Toolbar – Switching from drawer to back button with only one Activity

Put this code into onCreate() of your Activity. Works well for me. Even using compileSdk 23 and higher.

    drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    final Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    if(toolbar != null) {
        toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        toggle.syncState();
        drawer.setDrawerListener(toggle);
        getSupportFragmentManager().addOnBackStackChangedListener(new FragmentManager.OnBackStackChangedListener() {
            @Override
            public void onBackStackChanged() {
                if (getSupportFragmentManager().getBackStackEntryCount() > 0) {
                    getSupportActionBar().setDisplayHomeAsUpEnabled(true); // show back button
                    toolbar.setNavigationOnClickListener(new View.OnClickListener() {
                        @Override
                        public void onClick(View v) {
                            onBackPressed();
                        }
                    });
                } else {
                    //show hamburger
                    getSupportActionBar().setDisplayHomeAsUpEnabled(false);
                    toggle.syncState();
                    toolbar.setNavigationOnClickListener(new View.OnClickListener() {
                        @Override
                        public void onClick(View v) {
                            drawer.openDrawer(GravityCompat.START);
                        }
                    });
                }
            }
        });