效果图：

 MainActivity

public class MainActivity extends AppCompatActivity {private TabLayout tabLayout;private ViewPager2 viewPager2;private int activeColor = Color.parseColor("#ff678f");private int normalColor = Color.parseColor("#666666");private int activeSize = 20;private int normalSize = 14;private ArrayList fragments;private TabLayoutMediator mediator;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);tabLayout = findViewById(R.id.tab_layout);viewPager2 = findViewById(R.id.view_pager);final String[] tabs = new String[]{"关注", "推荐", "最新0", "最新1", "最新2", "最新3", "最新4", "最新5", "最新6"};//禁用预加载viewPager2.setOffscreenPageLimit(ViewPager2.OFFSCREEN_PAGE_LIMIT_DEFAULT);//AdapterviewPager2.setAdapter(new FragmentStateAdapter(getSupportFragmentManager(), getLifecycle()) {@NonNull@Overridepublic Fragment createFragment(int position) {//FragmentStateAdapter内部自己会管理已实例化的fragment对象。// 所以不需要考虑复用的问题return TestFragment.newInstance(tabs[position]);}@Overridepublic int getItemCount() {return tabs.length;}});//viewPager 页面切换监听监听viewPager2.registerOnPageChangeCallback(changeCallback);mediator = new TabLayoutMediator(tabLayout, viewPager2, new TabLayoutMediator.TabConfigurationStrategy() {@Overridepublic void onConfigureTab(@NonNull TabLayout.Tab tab, int position) {//这里可以自定义TabViewTextView tabView = new TextView(MainActivity.this);int[][] states = new int[2][];states[0] = new int[]{android.R.attr.state_selected};states[1] = new int[]{};int[] colors = new int[]{activeColor, normalColor};ColorStateList colorStateList = new ColorStateList(states, colors);tabView.setText(tabs[position]);tabView.setTextSize(normalSize);tabView.setTextColor(colorStateList);tab.setCustomView(tabView);}});//要执行这一句才是真正将两者绑定起来mediator.attach();}private ViewPager2.OnPageChangeCallback changeCallback = new ViewPager2.OnPageChangeCallback() {@Overridepublic void onPageSelected(int position) {//可以来设置选中时tab的大小int tabCount = tabLayout.getTabCount();for (int i = 0; i < tabCount; i++) {TabLayout.Tab tab = tabLayout.getTabAt(i);TextView tabView = (TextView) tab.getCustomView();if (tab.getPosition() == position) {tabView.setTextSize(activeSize);tabView.setTypeface(Typeface.DEFAULT_BOLD);} else {tabView.setTextSize(normalSize);tabView.setTypeface(Typeface.DEFAULT);}}}};@Overrideprotected void onDestroy() {mediator.detach();viewPager2.unregisterOnPageChangeCallback(changeCallback);super.onDestroy();}
}

activity_main关键代码

•         tabIndicatorColor  指示器颜色
•         tabIndicatorHeight 指示器高度
•         tabIndicatorFullWidth  设置为false 则指示器跟文本宽度一致
•         tabUnboundedRipple 设置为true点击时会有一个水波纹效果
•         tabGravity 可设置center或fill；center指的是居中显示，fill指的是沾满全屏。
•         tabMode 可设置fixed和 scrollable；fixed：指的是固定tab；scrollable指的是tab可滑动。
•         tabTextColor tab文字颜色
•         tabSelectedTextColor 选中时的tab颜色

viewPager2可以通过设置android:orientation属性来设置切换方向，支持上下、左右切换。

TestFragment

 对应tab页面的实现效果在Fragment中进行实现。

public class TestFragment extends Fragment {private View rootView;public static TestFragment newInstance(String text) {Bundle args = new Bundle();args.putString("text", text);TestFragment fragment = new TestFragment();fragment.setArguments(args);return fragment;}@Nullable@Overridepublic View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {rootView = inflater.inflate(R.layout.fragment_test, container, false);return rootView;}@Overridepublic void onActivityCreated(@Nullable Bundle savedInstanceState) {super.onActivityCreated(savedInstanceState);TextView textView = rootView.findViewById(R.id.text_view);String text = getArguments() != null ? getArguments().getString("text") : null;textView.setText(text);}
}

几个注意的点！！

• ViewPager2获取当前fragment，通过mFragmentManager.findFragmentByTag(XXX); tag前面需要拼接“f”

看下源码tag怎么设置的，调用链如下：

FragmentStateAdapter-》onBindViewHolder-》placeFragmentInViewHolder方法

mFragmentManager.beginTransaction().add(fragment, "f" + holder.getItemId()).setMaxLifecycle(fragment, STARTED).commitNow();

• ViewPager.setOffscreenPageLimit()设置预加载与缓存

（1）ViewPager 会预加载几页
（2）ViewPager 会缓存 2*n+1 页(n为设置的值)

如设置为n=1，预加载页数1页，缓存页数3页。如果当前在第一页，会预加载第二页，滑倒第二页，会预加载第三页，当滑倒第三页，第一页会销毁，第四页会加载。