Android 有个ViewPager，但是在Androidx 的jetpack 中出现了ViewPager2，官方也建议使用这个类替代ViewPager，但是之前的TabLayout 都是绑定的ViewPager :
public void setupWithViewPager(@Nullable ViewPager viewPager) {
this.setupWithViewPager(viewPager, true);
}
public void setupWithViewPager(@Nullable ViewPager viewPager, boolean autoRefresh) {
this.setupWithViewPager(viewPager, autoRefresh, false);
}
那么怎么使用ViewPager2 和TabLayout呢？
方案一：
网上已经给出了一个教程，就是 Copy 一个类叫TabLayoutMediator的类,然后放在固定包名下面：com.google.android.material.tabs:
TabLayoutMediator.png
方案二：
更新material 库 到com.google.android.material:material:1.1.0-alpha09@aar及以上，你就会看到Google 爸爸已经自己更新到上面了，好东西不会留着自己用了。
TabLayoutMediator
用法
public class TestConfigActivity extends BaseActivity {
private List<Fragment> mFragments;
private final static String[] NAMES = {"a", "b", "c", "d"};
private TabLayoutMediator mLayoutMediator;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.test_main);
TabLayout tabLayout = findViewById(R.id.tab_layout);
initData();
ViewPager2 viewPager2 = findViewById(R.id.test_view_page);
viewPager2.setAdapter(new FragmentStateAdapter(this) {
@NonNull
@Override
public Fragment createFragment(int position) {
return mFragments.get(position);
}
@Override
public int getItemCount() {
return mFragments.size();
}
});
mLayoutMediator = new TabLayoutMediator(tabLayout, viewPager2, false, true,
(tab, position) -> tab.setText(NAMES[position]));
mLayoutMediator.attach();
}
private void initData() {
mFragments = new ArrayList<>();
mFragments.add(new TestConfigFragment());
mFragments.add(new TestSwitchFragment());
mFragments.add(new TestUIFragment());
mFragments.add(new TestOtherFragment());
}
@Override
protected void onDestroy() {
super.onDestroy();
mLayoutMediator.detach();
}
}
这个是源码，为啥我会贴源码呢，因为之前这个类是在 Google内部的库的frameWork层，只有内部的一些框架能用到，不想更新 material库的可以直接cp源码，定义好包名的方式去搞。
TabLayoutMediator 源码
/*
* Copyright 2018 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 com.google.android.material.tabs;
import static androidx.viewpager2.widget.ViewPager2.SCROLL_STATE_DRAGGING;
import static androidx.viewpager2.widget.ViewPager2.SCROLL_STATE_IDLE;
import static androidx.viewpager2.widget.ViewPager2.SCROLL_STATE_SETTLING;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.recyclerview.widget.RecyclerView;
import androidx.viewpager2.widget.ViewPager2;
import java.lang.ref.WeakReference;
/**
* A mediator to link a TabLayout with a ViewPager2. The mediator will synchronize the ViewPager2's
* position with the selected tab when a tab is selected, and the TabLayout's scroll position when
* the user drags the ViewPager2.
*
* <p>Establish the link by creating an instance of this class, make sure the ViewPager2 has an
* adapter and then call {@link #attach()} on it. When creating an instance of this class, you must
* supply an implementation of {@link OnConfigureTabCallback} in which you set the text of the tab,
* and/or perform any styling of the tabs that you require.
*/
public final class TabLayoutMediator {
@NonNull private final TabLayout tabLayout;
@NonNull private final ViewPager2 viewPager;
private final boolean autoRefresh;
private final OnConfigureTabCallback onConfigureTabCallback;
private RecyclerView.Adapter<?> adapter;
private boolean attached;
private TabLayoutOnPageChangeCallback onPageChangeCallback;
private TabLayout.OnTabSelectedListener onTabSelectedListener;
private RecyclerView.AdapterDataObserver pagerAdapterObserver;
/**
* A callback interface that must be implemented to set the text and styling of newly created
* tabs.
*/
public interface OnConfigureTabCallback {
/**
* Called to configure the tab for the page at the specified position. Typically calls {@link
* TabLayout.Tab#setText(CharSequence)}, 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.
*/
void onConfigureTab(@NonNull TabLayout.Tab tab, int position);
}
public TabLayoutMediator(
@NonNull TabLayout tabLayout,
@NonNull ViewPager2 viewPager,
@NonNull OnConfigureTabCallback onConfigureTabCallback) {
this(tabLayout, viewPager, true, onConfigureTabCallback);
}
public TabLayoutMediator(
@NonNull TabLayout tabLayout,
@NonNull ViewPager2 viewPager,
boolean autoRefresh,
@NonNull OnConfigureTabCallback onConfigureTabCallback) {
this.tabLayout = tabLayout;
this.viewPager = viewPager;
this.autoRefresh = autoRefresh;
this.onConfigureTabCallback = onConfigureTabCallback;
}
/**
* Link the TabLayout and the ViewPager2 together.
*
* @throws IllegalStateException If the mediator is already attached, or the ViewPager2 has no
* adapter.
*/
public void attach() {
if (attached) {
throw new IllegalStateException("TabLayoutMediator is already attached");
}
adapter = viewPager.getAdapter();
if (adapter == null) {
throw new IllegalStateException(
"TabLayoutMediator attached before ViewPager2 has an " + "adapter");
}
attached = true;
// Add our custom OnPageChangeCallback to the ViewPager
onPageChangeCallback = new TabLayoutOnPageChangeCallback(tabLayout);
viewPager.registerOnPageChangeCallback(onPageChangeCallback);
// Now we'll add a tab selected listener to set ViewPager's current item
onTabSelectedListener = new ViewPagerOnTabSelectedListener(viewPager);
tabLayout.addOnTabSelectedListener(onTabSelectedListener);
// 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 = new PagerAdapterObserver();
adapter.registerAdapterDataObserver(pagerAdapterObserver);
}
populateTabsFromPagerAdapter();
// Now update the scroll position to match the ViewPager's current item
tabLayout.setScrollPosition(viewPager.getCurrentItem(), 0f, true);
}
/** Unlink the TabLayout and the ViewPager */
public void detach() {
adapter.unregisterAdapterDataObserver(pagerAdapterObserver);
tabLayout.removeOnTabSelectedListener(onTabSelectedListener);
viewPager.unregisterOnPageChangeCallback(onPageChangeCallback);
pagerAdapterObserver = null;
onTabSelectedListener = null;
onPageChangeCallback = null;
attached = false;
}
@SuppressWarnings("WeakerAccess")
void populateTabsFromPagerAdapter() {
tabLayout.removeAllTabs();
if (adapter != null) {
int adapterCount = adapter.getItemCount();
for (int i = 0; i < adapterCount; i++) {
TabLayout.Tab tab = tabLayout.newTab();
onConfigureTabCallback.onConfigureTab(tab, i);
tabLayout.addTab(tab, false);
}
// Make sure we reflect the currently set ViewPager item
if (adapterCount > 0) {
int currItem = viewPager.getCurrentItem();
if (currItem != tabLayout.getSelectedTabPosition()) {
tabLayout.getTabAt(currItem).select();
}
}
}
}
/**
* A {@link ViewPager2.OnPageChangeCallback} class which contains the necessary calls back to the
* provided {@link TabLayout} so that the tab position is kept in sync.
*
* <p>This class stores the provided TabLayout weakly, meaning that you can use {@link
* ViewPager2#registerOnPageChangeCallback(ViewPager2.OnPageChangeCallback)} without removing the
* callback and not cause a leak.
*/
private static class TabLayoutOnPageChangeCallback extends ViewPager2.OnPageChangeCallback {
private final WeakReference<TabLayout> tabLayoutRef;
private int previousScrollState;
private int scrollState;
TabLayoutOnPageChangeCallback(TabLayout tabLayout) {
tabLayoutRef = new WeakReference<>(tabLayout);
reset();
}
@Override
public void onPageScrollStateChanged(final int state) {
previousScrollState = scrollState;
scrollState = state;
}
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
TabLayout tabLayout = tabLayoutRef.get();
if (tabLayout != null) {
// Only update the text selection if we're not settling, or we are settling after
// being dragged
boolean 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.
boolean updateIndicator =
!(scrollState == SCROLL_STATE_SETTLING && previousScrollState == SCROLL_STATE_IDLE);
tabLayout.setScrollPosition(position, positionOffset, updateText, updateIndicator);
}
}
@Override
public void onPageSelected(final int position) {
TabLayout tabLayout = tabLayoutRef.get();
if (tabLayout != null
&& tabLayout.getSelectedTabPosition() != position
&& position < tabLayout.getTabCount()) {
// Select the tab, only updating the indicator if we're not being dragged/settled
// (since onPageScrolled will handle that).
boolean updateIndicator =
scrollState == SCROLL_STATE_IDLE
|| (scrollState == SCROLL_STATE_SETTLING
&& previousScrollState == SCROLL_STATE_IDLE);
tabLayout.selectTab(tabLayout.getTabAt(position), updateIndicator);
}
}
void reset() {
previousScrollState = scrollState = SCROLL_STATE_IDLE;
}
}
/**
* A {@link TabLayout.OnTabSelectedListener} class which contains the necessary calls back to the
* provided {@link ViewPager2} so that the tab position is kept in sync.
*/
private static class ViewPagerOnTabSelectedListener implements TabLayout.OnTabSelectedListener {
private final ViewPager2 viewPager;
ViewPagerOnTabSelectedListener(ViewPager2 viewPager) {
this.viewPager = viewPager;
}
@Override
public void onTabSelected(TabLayout.Tab tab) {
viewPager.setCurrentItem(tab.getPosition(), true);
}
@Override
public void onTabUnselected(TabLayout.Tab tab) {
// No-op
}
@Override
public void onTabReselected(TabLayout.Tab tab) {
// No-op
}
}
private class PagerAdapterObserver extends RecyclerView.AdapterDataObserver {
PagerAdapterObserver() {}
@Override
public void onChanged() {
populateTabsFromPagerAdapter();
}
@Override
public void onItemRangeChanged(int positionStart, int itemCount) {
populateTabsFromPagerAdapter();
}
@Override
public void onItemRangeChanged(int positionStart, int itemCount, @Nullable Object payload) {
populateTabsFromPagerAdapter();
}
@Override
public void onItemRangeInserted(int positionStart, int itemCount) {
populateTabsFromPagerAdapter();
}
@Override
public void onItemRangeRemoved(int positionStart, int itemCount) {
populateTabsFromPagerAdapter();
}
@Override
public void onItemRangeMoved(int fromPosition, int toPosition, int itemCount) {
populateTabsFromPagerAdapter();
}
}
}
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