android - 在 PopBackStack 上保留数据

Question

我有一个使用两个 fragment 的 Activity ，MainFragment 和 DetailFragment。 MainFragment 有一个可扩展的 ListView ，其中公司名称作为组，位置名称作为子项。当用户从抽屉导航中选择一个类别时，它会更新适配器中的数据并更新可扩展列表，以显示正确的公司。

当用户选择一个位置时，它会打开包含有关该位置和员工信息的 DetailFragment。我遇到的问题是当我退后一步时。当我点击后退按钮时，它会重置为默认类别，我发现这是因为它再次调用了 onViewCreated() 方法，这是我设置 View 和适配器的地方。奇怪的是，它会记住哪些列表项是按索引展开的。因此，如果我在不同的类别中展开第三项，则默认类别中的第三项仍会展开。

我想知道的是，我怎样才能让它保持我按下后退时的设置？

我的主要 fragment

public class MainFragment extends Fragment implements ExpandableListView.OnChildClickListener, NavigationSelectedListener {

    private CompaniesExpandableListAdapter adapter;

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

    @Override
    public void onCreate(@Nullable 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_main, container, false);
    }

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

        connectViews(view);
    }

    private void connectViews(View view) {
        final ExpandableListView companyListView = (ExpandableListView) view.findViewById(R.id.companyListView);

        final Navigation navigationItem = ((MainActivity) getActivity()).getNavigationItems().first();
        getActivity().setTitle(navigationItem.getTitle());

        adapter = new CompaniesExpandableListAdapter(navigationItem.getCompanies());
        companyListView.setAdapter(adapter);
        companyListView.setOnChildClickListener(this);
    }

    // ExpandableListView.OnChildClickListener
    @Override
    public boolean onChildClick(ExpandableListView parent, View v, int groupPosition, int childPosition, long id) {
        final DetailFragment detailFragment = new DetailFragment();

        final Bundle args = new Bundle();
        args.putInt(getString(R.string.extra_location_key), ((Locations) adapter.getChild(groupPosition, childPosition)).getPrimaryKey());

        detailFragment.setArguments(args);

        getFragmentManager()
                .beginTransaction()
                .replace(R.id.contentFrame, detailFragment, getString(R.string.tag_fragment_detail))
                .addToBackStack(null)
                .commit();

        return false;
    }

    // NavigationSelectedListener
    @Override
    public void onNavigationItemSelected(Navigation navigationItem) {
        // Go back to the main fragment.
        getFragmentManager().popBackStack(getString(R.string.tag_fragment_main), FragmentManager.POP_BACK_STACK_INCLUSIVE);

        // Send the selected item to the adapter.
        adapter.updateData(navigationItem.getCompanies());
        getActivity().setTitle(navigationItem.getTitle());
    }
}

还有我的 MainActivity

public class MainActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener {

    private NavigationSelectedListener navigationCallback;

    private DrawerLayout drawerLayout;

    private RealmResults<Navigation> navigationItems;

    private MainFragment mainFragment = new MainFragment();

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

        buildNavigationDrawer();
        connectViews();
    }

    @Override
    public void onBackPressed() {
        if (drawerLayout.isDrawerOpen(GravityCompat.START)) drawerLayout.closeDrawer(GravityCompat.START);
        else super.onBackPressed();
    }

    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        navigationCallback.onNavigationItemSelected(navigationItems.get(item.getItemId()));

        drawerLayout.closeDrawer(GravityCompat.START);

        return true;
    }

    private void connectViews() {
        navigationCallback = mainFragment;

        getFragmentManager()
                .beginTransaction()
                .replace(R.id.contentFrame, mainFragment, getString(R.string.tag_fragment_main))
                .commit();
    }

    private void buildNavigationDrawer() {
        final Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        drawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);

        final ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(this, drawerLayout, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close) {

            @Override
            public void onDrawerStateChanged(int newState) {
                super.onDrawerStateChanged(newState);

                // Hides the device keyboard when the navigation drawer is opened.
                if (getCurrentFocus() != null) ((InputMethodManager) getSystemService(INPUT_METHOD_SERVICE)).hideSoftInputFromWindow(getCurrentFocus().getWindowToken(), 0);
            }
        };

        drawerLayout.addDrawerListener(toggle);
        toggle.syncState();

        fillNavigationDrawer();
    }

    public RealmResults<Navigation> getNavigationItems() {
        return navigationItems;
    }
}

Answer 1

您应该在交易中使用add 而不是replace。