How to maintain backstack of fragment in Navigation Drawer?

Question

I have taken one activity and with activity I have attached navigation drawer and the home fragment. In that navigation drawer there is a option of "Contact Us". When user click on that option a fragment gets open. But I am not able to maintain the stack of that. means when I am on contact us fragment then using navigation drawer again click on contact us it overlaps previous one. I have to press back button 2 times to go on home fragment. Please Help me how to maintain back stack for this. Here is my code..

navigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem item) {
                int id = item.getItemId();
                switch (id) {

                    case R.id.rate:

                        Uri uri = Uri.parse("market://details?id=" + getPackageName());
                        Intent myAppLinkToMarket = new Intent(Intent.ACTION_VIEW, uri);
                        try {
                            startActivity(myAppLinkToMarket);
                        } catch (ActivityNotFoundException e) {
                            Toast.makeText(getApplicationContext(), "Unable to find source market app!", Toast.LENGTH_SHORT).show();
                        }
                        break;


                    case R.id.contact_us:

                        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
                        transaction.add(R.id.fragment_container_dashboard, ContactUsFragment.newInstance());
                        transaction.addToBackStack(null);
                        transaction.commit();
                        mDrawerLayout.closeDrawer(GravityCompat.START);


                        break;

                }
                return false;
            }
        });

After this code I use this to maintain back stack:

@Override
    public void onBackPressed() {
        if (getFragmentManager().getBackStackEntryCount() != 0) {
            getFragmentManager().popBackStack();
        }

        else new AlertDialog.Builder(this)
                .setMessage("Are you sure you want to exit?")
                .setCancelable(false)
                .setPositiveButton("Yes", new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int id) {
                        Dashboard.super.onBackPressed();
                    }
                })
                .setNegativeButton("No", null)
                .show();
    }

But the issue is It's show exit dialogue on contact us fragment when ever I press back button. But I want firstly I reach to home fragment and after that If I press back button then it show exit dialogue.

Answer 1

I solved this by adding this in the onCreate method.

getSupportFragmentManager().addOnBackStackChangedListener(new FragmentManager.OnBackStackChangedListener() {
        @Override
        public void onBackStackChanged() {
            if(getSupportFragmentManager().getBackStackEntryCount() == 0){
                drawer.setDrawerLockMode(DrawerLayout.LOCK_MODE_UNLOCKED);
                menuToggle.setDrawerIndicatorEnabled(true);
                // your dialog
            }else{
                drawer.setDrawerLockMode(DrawerLayout.LOCK_MODE_LOCKED_CLOSED);
                menuToggle.setDrawerIndicatorEnabled(false);
                // remove to your previous fragment
            }
        }
    });