HMT Development Examples

Development Example – Speech Recognizer

Voice commands can be added to an application by updating the resource files, but it’s also possible to add them in the source code if required.

Registering voice commands

Voice commands can be registered by sending a list to WearHF using an intent:

 private static final String ACTION_OVERRIDE = 

private static final String EXTRA_COMMANDS =
private static final String EXTRA_SOURCE =

private void sendCommands() {
final ArrayList<String> voiceCommands = new ArrayList<>(); 
voiceCommands.add("Command 1"); 
voiceCommands.add("Command 2"); 

Intent intent = new Intent(ACTION_OVERRIDE_COMMANDS); 
intent.putExtra(EXTRA_SOURCE_PACKAGE, getPackageName()); 
intent.putExtra(EXTRA_COMMANDS, commands); 

Once registered WearHF will listen for the provided commands until:

  1. A voice command is spoken.
  2. The user presses the ACTION button, which will take the system to the home screen.
  3. The current application exits.
  4. A new OVERRIDE_COMMANDS action is preformed.
  5. A RESTORE_COMMANDS action is preformed.
  6. Once one of these events has occurred the application must re-register it’s voice commands.

It’s important to note that using the OVERRIDE_COMMANDS action will prevent WearHF from recognizing scripted or embedded WearML commands.

Reacting to voice command triggers

Applications can listen for when the speech recognizer has detected a spoken voice command by using a broadcast listener:

 private static final String ACTION_SPEECH_EVENT = "com.realwear.wearhf.intent.action.SPEECH_EVENT"; 
private static final String EXTRA_COMMAND = "com.realwear.wearhf.intent.extra.COMMAND";
private static final String EXTRA_ORIG_COMMAND = "com.realwear.wearhf.intent.extra.ORIGINAL_COMMAND";
private static final String EXTRA_CONFIDENCE = "com.realwear.wearhf.intent.extra.CONFIDENCE";

private BroadcastReceiver speechBroadcastReceiver = new BroadcastReceiver() {
public void onReceive(Context context, Intent intent) { 
if (intent.getAction().equals(ACTION_SPEECH_EVENT)) { 
String command = intent.getStringExtra(EXTRA_COMMAND); 

Restore normal services

When an application has finished with the speech recognizer it should send a message to restore default behaviour, using the RESTORE_COMMANDS intent.

 private static final String ACTION_RESTORE = 

private void restoreVoiceCommands() {
Intent intent = new Intent(ACTION_RESTORE); 

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Handling Lifecycle Events

When an application registers voice commands right after launching or resuming, there will sometimes be a race condition between the Speech Recognizer and the automatic UI parser provided by WearHF. This can result in any override commands defined by the developer to be ignored. Make sure to include a short delay if you register commands in Lifecycle functions such as onCreate or onResume.

protected void onResume() {

registerReceiver(asrBroadcastReceiver, new IntentFilter(ACTION_SPEECH_EVENT));

new Handler().postDelayed(new Runnable() {
public void run() {
}, 100);

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Intent Description
com.realwear.wearhf.intent.action.OVERRIDE_COMMANDS Used to take control of the speech recognizer
com.realwear.wearhf.intent.action.RESTORE_COMMANDS Used to reset the speech recognizer to it’s default behavior
com.realwear.wearhf.intent.action.SPEECH_EVENT Sent from WearHF to identify spoken voice commands


Extra Data Type Description
com.realwear.wearhf.intent.extra.COMMANDS String Array Used to pass in a list of voice commands to the speech recognizer
com.realwear.wearhf.intent.extra.SOURCE_PACKAGE String Used to pass the application’s package name to the speech recognizer
com.realwear.wearhf.intent.extra.GLOBAL_COMMANDS boolean Specifies whether the speech recognizer should also listen for the global commands
com.realwear.wearhf.intent.extra.ACTION_BUTTON_HOME boolean Specifies whether the ACTION button should be used as a way to exit the application and go to home screen
com.realwear.wearhf.intent.extra.COMMAND String Passed from the speech recognizer when a voice command is spoken. Identifies the command spoken by the user
com.realwear.wearhf.intent.extra.ORIGINAL_COMMAND String Passed from the speech recognizer when a voice command is spoken. Identifies the command spoken by the user, but may be stripped of extra whitespace or unwanted characters
com.realwear.wearhf.intent.extra.CONFIDENCE int The confidence level reported by the speech recognizer. The higher the confidence, the more closely the spoken words matched the returned phrase (ranges 4000-8000, where higher is better).