Android Important Source Code

1. Code to handle onBackPressed in navigation drawer.

    private int stackHeight;
    private void intializeBackStack() {
        getSupportFragmentManager().addOnBackStackChangedListener(new FragmentManager.OnBackStackChangedListener() {
            @Override
            public void onBackStackChanged() {
                stackHeight = getSupportFragmentManager().getBackStackEntryCount();
                Log.e("StackVal", ": " + stackHeight);
                if (stackHeight > 0) {
                    // if we have something on the stack (doesn't include the current shown fragment)
                    getSupportActionBar().setHomeButtonEnabled(true);
                    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
                    toolbar.setNavigationOnClickListener(new View.OnClickListener() {
                        @Override
                        public void onClick(View v) {
                            onBackPressed();
                        }
                    });

                } else {
                    getSupportActionBar().setDisplayHomeAsUpEnabled(false);
                    toggle.syncState();
                    toolbar.setNavigationOnClickListener(new View.OnClickListener() {
                        @Override
                        public void onClick(View v) {
                            drawer.openDrawer(GravityCompat.START);
                        }
                    });
                }
            }

        });
    }


    @Override
    public void onBackPressed() {

        Log.e(TAG, "onBackPressed: height: " + stackHeight);
        drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            if (stackHeight > 0) {
                super.onBackPressed();
            } else {
                if (stackHeight <= 0 & backPressed + TIME_DELAY > System.currentTimeMillis()) {
                    super.onBackPressed();
                } else {
                    Toast.makeText(MainActivity.this, R.string.press_back_to_exit, Toast.LENGTH_SHORT).show();
                    backPressed = System.currentTimeMillis();
                }
            }
        }
    }

2.Navigation view header in drawer

        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);
        View header = navigationView.getHeaderView(0);
        iv_user = navigationView.findViewById(R.id.iv_user);
        tv_username = navigationView.findViewById(R.id.tv_username);
        String name = new SessionManager(MainActivity.this).getString(Cons.ACCOUNT_NAME);

        Picasso.with(MainActivity.this).load(Cons.BASE_URL).placeholder(R.drawable.ic_profile_new)
                .error(R.drawable.ic_profile_new).into(iv_user);

3. To change title bar name

            ((AppCompatActivity) getActivity()).getSupportActionBar().setTitle(R.string.add_item);