Navigation Drawer back button in fragments

setNavigationOnClick() on the toolbar after setSupportActionBar(toolbar) :

setSupportActionBar(toolbar);
toolbar.setNavigationOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View view) {
                Toast.makeText(getActivity(), "Back clicked!",     
                Toast.LENGTH_SHORT).show();
            }
        });

I have made a small app for reference

FirstFragment

 public class FirstFragment extends Fragment {


public FirstFragment() {
    // Required empty public constructor
}


@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    return inflater.inflate(R.layout.fragment_first, container, false);
}

}

SecondFragment

public class SecondFragment extends Fragment {


public SecondFragment() {
    // Required empty public constructor
}


@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    return inflater.inflate(R.layout.fragment_second, container, false);
}

}

MainActivity

public class MainActivity extends AppCompatActivity {
private Toolbar mToolbar;
private ActionBarDrawerToggle drawerToggle;
private DrawerLayout mDrawerLayout;
private String TAG = "MainActivity";
private FragmentManager mFragmentManager;
private NavigationView mNavigationView;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    mToolbar = (Toolbar) findViewById(R.id.toolbar);
    if (mToolbar != null) {
        setSupportActionBar(mToolbar);
    }
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);

    mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer);
    drawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout, R.string.drawer_open, R.string.drawer_close) {
        @Override
        public void onDrawerOpened(View drawerView) {
            super.onDrawerOpened(drawerView);
        }

        @Override
        public void onDrawerClosed(View drawerView) {
            super.onDrawerClosed(drawerView);
        }
    };
    mDrawerLayout.addDrawerListener(drawerToggle);
    mNavigationView = findViewById(R.id.navigation);
    mNavigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem item) {
            switch (item.getItemId()) {
                case R.id.first:
                    changeFragment(new FirstFragment(), true);
                    return true;
                case R.id.second:
                    changeFragment(new SecondFragment(), true);
                    return true;
            }
            return false;
        }
    });
    mFragmentManager = getSupportFragmentManager();
    changeFragment(new FirstFragment(), true);
}

@Override
protected void onPostCreate(@Nullable Bundle savedInstanceState) {
    super.onPostCreate(savedInstanceState);
    if (drawerToggle != null) {
        drawerToggle.syncState();
    }
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    if (item.getItemId() == android.R.id.home) {
        Log.i(TAG, "onOptionsItemSelected: Home Button Clicked");
        if (mDrawerLayout.isDrawerOpen(Gravity.START)) {
            mDrawerLayout.closeDrawer(Gravity.START);
        } else {
            mDrawerLayout.openDrawer(Gravity.START);
        }
    }
    return super.onOptionsItemSelected(item);
}

@Override
public void onBackPressed() {
    if (mDrawerLayout.isDrawerOpen(Gravity.START)) {
        mDrawerLayout.closeDrawer(Gravity.START);
    }
    if (mDrawerLayout.isDrawerOpen(Gravity.START)) {
        mDrawerLayout.closeDrawer(Gravity.START);
    } else if (mFragmentManager.getBackStackEntryCount() > 0) {
        mFragmentManager.popBackStack();
    } else {
        super.onBackPressed();
    }
}

private void changeFragment(Fragment fragment, boolean needToAddBackstack) {
    FragmentTransaction mFragmentTransaction = mFragmentManager.beginTransaction();
    mFragmentTransaction.replace(R.id.FRAME_CONTENT, fragment);
    mFragmentTransaction.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
    if (needToAddBackstack)
        mFragmentTransaction.addToBackStack(null);
    mFragmentTransaction.commit();
}
}

activity_main

<FrameLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent">
            

    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="@dimen/abc_action_bar_default_height_material"
        android:background="@color/colorPrimaryDark"
        />

    <FrameLayout
        android:id="@+id/FRAME_CONTENT"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginTop="@dimen/abc_action_bar_default_height_material" />
</FrameLayout>

<android.support.design.widget.NavigationView
    android:id="@+id/navigation"
    android:layout_width="wrap_content"
    android:layout_height="match_parent"
    android:layout_gravity="start"
    android:layout_marginTop="@dimen/abc_action_bar_default_height_material"
    app:menu="@menu/drawermenu" />
  </android.support.v4.widget.DrawerLayout>

I had the same issue.

I finally solved 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);
            }else{
                drawer.setDrawerLockMode(DrawerLayout.LOCK_MODE_LOCKED_CLOSED);
                menuToggle.setDrawerIndicatorEnabled(false);

            }
        }
    });

Hope it helps