Android - PageView in new BottomNavigationBar - prevent reload fragments

Question

In my StartActivity the BottomNavigationBar Listener has the following setup:

private GuideFragment guideFragment = new GuideFragment();
private MapFragment mapFragment = new MapFragment();
private MoreFragment moreFragment = new MoreFragment();

private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
        = new BottomNavigationView.OnNavigationItemSelectedListener() {

    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        Fragment selectedFragment = null;
        switch (item.getItemId()) {
            case R.id.navigation_guide:
                selectedFragment = guideFragment;
                break;
            case R.id.navigation_map:
                selectedFragment = mapFragment;
                break;
            case R.id.navigation_more:
                selectedFragment = moreFragment;
                break;
        }
        FragmentTransaction transaction = getFragmentManager().beginTransaction();
        transaction.replace(R.id.content, selectedFragment);
        transaction.commit();
        return true;
    }

};

As I mentioned above I want to prevent that the selected fragments always reloads the sources/view. I tried out some stuff like - in the fragments:

if (rootView == null)
     inflater.inflate...

But the fragments still recreate the view and load (in my case) webresources new.

I read something that a PageView could help, especially

offScreenPageLimit

should do the magic.

My main question is where should I implement a PageViewer - Is it possible in my StartActivity? Or can I solve the problem in an other way?

Are your fragments contents directly or tangentially related? That is, can the contents of each fragment exist and make sense without the others? If not, then perhaps switching a tabbed navigation with a `ViewPager` would better suit your requirements. — CzarMatt, Jun 05 '17 at 19:09
All three fragments are in a different view/tab. Is View Pager then an own class or can I add it in my activity? — Tobias Alt, Jun 05 '17 at 19:11
Or that I understand it correctly - Should I have to remove the BottomNavigation and replace it with a ViewPager? — Tobias Alt, Jun 05 '17 at 19:12
Yes - consider the _type_ of content you are showing and choose the best widget to show that content. Review https://material.io/guidelines/components/bottom-navigation.html and then the ViewPager docs. Probably `ViewPager` would work better for your requirements. — CzarMatt, Jun 05 '17 at 19:14
Okay thanks CzarMatt. But I can not really believe that Android/Google team provides a BottomNavigationBar without handling fragment lifecycles. Sure it is a bit new stuff - but always call a new instance of a tab is... — Tobias Alt, Jun 05 '17 at 19:17

score 4 · Accepted Answer · edited Jun 20 '20 at 17:57

I did it boys! There is no ViewPager necessary.

Here is my solution (all coded in StartActivity not in Fragments):

private final GuideFragment guideFragment = new GuideFragment();
private final MapFragment mapFragment = new MapFragment();
private final MoreFragment moreFragment = new MoreFragment();
private final android.app.FragmentManager fm = getFragmentManager();
Fragment active = guideFragment;

private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
        = new BottomNavigationView.OnNavigationItemSelectedListener() {

    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        switch (item.getItemId()) {
            case R.id.navigation_guide:
                if(active != guideFragment) {
                    fm.beginTransaction().show(guideFragment).commit();
                }
                else {
                    fm.beginTransaction().hide(active).show(guideFragment).commit();
                }
                active = guideFragment;
                break;
            case R.id.navigation_map:
                fm.beginTransaction().hide(active).show(mapFragment).commit();
                active = mapFragment;
                break;
            case R.id.navigation_more:
                fm.beginTransaction().hide(active).show(moreFragment).commit();
                active = moreFragment;
                break;
        }

        return true;
    }

};

and in onCreate list the transaction commits.

fm.beginTransaction().add(R.id.content,moreFragment).commit();
fm.beginTransaction().add(R.id.content, mapFragment).commit();
fm.beginTransaction().add(R.id.content, guideFragment).commit();

It is very important to commit the first tabs fragment last(fragm3,fragm2,fragm1) if you have 3 tabs.

Highly speed performance on the smartphone now by not loading every fragment new/refresh.

Android - PageView in new BottomNavigationBar - prevent reload fragments

1 Answers1

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