在android中使用VoiceInteractionService的HotwordDetector

我正在使用自定义命令创建语音识别服务，例如“Ok Google”。为此我使用了VoiceInteractionService我引用了代码here http://androidxref.com/5.0.0_r2/xref/frameworks/base/tests/VoiceInteraction/src/com/android/test/voiceinteraction/。另外，我得到了STATE_HARDWARE_UNAVAILABLE错误于onAvailabilityChanged.

public class VoiceCommandService extends VoiceInteractionService {
private static final String TAG = "AlwaysOnHotwordDetector";
Locale locale = new Locale("en-US");
protected SpeechRecognizer mSpeechRecognizer;
protected Intent mSpeechRecognizerIntent;

public final Callback mHotwordCallback = new Callback() {
    @Override
    public void onAvailabilityChanged(int status) {
        Log.i(TAG, "onAvailabilityChanged(" + status + ")");
        hotwordAvailabilityChangeHelper(status);
    }

    @Override
    public void onDetected(EventPayload eventPayload) {
        Log.i(TAG, "onDetected");
    }

    @Override
    public void onError() {
        Log.i(TAG, "onError");
    }

    @Override
    public void onRecognitionPaused() {
        Log.i(TAG, "onRecognitionPaused");
    }

    @Override
    public void onRecognitionResumed() {
        Log.i(TAG, "onRecognitionResumed");
    }
};

private AlwaysOnHotwordDetector mHotwordDetector;

@Override
public void onCreate(){
    Log.d(TAG, "Entered on create");
    super.onCreate();
}

@Override
public void onReady() {
    super.onReady();
    Log.i(TAG, "Creating " + this);
    mHotwordDetector = createAlwaysOnHotwordDetector(
            "Hello", Locale.forLanguageTag("en-US"), mHotwordCallback);
}

@Override
public int onStartCommand(Intent intent, int flags, int startId) {
    Bundle args = new Bundle();
    args.putParcelable("intent", new Intent(this, MainActivity.class));
    showSession(args, 0);
    stopSelf(startId);
    return START_NOT_STICKY;
}

private void hotwordAvailabilityChangeHelper(int availability) {
    Log.i(TAG, "Hotword availability = " + availability);
    switch (availability) {
        case AlwaysOnHotwordDetector.STATE_HARDWARE_UNAVAILABLE:
            Log.i(TAG, "STATE_HARDWARE_UNAVAILABLE");
            break;
        case AlwaysOnHotwordDetector.STATE_KEYPHRASE_UNSUPPORTED:
            Log.i(TAG, "STATE_KEYPHRASE_UNSUPPORTED");
            break;
        case AlwaysOnHotwordDetector.STATE_KEYPHRASE_UNENROLLED:
            Log.i(TAG, "STATE_KEYPHRASE_UNENROLLED");
            Intent enroll = mHotwordDetector.createEnrollIntent();
            Log.i(TAG, "Need to enroll with " + enroll);
            break;
        case AlwaysOnHotwordDetector.STATE_KEYPHRASE_ENROLLED:
            Log.i(TAG, "STATE_KEYPHRASE_ENROLLED - starting recognition");
            if (mHotwordDetector.startRecognition(0)) {
                Log.i(TAG, "startRecognition succeeded");
            } else {
                Log.i(TAG, "startRecognition failed");
            }
            break;
    }
}}

VoiceInteractionService need android.permission.BIND_VOICE_INTERACTION in AndroidManifests