在BottomNavigationView中不重新创建片段

Question

Problem:

Each time the BottomNavigationView is clicked the fragment is re-created.

Currently in each fragment I have Recycler View that runs only once when creating the Fragment.

In this case, the RecyclerView data is loaded every time. And that's not what I'd like.

How could I work so that the Fragment remains active after it is clicked the first time. And when you go back to the Fragment already created, just display it without recreating it every time?

My attempts:

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

You are replacing your fragment every time ie after your switch block complete.

Solution : Replace only when condition meets and use addToBackStack which helps to maintain stacks. You can read more about from this site

Try this,

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

I would try transaction.add() and search for fragments in back stack with this method findFragmentByTag . https://developer.android.com/reference/android/support/v4/app/FragmentManager.html#findFragmentByTag(java.lang.String) .