不要在BottomNavigationView中重新创建片段

Question

问题：

每次单击BottomNavigationView时，都会重新创建片段。

目前在每个片段中，我都有Recycler View，在创建片段时只运行一次。

在这种情况下，每次都会加载RecyclerView数据。这不是我想要的。

我怎么能工作，以便片段在第一次点击后保持活动状态。当你回到已经创建的Fragment时，只需显示它而不是每次都重新创建它？

我的尝试：

BottomNavigationView bottomNavigationView =(BottomNavigationView) findViewById(R.id.bottomNavView_Bar);
BottomNavigationViewHelper.disableShiftMode(bottomNavigationView);

final Menu menu = bottomNavigationView.getMenu();
fragmentManager = getSupportFragmentManager();
final FragmentTransaction transaction = fragmentManager.beginTransaction();

/* Fragmento Start */
transaction.replace(R.id.content_home, new MainFragment()).commit();


bottomNavigationView.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        Intent in;
        Fragment fragment = null;
        Fragment currentFragment = getSupportFragmentManager().findFragmentById(R.id.content_home);
        switch (item.getItemId()){

            case R.id.ic_home:

                if (!(currentFragment instanceof MainFragment)) {
                    fragment = new MainFragment();
                    toolbar.setTitle("Main");
                    item = menu.getItem(0);
                    item.setChecked(true);
                }

                break;

            case R.id.ic_categorias:

                if (!(currentFragment instanceof CategoriasFragment)) {
                    fragment = new CategoriasFragment();
                    toolbar.setTitle("Categorias");
                    item = menu.getItem(1);
                    item.setChecked(true);
                }
                break;



            case R.id.ic_calendar:

                if (!(currentFragment instanceof FeedUserFragment)) {
                    fragment = new FeedUserFragment();
                    item = menu.getItem(2);
                    toolbar.setTitle("Feed");
                    item.setChecked(true);
                }
                break;

            case R.id.ic_explore:

                if (!(currentFragment instanceof ExploreFragment)) {
                    fragment = new ExploreFragment();
                    item = menu.getItem(3);
                    toolbar.setTitle("Explorar");
                    item.setChecked(true);
                }
                break;

            case R.id.ic_person:

                if (!(currentFragment instanceof Opcoes)) {
                    fragment = new Opcoes();
                    toolbar.setTitle("Opções");
                    item = menu.getItem(4);
                    item.setChecked(true);
                }
                break;

        }

        FragmentManager manager = getSupportFragmentManager();
        FragmentTransaction transaction = manager.beginTransaction();
        transaction.replace(R.id.content_home, fragment);
        transaction.commit();

        return false;

    }
});

Answer 1

您每次都在替换片段，即在切换块完成后。

解决方案：仅在条件满足时更换并使用有助于维护堆栈的addToBackStack。您可以从this网站了解更多信息

试试这个，

bottomNavigationView.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        Intent in;
        Fragment fragment = null;
        Fragment currentFragment = getSupportFragmentManager().findFragmentById(R.id.content_home);
        switch (item.getItemId()){

            case R.id.ic_home:

                if (!(currentFragment instanceof MainFragment)) {
                    fragment = new MainFragment();
                    toolbar.setTitle("Main");
                    item = menu.getItem(0);
                    item.setChecked(true);
                    loadFragment(fragment,"mainMenu");
                }

                break;

            case R.id.ic_categorias:

                if (!(currentFragment instanceof CategoriasFragment)) {
                    fragment = new CategoriasFragment();
                    toolbar.setTitle("Categorias");
                    item = menu.getItem(1);
                    item.setChecked(true);
                    loadFragment(fragment,"categories");
                }
                break;



            case R.id.ic_calendar:

                if (!(currentFragment instanceof FeedUserFragment)) {
                    fragment = new FeedUserFragment();
                    item = menu.getItem(2);
                    toolbar.setTitle("Feed");
                    item.setChecked(true);
                    loadFragment(fragment,"feedUsers");
                }
                break;

            case R.id.ic_explore:

                if (!(currentFragment instanceof ExploreFragment)) {
                    fragment = new ExploreFragment();
                    item = menu.getItem(3);
                    toolbar.setTitle("Explorar");
                    item.setChecked(true);
                    loadFragment(fragment,"explore");
                }
                break;

            case R.id.ic_person:

                if (!(currentFragment instanceof Opcoes)) {
                    fragment = new Opcoes();
                    toolbar.setTitle("Opções");
                    item = menu.getItem(4);
                    item.setChecked(true);
                    loadFragment(fragment,"opcoes");
                }
                break;

        }



        return false;

    }
});

/**
 * Create new method which replace your old fragment
 */
public void loadFragment(Fragment fragment, String tag){
            FragmentManager manager = getSupportFragmentManager();
            FragmentTransaction transaction = manager.beginTransaction();
            transaction.replace(R.id.content_home, fragment);
            transaction.addToBackStack(tag);
            transaction.commit();

}

Answer 2

我会尝试transaction.add()并使用此方法findFragmentByTag搜索后堆栈中的片段。 https://developer.android.com/reference/android/support/v4/app/FragmentManager.html#findFragmentByTag(java.lang.String)。