Int, toPosition: Int, itemCount: Int) {
populateTabsFromPagerAdapter()
}
}
}
ldjcmu
Description: TabLayoutMediator crashes if ViewPager2 adapter item count decreases when last tab was selected.
Expected behavior: Tabs are updated reflecting adapter state (new last tab is selected).
Stack trace:
Source code: See sample project
Android API version: 25, 28
Material Library version: 1.1.0-alpha10 ViewPager2 1.0.0-beta04
Device: Wileyfox Swift, Android Emulator