1. 组成架构

• 整个架构被包在一个外部Fragment之中，也可以放在一个Activity之中，随意。
• 外部的fragment包含了两个组件，即途中的ViewPager和TabLayout
• ViewPager要套上一个FragmentStatePagerAdapter ，适配器负责new出一个个fragment，这些fragment object就是负责装数据的一个个页面。
• ViewPager可以和TabLayout进行关联

2. 实现步骤

2.1 创建内部的fragment object和外部的Fragment

public class ObjectFragment extends Fragment {

    private static String OBJ_INDEX = "objectIndex";
    private String mIndex;
    public ObjectFragment() {
    }

    public static ObjectFragment newInstance(String param1) {
        ObjectFragment fragment = new ObjectFragment();
        Bundle args = new Bundle();
        args.putString(OBJ_INDEX, param1);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            mIndex = getArguments().getString(OBJ_INDEX);
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        return inflater.inflate(R.layout.fragment_object, container, false);
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        ((TextView) view.findViewById(R.id.tv_frg_obj)).setText("item" + mIndex);

    }

}

public class OuterFragment extends Fragment {


    public OuterFragment() {
        // Required empty public constructor
    }

    public static OuterFragment newInstance() {
        OuterFragment fragment = new OuterFragment();
        return fragment;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_outer, container, false);
    }
}

下面是OuterFragment的页面，由架构图可以看出，外部的fragment包含了ViewPager和TabLayout，但是在具体的页面中，TabLayout被放进了ViewPager中

    <androidx.viewpager.widget.ViewPager
        android:id="@+id/pager"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <com.google.android.material.tabs.TabLayout
            android:id="@+id/tab_layout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />

    </androidx.viewpager.widget.ViewPager>

2.2 创建FragmentStatePagerAdapter适配器

这个东西就是ViewPager的适配器

public class MyFragmentStatePagerAdapter extends FragmentStatePagerAdapter {
    public MyFragmentStatePagerAdapter(@NonNull FragmentManager fm) {
        super(fm);
    }

    @NonNull
    @Override
    public Fragment getItem(int position) {
        Fragment fragment = ObjectFragment.newInstance(position + 1 + "");
        return fragment;
    }

    @Override
    public int getCount() {
        return 10;
    }
    
    @Override
    public CharSequence getPageTitle(int position) {
        return "" + (position + 1);
    }

}

2.3 给ViewPager设置适配器

这里的步骤都在OuterFragment中操作

添加以下成员：

MyFragmentStatePagerAdapter fragmentStatePagerAdapter;
ViewPager viewPager;

在以下函数中进行设置：

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        //设置ViewPager的适配器
        viewPager = view.findViewById(R.id.pager);
        fragmentStatePagerAdapter = new MyFragmentStatePagerAdapter(getChildFragmentManager());
        viewPager.setAdapter(fragmentStatePagerAdapter);
        //设置TabLayout与viewPager关联
        TabLayout tabLayout = view.findViewById(R.id.tab_layout);
        tabLayout.setupWithViewPager(viewPager);

    }

3. 启动

在MainActivity中添加外部的OuterFragment

3.1 布局文件中添加FrameLayout

<FrameLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/fr_container"
        android:orientation="horizontal">
</FrameLayout>

3.2 启动Fragment

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        OuterFragment outerFragment = new OuterFragment();
        FragmentManager manager = getSupportFragmentManager();
        FragmentTransaction transaction = manager.beginTransaction();
        transaction.add(R.id.fr_container, outerFragment,"1");
        transaction.addToBackStack(null);
        transaction.commit();

    }
}