How to set a default fragment in Android Studio Navigation Drawer?

Question

I'm looking for a way to se a default fragment in my navigation drawer which is not the item # 0. I've seen some solutions based on checking if savedInstanceState is null or not but I feel like I don't have access to this in my onNavigationDrawerItemSelected method. Here is my class:

public class Main extends ActionBarActivity
    implements NavigationDrawerFragment.NavigationDrawerCallbacks {

/**
 * Fragment managing the behaviors, interactions and presentation of the navigation drawer.
 */
private NavigationDrawerFragment mNavigationDrawerFragment;

/**
 * Used to store the last screen title. For use in {@link #restoreActionBar()}.
 */
private CharSequence mTitle;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    mNavigationDrawerFragment = (NavigationDrawerFragment)
            getSupportFragmentManager().findFragmentById(R.id.navigation_drawer);
    mTitle = getTitle();

    // Set up the drawer.
    mNavigationDrawerFragment.setUp(
            R.id.navigation_drawer,
            (DrawerLayout) findViewById(R.id.drawer_layout));
}

@Override
public void onNavigationDrawerItemSelected(int position) {
    // update the Main content by replacing fragments
    Fragment fragment = null;
    switch (position) {
        case 0:
            fragment = new HomeFragment();
            break;
        case 1:
            fragment = new HomeFragment();
            break;
        case 2:
            fragment = new HomeFragment();
            break;
        default:
            fragment = new DiscoverFragment();
    }


    if (fragment != null) {
        FragmentManager fragmentManager = getSupportFragmentManager();
        fragmentManager.beginTransaction()
                .replace(R.id.container, fragment).commit();

    }

}

Answer 1

The answer is rather simple. Since the DrawerLayout leaves you to manage fragments on your own, you can just use the basic FragmentManager APIs that would be used in a normal FragmentActivity.

I use the following method to make it a little simpler, which will replace the current fragments even if there are none currently added to the container. Just call this method with the fragment you want to be default in your onCreate() method.

public void setFragment(Fragment fragment) {
    FragmentManager fragmentManager = getSupportFragmentManager();
    fragmentManager.beginTransaction()
                   .replace(R.id.container, fragment)
                   .commit();
}

Note that it is technically more correct to use .add(fragment) for the first call rather than .replace since you aren't replacing anything, but it really doesn't matter because internally, it basically just removes any existing fragments and adds the new one using .add() for you http://developer.android.com/reference/android/app/FragmentTransaction.html#replace(int,android.app.Fragment,java.lang.String)