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

Question

IntelliJ has made changes to the Navigation Drawer template Activity in Android Studio with fewer lines of code in the Activity class. The new Activity class looks like this:

public class MainActivity extends AppCompatActivity
    implements NavigationView.OnNavigationItemSelectedListener {

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

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();
        }
    });

    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);
}

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


@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
    // Handle navigation view item clicks here.
    int id = item.getItemId();

    if (id == R.id.nav_camara) {
        // Handle the camera action
    } else if (id == R.id.nav_gallery) {

    } else if (id == R.id.nav_slideshow) {

    } else if (id == R.id.nav_manage) {

    } else if (id == R.id.nav_share) {

    } else if (id == R.id.nav_send) {

    }

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

One of the most notable change here is the method:

onNavigationItemSelected(MenuItem item)

The old Navigation Drawer template's definition of this method was:

onNavigationItemSelected(int position, long itemId)

You could modify that old template by deleting the inner PlaceHolderFragment class, creating your own fragments and layouts and doing something like this:

Fragment fragment = null;
switch (position) {
    case 0:
        fragment = new FragmentA();
        break;
    case 1:
        fragment = new FragmentB();
        break;
    default:
        break;
}

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

}

But this doesn't work with the new template (at least not from my little knowledge). I have tried:

 public boolean onNavigationItemSelected(MenuItem item) {
    // Handle navigation view item clicks here.
    int id = item.getItemId();
    Snackbar snackbar = Snackbar.make(findViewById(android.R.id.content), item.getTitle() + " clicked", Snackbar.LENGTH_SHORT);
    Fragment fragment = null;
    switch (id) {
        case R.id.nav_home:
            fragment = HomeFragment.getFragInstance();
            break;

        case R.id.nav_news:

            fragment = NewsFragment.getFragInstance();
            break;


        default:
            break;
    }

    if (fragment != null) {
        FragmentTransaction transaction = fragmentManager.beginTransaction();
        transaction.addToBackStack(null);
        transaction.replace(R.id.drawer_layout, fragment);
        transaction.commit();


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

    }
    return true;
}

but the layout for the home layout is also shown in the news layout. This is probably happening because of the line:

transaction.replace(R.id.drawer_layout, fragment);

Fragments are supposed to be replaced in a FrameLayout and the old Navigation Drawer layout looked like this:

<android.support.v4.widget.DrawerLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent">

<!-- Framelayout to display Fragments -->
<FrameLayout
    android:id="@+id/frame_container"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

<!-- Listview to display slider menu -->


<ListView
    android:id="@+id/list_sliderMenu"
    android:layout_width="240dp"
    android:layout_height="match_parent"
    android:layout_gravity="start"
    android:choiceMode="singleChoice"
    android:divider="@color/white"
    android:dividerHeight="1dp"
    android:listSelector="@drawable/list_selector"
    android:background="@color/list_background"/>

But the new one looks like this:

 <?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_base"
    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_base"
    app:menu="@menu/activity_base_drawer" />

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

Long story short, how can one modify the new template to be able to switch between Fragments?

Answer 1

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.