Switch between Fragments with onNavigationItemSelected in new Navigation Drawer Activity template (Android Studio 1.4 onward)

So, based on @L.L.’s answer I was able to solve this problem.

First of all, add your FrameLayout to your content_main.xml file:

<FrameLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent" android:id="@+id/content_frame"/>

In your MainActivity (or whatever you have named the Activity with the navigation drawer) define a method named displayView

 public void displayView(int viewId) {

    Fragment fragment = null;
    String title = getString(R.string.app_name);

    switch (viewId) {
        case R.id.nav_news:
            fragment = new NewsFragment();
            title  = "News";

            break;
        case R.id.nav_events:
            fragment = new EventsFragment();
            title = "Events";
            break;

    }

    if (fragment != null) {
        FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
        ft.replace(R.id.content_frame, fragment);
        ft.commit();
    }

    // set the toolbar title
    if (getSupportActionBar() != null) {
        getSupportActionBar().setTitle(title);
    }

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

}

Am switching between 3 custom Fragments; NewsFragment, EventsFragment and GalleryFragment.

in my menu activity_main_drawer I have changed the content to this:

<menu xmlns:android="http://schemas.android.com/apk/res/android">

<group android:checkableBehavior="single">
    <item android:id="@+id/nav_news"  
        android:icon="@android:drawable/ic_menu_news"
        android:title="News" />
    <item android:id="@+id/nav_events" 
        android:icon="@android:drawable/ic_menu_events"
        android:title="Events" />
    <item android:id="@+id/nav_gallery" 
        android:icon="@android:drawable/ic_menu_gallery"
        android:title="Gallery" />
  </group>
</menu>

Going back to the Activity class, in your onNavigationItemSelected method
do this:

@Override
public boolean onNavigationItemSelected(MenuItem item) {
    displayView(item.getItemId());
    return true;
}

Finally, the last statement in your onCreate method:

 @Override
protected void onCreate(Bundle savedInstanceState) {
    ....
    ....
    displayView(R.id.nav_news);
}

This is because I want the first view my user sees to be News.Change it to whatever you choose.

Handle back press event:

As it stands, if you press the back button from any of the Fragments, the app exits.I want my app to go back to the News Fragment (my home fragment) when the user presses the back button. So I did this:

Declared a boolean variable:

private boolean viewIsAtHome;

then in the displayView() method I did this:

 public void displayView(int viewId){
    Fragment fragment = null;
    String title = getString(R.string.app_name);

    switch (viewId) {
        case R.id.nav_news:
            fragment = new NewsFragment();
            title  = getString(R.string.news_title);
            viewIsAtHome = true;

            break;
        case R.id.nav_events:
            fragment = new EventsFragment();
            title = getString(R.string.events_title);
            viewIsAtHome = false;
            break;

        case R.id.nav_gallery:
            fragment = new GalleryFragment();
            title = getString(R.string.gallery_title);
            viewIsAtHome = false;
            break;

Finally, delete your old onBackPressed method and create a new one like this outside the onCreate() method:

@Override
public void onBackPressed() {
    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    if (drawer.isDrawerOpen(GravityCompat.START)) {
        drawer.closeDrawer(GravityCompat.START);
    }
    if (!viewIsAtHome) { //if the current view is not the News fragment
        displayView(R.id.nav_news); //display the News fragment
    } else {
        moveTaskToBack(true);  //If view is in News fragment, exit application
    }
}

Works for me.