Example of activity using CustosmBottomNavigationBar registering menu items and controlling the back stack

MainActivity.java

// include package path here

import android.support.v4.app.FragmentManager;
import android.widget.Toast;

import br.com.intelize.onhome.presenter.R;
import br.com.intelize.onhome.presenter.components.CustomBottomNavigationView;
import br.com.intelize.onhome.presenter.view.base.BaseActivity;
import br.com.intelize.onhome.presenter.view.fragment.BillsFragment;
import br.com.intelize.onhome.presenter.view.fragment.SettingsFragment;
import br.com.intelize.onhome.presenter.view.fragment.ShoppingFragment;
import br.com.intelize.onhome.presenter.view.fragment.SummaryFragment;
import br.com.intelize.onhome.presenter.view.fragment.TasksFragment;
import butterknife.BindView;

public class MainActivity extends BaseActivity {

    private Boolean ACTIVITY_BACKPRESSED_EXIT = false;

    @BindView(R.id.bottom_bar_view)
    CustomBottomNavigationView bottomBarView;

    @Override
    protected int getActivityLayout() {
        return R.layout.activity_main;
    }

    protected void configureActivity() {
        configureMenuNavigation();
        configureMainFragment();
    }

    @Override
    protected void onResume() {
        super.onResume();
        ACTIVITY_BACKPRESSED_EXIT = false;
    }

    private void configureMenuNavigation() {
        bottomBarView.registerFragmentToBarItem(R.id.item_summary, SummaryFragment.class, () -> showFragment(R.id.fragment_container, SummaryFragment.newInstance()));

        bottomBarView.registerFragmentToBarItem(R.id.item_bills, BillsFragment.class, () -> showFragment(R.id.fragment_container, BillsFragment.newInstance()));

        bottomBarView.registerFragmentToBarItem(R.id.item_tasks, TasksFragment.class, () -> showFragment(R.id.fragment_container, TasksFragment.newInstance()));

        bottomBarView.registerFragmentToBarItem(R.id.item_shopping, ShoppingFragment.class, () -> showFragment(R.id.fragment_container, ShoppingFragment.newInstance()));

        bottomBarView.registerFragmentToBarItem(R.id.item_settings, SettingsFragment.class, () -> showFragment(R.id.fragment_container, SettingsFragment.newInstance()));
    }

    private void configureMainFragment() {
        showFragment(R.id.fragment_container, new SummaryFragment());
    }

    @Override
    public void onBackPressed() {
        FragmentManager fragmentManager = getSupportFragmentManager();
        int backStackCount = fragmentManager.getBackStackEntryCount();

        if (backStackCount > 1) {
            if (fragmentManager.popBackStackImmediate()) {
                bottomBarView.setSelectedByFragmentManager(fragmentManager);
            }
            ACTIVITY_BACKPRESSED_EXIT = false;
        } else {
            if(!ACTIVITY_BACKPRESSED_EXIT){
                Toast.makeText(this, getResources().getString(R.string.activity_toast_backpressed), Toast.LENGTH_LONG).show();
                ACTIVITY_BACKPRESSED_EXIT = true;
            } else {
                moveTaskToBack(true);
            }
        }
    }
}