Need clarification on how to launch activity and view one of the fragments

Question

The almost-solution is How to launch activity and show specific fragment but I unable to connect the dots on how to solve it.

The MainActivity.java have navigation drawer with few fragments. In StudentFragment (since no logged in user, only view login button), I launched a login activity via a button. The login is fine and view user profile, but when I press back to go back to StudentFragment , the layout won't update. It should view a layout for logged in user. In order to view it, I have to close and open the app again.

To tackle this problem, I was thinking on how to relaunch MainActivity with viewing StudentFragment by clear the top stack.

The second answer in link can be use as solution but I need more explanation of it :(

My codes:

MainActivity.java

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

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    ActionBarDrawerToggle 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);

    // view layout home here
    Fragment fragment = new HomeFragment();
    FragmentManager fragmentManager = getSupportFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
    fragmentTransaction.replace(R.id.container_body, fragment);
    fragmentTransaction.commit();
}


public boolean onNavigationItemSelected(MenuItem item) {
    // Handle navigation view item clicks here.

    Fragment fragment = null;

    int id = item.getItemId();

    if (id == R.id.nav_home) {
        // Handle the home action
        fragment = new HomeFragment();

    } else if (id == R.id.nav_outline) {
        fragment = new OutlineFragment();
        getSupportActionBar().setTitle("Course Outline");

    } else if (id == R.id.nav_PDPA) {
        fragment = new PDPAFragment();
        getSupportActionBar().setTitle("PDPA 2010");

    } else if (id == R.id.nav_copyright) {
        fragment = new CopyrightFragment();
        getSupportActionBar().setTitle("Copyright Act 2012");

    } else if (id == R.id.nav_laws) {
        fragment = new LawsFragment();
        getSupportActionBar().setTitle("List of Laws");

    } else if (id == R.id.nav_students) {
        fragment = new StudentsFragment();
        getSupportActionBar().setTitle("Student");
    } else if (id == R.id.nav_lecturers) {
        fragment = new LecturerFragment();
        getSupportActionBar().setTitle("Lecturer");
    }

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

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    drawer.closeDrawer(GravityCompat.START);
    return true;
}

EDIT by following Sanjeet answer

In LoginActivity

Intent intent = new Intent(LoginActivity.this, MainActivity.class);
                setResult(Config.RESULT_CODE, intent);
                intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                startActivity(intent);

In MainActivity

@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (resultCode == Config.RESULT_CODE && requestCode == Config.REQUEST_CODE) {

        Fragment frg = null;
        frg = getSupportFragmentManager().findFragmentById(R.id.nav_students);
        final FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
        ft.detach(frg);
        ft.attach(frg);
        ft.commit();
    }
}

But the fragment shown after relaunch MainActivity is HomeFragment , not StudentFragment .

Answer 1

Start the Login Activity using

startActivityForResult(intent, REQUEST_CODE);

Now, after successful login set the result and finish the Login activity after setting the result code.

Intent intent = new Intent();
setResult(RESULT_CODE, intent);
finish();

Now in your MainActivity's class onActivityResult() based on REQUEST_CODE and RESULT_CODE restart your Student Fragment.

@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (resultCode == RESULT_CODE && requestCode == REQUEST_CODE) {

            Fragment frg = null;
            frg = getSupportFragmentManager().findFragmentByTag("Your_Fragment_TAG");
            final FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
            ft.detach(frg);
            ft.attach(frg);
            ft.commit();

    }

}