How to detect key events in service and broadcast receiver

Question

How can I get key events when a user presses various buttons in a service or broadcast receiver? I'm specifically interested in knowing when the user presses a volume button so that I can trigger something else in the background, like a voice recorder.

Unfortunately, my internet searches haven't produced any results.

Answer 1

Something like the following should work:
From official documentation:

<application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"...>
    //code, like activities, etc

    <receiver android:name="com.example.test.VolumeBroadcast" >
        <intent-filter>
           <action android:name="android.intent.action.MEDIA_BUTTON" />
        </intent-filter>
</application>

Example of a receiver:

  public class VolumeBroadcast extends BroadcastReceiver{

      public void onReceive(Context context, Intent intent) {
           //check the intent something like:
           if (Intent.ACTION_MEDIA_BUTTON.equals(intent.getAction())) {
              KeyEvent event = (KeyEvent)intent.getParcelableExtra(Intent.EXTRA_KEY_EVENT);
              if (KeyEvent.KEYCODE_MEDIA_PLAY == event.getKeyCode()) {
                 // Handle key press.
              }
           }
      }
  }

The way you register is like that:

 AudioManager am = mContext.getSystemService(Context.AUDIO_SERVICE);
// Start listening for button presses
am.registerMediaButtonEventReceiver(RemoteControlReceiver); 
// Stop listening for button presses
am.unregisterMediaButtonEventReceiver(RemoteControlReceiver);

Page below:
Audio Playback