Navigation drawer, handling the back button to go to previous fragments?

Question

I\'m using the built-in navigation drawer to run my app. I can\'t quite figure out how to handle the back button. When it\'s pressed I want it to load the very first fragmen

Answer 1

I have 4 fragment attached to bottomnavigation activity and i recently got into this problem and successfulyy solved as follows my activity code

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentTransaction;
import androidx.navigation.NavController;
import androidx.navigation.Navigation;
import androidx.navigation.ui.NavigationUI;

import android.os.Bundle;
import android.view.MenuItem;

import com.google.android.material.bottomnavigation.BottomNavigationView;

public class BottomNavigationActivity extends AppCompatActivity
{
    NavController navController;
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_bottom_navigation);


        BottomNavigationView bottomNavigationView=findViewById(R.id.bottom_navigation);
        bottomNavigationView.setOnNavigationItemSelectedListener(navListener);

        getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,new FragmentHome()).commit();


    }

    public boolean onSupportNavigateUp() {
        return navController.navigateUp();
    }

    private BottomNavigationView.OnNavigationItemSelectedListener navListener= new
            BottomNavigationView.OnNavigationItemSelectedListener()
            {
                @Override
                public boolean onNavigationItemSelected(@NonNull MenuItem item)
                {

                    Fragment selectedFragment = null ;


                    switch (item.getItemId())
                    {

                        case R.id.nav_home:
                            selectedFragment = new FragmentHome();

                            break;

                        case R.id.nav_search:
                            BottomNavigationActivity.this.getSupportFragmentManager().beginTransaction()
                                    .addToBackStack(null)
                                    .commit();
                            selectedFragment=new FragmentSearch();
                            break;

                        case R.id.nav_cart:
                            BottomNavigationActivity.this.getSupportFragmentManager().beginTransaction()
                                    .addToBackStack(null)
                                    .commit();
                            selectedFragment=new FragmentCart();
                            break;

                        case R.id.nav_user:
                            BottomNavigationActivity.this.getSupportFragmentManager().beginTransaction()
                                    .addToBackStack(null)
                                    .commit();
                                selectedFragment= new FragmentAccount();
                                        break;


                    }

                    getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,
                            selectedFragment).commit();

                    return true;

                }
            };


    @Override
    public void onBackPressed()
    {
        int backStackEntryCount = getSupportFragmentManager().getBackStackEntryCount();
        if (backStackEntryCount == 0) {
            super.onBackPressed();
        } else
            {
            goHome();
        }
    }

    public void goHome()
    {
        //Following code will set the icon of the bottom navigation to active
        final BottomNavigationView mBottomNav = findViewById(R.id.bottom_navigation);
        MenuItem homeItem = mBottomNav.getMenu().getItem(0);
        mBottomNav.setSelectedItemId(homeItem.getItemId());
        getSupportFragmentManager().popBackStackImmediate();

        //To delete all entries from back stack immediately one by one.
        int backStackEntry = getSupportFragmentManager().getBackStackEntryCount();
        for (int i = 0; i < backStackEntry; i++) {
            getSupportFragmentManager().popBackStackImmediate();
        }
        //To navigate to the Home Fragment
        final FragmentHome homeFragment = new FragmentHome();
        FragmentTransaction myFragmentTransaction = getSupportFragmentManager().beginTransaction();
        myFragmentTransaction.replace(R.id.fragment_container, homeFragment, "HomeFrag Tag");
        myFragmentTransaction.commit();
    }
}