Separate Back Stack for each tab in BottomNavigationView Android using Fragments

Question

I\'m implementing BottomNavigationView for navigation in an Android app. I am using Fragments to set the content for each tab.

I know how to set up one

Answer 1

Finally, I found the solution, it was inspired by a previous answer on StackOverflow: Separate Back Stack for each tab in Android using Fragments
I only have replaced TabHost with BottomNavigationView and here is the code:
Main Activity

public class MainActivity extends AppCompatActivity {

private HashMap> mStacks;
public static final String TAB_HOME  = "tab_home";
public static final String TAB_DASHBOARD  = "tab_dashboard";
public static final String TAB_NOTIFICATIONS  = "tab_notifications";

private String mCurrentTab;

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

    BottomNavigationView navigation = (BottomNavigationView) findViewById(R.id.navigation);
    navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);

    mStacks = new HashMap>();
    mStacks.put(TAB_HOME, new Stack());
    mStacks.put(TAB_DASHBOARD, new Stack());
    mStacks.put(TAB_NOTIFICATIONS, new Stack());

    navigation.setSelectedItemId(R.id.navigation_home);
}

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

    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        switch (item.getItemId()) {
            case R.id.navigation_home:
                selectedTab(TAB_HOME);
                return true;
            case R.id.navigation_dashboard:
                selectedTab(TAB_DASHBOARD);
                return true;
            case R.id.navigation_notifications:
                selectedTab(TAB_NOTIFICATIONS);
                return true;
        }
        return false;
    }

};

private void gotoFragment(Fragment selectedFragment)
{
    FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
    fragmentTransaction.replace(R.id.content, selectedFragment);
    fragmentTransaction.commit();
}

private void selectedTab(String tabId)
{
    mCurrentTab = tabId;

    if(mStacks.get(tabId).size() == 0){
      /*
       *    First time this tab is selected. So add first fragment of that tab.
       *    Dont need animation, so that argument is false.
       *    We are adding a new fragment which is not present in stack. So add to stack is true.
       */
        if(tabId.equals(TAB_HOME)){
            pushFragments(tabId, new HomeFragment(),true);
        }else if(tabId.equals(TAB_DASHBOARD)){
            pushFragments(tabId, new DashboardFragment(),true);
        }else if(tabId.equals(TAB_NOTIFICATIONS)){
            pushFragments(tabId, new NotificationsFragment(),true);
        }
    }else {
      /*
       *    We are switching tabs, and target tab is already has atleast one fragment.
       *    No need of animation, no need of stack pushing. Just show the target fragment
       */
        pushFragments(tabId, mStacks.get(tabId).lastElement(),false);
    }
}

public void pushFragments(String tag, Fragment fragment, boolean shouldAdd){
    if(shouldAdd)
        mStacks.get(tag).push(fragment);
    FragmentManager manager = getSupportFragmentManager();
    FragmentTransaction ft = manager.beginTransaction();
    ft.replace(R.id.content, fragment);
    ft.commit();
}

public void popFragments(){
  /*
   *    Select the second last fragment in current tab's stack..
   *    which will be shown after the fragment transaction given below
   */
    Fragment fragment = mStacks.get(mCurrentTab).elementAt(mStacks.get(mCurrentTab).size() - 2);

  /*pop current fragment from stack.. */
    mStacks.get(mCurrentTab).pop();

  /* We have the target fragment in hand.. Just show it.. Show a standard navigation animation*/
    FragmentManager manager = getSupportFragmentManager();
    FragmentTransaction ft = manager.beginTransaction();
    ft.replace(R.id.content, fragment);
    ft.commit();
}

@Override
public void onBackPressed() {
    if(mStacks.get(mCurrentTab).size() == 1){
        // We are already showing first fragment of current tab, so when back pressed, we will finish this activity..
        finish();
        return;
    }

    /* Goto previous fragment in navigation stack of this tab */
    popFragments();
}

}

Home fragment example

public class HomeFragment extends Fragment {
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_home, container, false);
    Button gotoNextFragment = (Button) view.findViewById(R.id.gotoHome2);

    gotoNextFragment.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            ((MainActivity)getActivity()).pushFragments(MainActivity.TAB_HOME, new Home2Fragment(),true);
        }
    });
    return view;
}

}