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[TabLayoutMediator] Support responding to adapter changes #4548

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[TabLayoutMediator] Support responding to adapter changes #4548

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26 changes: 24 additions & 2 deletions lib/java/com/google/android/material/tabs/TabLayoutMediator.java
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,7 @@
import static androidx.viewpager2.widget.ViewPager2.SCROLL_STATE_IDLE;
import static androidx.viewpager2.widget.ViewPager2.SCROLL_STATE_SETTLING;

import android.view.ViewTreeObserver;
import androidx.recyclerview.widget.RecyclerView;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
Expand All @@ -39,8 +40,7 @@
* the mediator object, {@link #attach()} will link the TabLayout and the ViewPager2 together. When
* creating an instance of this class, you must supply an implementation of {@link
* TabConfigurationStrategy} in which you set the text of the tab, and/or perform any styling of the
* tabs that you require. Changing ViewPager2's adapter will require a {@link #detach()} followed by
* {@link #attach()} call. Changing the ViewPager2 or TabLayout will require a new instantiation of
* tabs that you require. Changing the ViewPager2 or TabLayout will require a new instantiation of
* TabLayoutMediator.
*/
public final class TabLayoutMediator {
Expand All @@ -54,6 +54,7 @@ public final class TabLayoutMediator {

@Nullable private TabLayoutOnPageChangeCallback onPageChangeCallback;
@Nullable private TabLayout.OnTabSelectedListener onTabSelectedListener;
@Nullable private ViewPagerOnLayoutListener onLayoutListener;
@Nullable private RecyclerView.AdapterDataObserver pagerAdapterObserver;

/**
Expand Down Expand Up @@ -127,6 +128,13 @@ public void attach() {
onTabSelectedListener = new ViewPagerOnTabSelectedListener(viewPager, smoothScroll);
tabLayout.addOnTabSelectedListener(onTabSelectedListener);

// Here we'll add a listener that responds to adapter changes. Unlike ViewPager,
// ViewPager2 doesn't have a built-in OnAdapterChangeListener, so we'll use a
// slightly different approach that relies on the fact that changing the adapter
// always causes a layout pass (see b/135299048).
onLayoutListener = new ViewPagerOnLayoutListener();
viewPager.getViewTreeObserver().addOnGlobalLayoutListener(onLayoutListener);

// Now we'll populate ourselves from the pager adapter, adding an observer if
// autoRefresh is enabled
if (autoRefresh) {
Expand All @@ -151,8 +159,10 @@ public void detach() {
adapter.unregisterAdapterDataObserver(pagerAdapterObserver);
pagerAdapterObserver = null;
}
viewPager.getViewTreeObserver().removeOnGlobalLayoutListener(onLayoutListener);
tabLayout.removeOnTabSelectedListener(onTabSelectedListener);
viewPager.unregisterOnPageChangeCallback(onPageChangeCallback);
onLayoutListener = null;
onTabSelectedListener = null;
onPageChangeCallback = null;
adapter = null;
Expand Down Expand Up @@ -317,4 +327,16 @@ public void onItemRangeMoved(int fromPosition, int toPosition, int itemCount) {
populateTabsFromPagerAdapter();
}
}

private class ViewPagerOnLayoutListener implements ViewTreeObserver.OnGlobalLayoutListener {

@Override
public void onGlobalLayout() {
RecyclerView.Adapter<?> currentAdapter = viewPager.getAdapter();
if (adapter != currentAdapter) {
detach();
attach();
}
}
}
}