Hamburger Icon not opening Navigation Drawer on parent fragment after returning from child fragment by clicking back arrow on toolbar

Question

The app I am building uses navigation drawer android.support.v4.widget.DrawerLayout and MainActivity extends android.support.v7.app.AppCompatActivity . I have a parent fragment that is replaced by child fragment. On parent fragment default hamburger icon is properly toggling the navigation drawer. While on child fragment, hamburger icon is replaced by back arrow icon using this snippet

((MainActivity)getActivity()).getSupportActionBar().setDisplayHomeAsUpEnabled(true);
toolbar = (Toolbar) (getActivity()).findViewById(R.id.toolbar);
((MainActivity)getActivity()).setSupportActionBar(toolbar);

On child fragment back button click event is handled on onOptionsItemSelected() and hamburger icon is shown again for parent fragment on onStop() .

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
        case android.R.id.home:
            getActivity().onBackPressed();
            return true;
        default:
            return super.onOptionsItemSelected(item);
    }
}

@Override
public void onStop() {
    super.onStop();
    ((MainActivity)getActivity()).getSupportActionBar().setDisplayHomeAsUpEnabled(false);
    MainActivity.toggle.syncState();
}

On parent fragment hamburger icon is now showing properly but on clicking it the navigation drawer doesn't show up again.

Could anyone please help on what am I doing wrong?

Here are the relevant files:

MainActivity.java

public class MainActivity extends AppCompatActivity
    implements NavigationView.OnNavigationItemSelectedListener {
public static ActionBarDrawerToggle toggle;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    try {
        Fragment fragment = (Fragment) ParentFragment.class.newInstance();

        getSupportFragmentManager().beginTransaction().replace(R.id.fragment_content, fragment).commit();
    } catch (InstantiationException e) {
        e.printStackTrace();
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    }

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    toggle = new ActionBarDrawerToggle(
            this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
    drawer.setDrawerListener(toggle);
    toggle.syncState();

    NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
    navigationView.setNavigationItemSelectedListener(this);
}

@Override
public void onBackPressed() {
    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    if (drawer.isDrawerOpen(GravityCompat.START)) {
        drawer.closeDrawer(GravityCompat.START);
    } else {
        super.onBackPressed();
    }
}
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:openDrawer="start">

<include
    layout="@layout/app_bar_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

<android.support.design.widget.NavigationView
    android:id="@+id/nav_view"
    android:layout_width="wrap_content"
    android:layout_height="match_parent"
    android:layout_gravity="start"
    android:fitsSystemWindows="true"
    app:headerLayout="@layout/nav_header_main"
    app:menu="@menu/activity_main_drawer" />

</android.support.v4.widget.DrawerLayout>

ParentFragment.java

public class ParentFragment extends Fragment implements View.OnClickListener {
public static ParentFragment newInstance() {
    ParentFragment fragment = new ParentFragment();
    return fragment;
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setHasOptionsMenu(true);
}

@Override
public void onClick(View v) {
    int i = v.getId();
    Fragment fragment = null;

    if(i == R.id.child_fragment_button) {
        fragment = new ChildFragment();
    } 

    if(fragment != null) {
        FragmentManager fragmentManager = getActivity().getSupportFragmentManager();
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
        fragmentTransaction.replace(R.id.fragment_content, fragment)
                .addToBackStack(null)
                .commit();
    }
}
}

ChildFragment.java

public class ChildFragment extends Fragment { 
private Toolbar toolbar;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setHasOptionsMenu(true);

    // Show back button
    ((MainActivity)getActivity()).getSupportActionBar().setDisplayHomeAsUpEnabled(true);

    toolbar = (Toolbar) (getActivity()).findViewById(R.id.toolbar);
    ((MainActivity)getActivity()).setSupportActionBar(toolbar);
}

@Override
public void onStop() {
    super.onStop();
    ((MainActivity)getActivity()).getSupportActionBar().setDisplayHomeAsUpEnabled(false);
    MainActivity.toggle.syncState();
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
        case android.R.id.home:
            getActivity().onBackPressed();
            return true;
        default:
            return super.onOptionsItemSelected(item);
    }
}
}

Answer 1

I finally came up with the solution. Thanks to this answer .

Here are the changes I made:

ChildFragment.java

public class ChildFragment extends Fragment { 
private Toolbar toolbar;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setHasOptionsMenu(true);

    // Show back button

    toggle = MainActivity.toggle;
    toggle.setDrawerIndicatorEnabled(false);
    toggle.setToolbarNavigationClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            FragmentManager manager = getActivity().getSupportFragmentManager();
            manager.popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);

            toggle.setDrawerIndicatorEnabled(true);
        }
    });

    toolbar = (Toolbar) (getActivity()).findViewById(R.id.toolbar);
    toolbar.setNavigationIcon(((MainActivity)getActivity()).getDrawerToggleDelegate().getThemeUpIndicator());

}

@Override
public void onStop() {
    super.onStop();
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
        default:
            return super.onOptionsItemSelected(item);
    }
}
}