Copy code from the NumbersActivity and paste it into the NumbersFragment

Code to go into NumberFragment.java

/** Handles playback of all the sound files */
private MediaPlayer mMediaPlayer;

/** Handles audio focus when playing a sound file */
private AudioManager mAudioManager;

/**
* This listener gets triggered whenever the audio focus changes
* (i.e., we gain or lose audio focus because of another app or device).
*/
private AudioManager.OnAudioFocusChangeListener mOnAudioFocusChangeListener = new AudioManager.OnAudioFocusChangeListener() {
   @Override
   public void onAudioFocusChange(int focusChange) {
       if (focusChange == AudioManager.AUDIOFOCUS_LOSS_TRANSIENT ||
               focusChange == AudioManager.AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK) {
           // The AUDIOFOCUS_LOSS_TRANSIENT case means that we've lost audio focus for a
           // short amount of time. The AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK case means that
           // our app is allowed to continue playing sound but at a lower volume. We'll treat
           // both cases the same way because our app is playing short sound files.

           // Pause playback and reset player to the start of the file. That way, we can
           // play the word from the beginning when we resume playback.
           mMediaPlayer.pause();
           mMediaPlayer.seekTo(0);
       } else if (focusChange == AudioManager.AUDIOFOCUS_GAIN) {
           // The AUDIOFOCUS_GAIN case means we have regained focus and can resume playback.
           mMediaPlayer.start();
       } else if (focusChange == AudioManager.AUDIOFOCUS_LOSS) {
           // The AUDIOFOCUS_LOSS case means we've lost audio focus and
           // Stop playback and clean up resources
           releaseMediaPlayer();
       }
   }
};

/**
* This listener gets triggered when the {@link MediaPlayer} has completed
* playing the audio file.
*/
private MediaPlayer.OnCompletionListener mCompletionListener = new MediaPlayer.OnCompletionListener() {
   @Override
   public void onCompletion(MediaPlayer mediaPlayer) {
       // Now that the sound file has finished playing, release the media player resources.
       releaseMediaPlayer();
   }
};

NumberFragments.java can be found here :) https://github.com/udacity/ud839_Miwok/blob/d7effcef3bf7fdccdd045c974d67abd5b960fae7/app/src/main/java/com/example/android/miwok/NumbersFragment.java

Great how this helps many more over the years

many years

I am getting null pointer exception on adapter reference of WordAdapter class which we created when calling method ListView.setAdapter

WordAdapter itemsAdapter = new WordAdapter(getActivity(), words, R.color.category_numbers);
//ListView listView = findViewById(R.id.list);
ListView listView = (ListView) rootView.findViewById(R.id.list);
listView.setAdapter(itemsAdapter);