在viewpager中保存和恢复片段状态

@Override
public void onSaveInstanceState(@NonNull Bundle outState) {
    super.onSaveInstanceState(outState);
    // 手动保存需要的状态
    outState.putString("key", "value");
}

@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (savedInstanceState != null) {
        String value = savedInstanceState.getString("key");
        // 恢复状态
    }
}

public class MyFragment extends Fragment {
    private String savedValue;

    @Override
    public void onSaveInstanceState(@NonNull Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putString("key", savedValue);
    }

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (savedInstanceState != null) {
            savedValue = savedInstanceState.getString("key");
        }
    }
}

public class MyPagerAdapter extends FragmentStatePagerAdapter {
    public MyPagerAdapter(@NonNull FragmentManager fm, int behavior) {
        super(fm, behavior);
    }

    @NonNull
    @Override
    public Fragment getItem(int position) {
        return new MyFragment();
    }

    @Override
    public int getCount() {
        return NUM_PAGES;
    }
}

public class MainActivity extends AppCompatActivity {
    private ViewPager viewPager;
    private MyPagerAdapter pagerAdapter;

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

        viewPager = findViewById(R.id.viewPager);
        pagerAdapter = new MyPagerAdapter(getSupportFragmentManager(), FragmentStatePagerAdapter.BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT);
        viewPager.setAdapter(pagerAdapter);
    }
}