我正在尝试创建一个服务以在 Android 4.2 中运行连续语音识别。使用此链接 (Android Speech Recognition as a service on Android 4.1 & 4.2) 中的答案，我创建了一个从 Activity 运行的服务。我的问题是在 handleMessage 方法中访问 mTarget.mAudioManager 或 mTarget.mSpeechRecognizerIntent 时出现空异常。目标(以及从中创建的 mTarget 对象)不为 null，但其中的所有对象都是。

我在这里做错了什么？

相关Activity代码(从activity调用的静态方法，activityContext就是调用这个方法的activity):

public static void init(Context context)
{
   voiceCommandService = new VoiceCommandService();
   activityContext = context;
}

public static void startContinuousListening()
{
    Intent service = new Intent(activityContext, VoiceCommandService.class);
    activityContext.startService(service);

    Message msg = new Message();
    msg.what = VoiceCommandService.MSG_RECOGNIZER_START_LISTENING; 

    try
    {
      voiceCommandService.mServerMessenger.send(msg);
    } 
    catch (RemoteException e)
   {
    e.printStackTrace();
   }

}

服务代码:

public class VoiceCommandService extends Service
{
protected AudioManager mAudioManager; 
protected SpeechRecognizer mSpeechRecognizer;
protected Intent mSpeechRecognizerIntent;
protected final Messenger mServerMessenger = new Messenger(new IncomingHandler(this));

protected boolean mIsListening;
protected volatile boolean mIsCountDownOn;

static final int MSG_RECOGNIZER_START_LISTENING = 1;
static final int MSG_RECOGNIZER_CANCEL = 2;

@Override
public void onCreate()
{
    super.onCreate();
    mAudioManager = (AudioManager) getSystemService(Context.AUDIO_SERVICE); 
    mSpeechRecognizer = SpeechRecognizer.createSpeechRecognizer(this);
    mSpeechRecognizer.setRecognitionListener(new SpeechRecognitionListener());
    mSpeechRecognizerIntent = new Intent(RecognizerIntent.ACTION_RECOGNIZE_SPEECH);
    mSpeechRecognizerIntent.putExtra(RecognizerIntent.EXTRA_LANGUAGE_MODEL,
                                     RecognizerIntent.LANGUAGE_MODEL_FREE_FORM);
    mSpeechRecognizerIntent.putExtra(RecognizerIntent.EXTRA_CALLING_PACKAGE,
                                     this.getPackageName());
}

protected static class IncomingHandler extends Handler
{
    private WeakReference<VoiceCommandService> mtarget;

    IncomingHandler(VoiceCommandService target)
    {
        mtarget = new WeakReference<VoiceCommandService>(target);
    }


    @Override
    public void handleMessage(Message msg)
    {
        final VoiceCommandService target = mtarget.get();

        switch (msg.what)
        {
            case MSG_RECOGNIZER_START_LISTENING:

                if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN)
                {
                    // turn off beep sound  
                    target.mAudioManager.setStreamMute(AudioManager.STREAM_SYSTEM, true);
                }
                 if (!target.mIsListening)
                 {
                     target.mSpeechRecognizer.startListening(target.mSpeechRecognizerIntent);
                     target.mIsListening = true;
                    //Log.d(TAG, "message start listening"); //$NON-NLS-1$
                 }
                 break;

             case MSG_RECOGNIZER_CANCEL:
                  target.mSpeechRecognizer.cancel();
                  target.mIsListening = false;
                  //Log.d(TAG, "message canceled recognizer"); //$NON-NLS-1$
                  break;
         }
   } 
} 

// Count down timer for Jelly Bean work around
protected CountDownTimer mNoSpeechCountDown = new CountDownTimer(5000, 5000)
{

    @Override
    public void onTick(long millisUntilFinished)
    {
        // TODO Auto-generated method stub

    }

    @Override
    public void onFinish()
    {
        mIsCountDownOn = false;
        Message message = Message.obtain(null, MSG_RECOGNIZER_CANCEL);
        try
        {
            mServerMessenger.send(message);
            message = Message.obtain(null, MSG_RECOGNIZER_START_LISTENING);
            mServerMessenger.send(message);
        }
        catch (RemoteException e)
        {

        }
    }
};

@Override
public void onDestroy()
{
    super.onDestroy();

    if (mIsCountDownOn)
    {
        mNoSpeechCountDown.cancel();
    }
    if (mSpeechRecognizer != null)
    {
        mSpeechRecognizer.destroy();
    }
}

protected class SpeechRecognitionListener implements RecognitionListener
{

    private static final String TAG = "SpeechRecognitionListener";

    @Override
    public void onBeginningOfSpeech()
    {
        // speech input will be processed, so there is no need for count down anymore
        if (mIsCountDownOn)
        {
            mIsCountDownOn = false;
            mNoSpeechCountDown.cancel();
        }               
        //Log.d(TAG, "onBeginingOfSpeech"); //$NON-NLS-1$
    }

    @Override
    public void onBufferReceived(byte[] buffer)
    {

    }

    @Override
    public void onEndOfSpeech()
    {
        //Log.d(TAG, "onEndOfSpeech"); //$NON-NLS-1$
     }

    @Override
    public void onError(int error)
    {
        if (mIsCountDownOn)
        {
            mIsCountDownOn = false;
            mNoSpeechCountDown.cancel();
        }
         mIsListening = false;
         Message message = Message.obtain(null, MSG_RECOGNIZER_START_LISTENING);
         try
         {
                mServerMessenger.send(message);
         }
         catch (RemoteException e)
         {

         }
        //Log.d(TAG, "error = " + error); //$NON-NLS-1$
    }

    @Override
    public void onEvent(int eventType, Bundle params)
    {

    }

    @Override
    public void onPartialResults(Bundle partialResults)
    {

    }

    @Override
    public void onReadyForSpeech(Bundle params)
    {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN)
        {
            mIsCountDownOn = true;
            mNoSpeechCountDown.start();
            mAudioManager.setStreamMute(AudioManager.STREAM_SYSTEM, false);
        }
        Log.d(TAG, "onReadyForSpeech"); //$NON-NLS-1$
    }

    @Override
    public void onResults(Bundle results)
    {
        //Log.d(TAG, "onResults"); //$NON-NLS-1$

    }

    @Override
    public void onRmsChanged(float rmsdB)
    {

    }

}

@Override
public IBinder onBind(Intent arg0) {
    // TODO Auto-generated method stub
    return null;
}
}

最佳答案

MainActivity 中的类成员

private int mBindFlag;
private Messenger mServiceMessenger;

在onCreate()中启动服务

@Override
protected void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);

    Intent service = new Intent(activityContext, VoiceCommandService.class);
    activityContext.startService(service);
    mBindFlag = Build.VERSION.SDK_INT < Build.VERSION_CODES.ICE_CREAM_SANDWICH ? 0 : Context.BIND_ABOVE_CLIENT;

}

在onStart()中绑定(bind)服务

@Override
protected void onStart()
{
    super.onStart();

    bindService(new Intent(this, VoiceCommandService.class), mServiceConnection, mBindFlag);
}

@Override
protected void onStop()
{
    super.onStop();

    if (mServiceMessenger != null)
    {
        unbindService(mServiceConnection);
        mServiceMessenger = null;
    }
}

mServiceConnection成员

private final ServiceConnection mServiceConnection = new ServiceConnection()
{
    @Override
    public void onServiceConnected(ComponentName name, IBinder service)
    {
        if (DEBUG) {Log.d(TAG, "onServiceConnected");} //$NON-NLS-1$

        mServiceMessenger = new Messenger(service);
        Message msg = new Message();
        msg.what = VoiceCommandService.MSG_RECOGNIZER_START_LISTENING; 

        try
        {
            mServiceMessenger.send(msg);
        } 
        catch (RemoteException e)
        {
            e.printStackTrace();
        }
    }

    @Override
    public void onServiceDisconnected(ComponentName name)
    {
        if (DEBUG) {Log.d(TAG, "onServiceDisconnected");} //$NON-NLS-1$
        mServiceMessenger = null;
    }

}; // mServiceConnection

在服务中

@Override
public IBinder onBind(Intent intent)
{
    Log.d(TAG, "onBind");  //$NON-NLS-1$

    return mServerMessenger.getBinder();
}

关于Android语音识别持续服务，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/18039429/