如何在手机处于空闲状态时收集加速度计数据

Question

我目前正在开发一个应用程序，该应用程序应该每两秒钟收集一次加速度计和麦克风数据。为此，我启动了一个服务（在内部运行计时器），以便在应用程序在后台运行时收集数据。到目前为止还不错。

计时器启动、收集数据并将数据写入XML文件。但在查看了生成的XML文件后，我意识到，当手机处于空闲状态时，加速度计的值总是相同的。我甚至用唤醒锁每两秒钟"唤醒"一次手机，但即使这样也不起作用。

这是相关代码：

    @Override
public void onCreate() {
    super.onCreate();
    Toast.makeText(this, "Background Service Created", Toast.LENGTH_SHORT)
            .show();
    Log.d(TAG, "onCreate Service");
    this.startActivities();
}
@Override
public void onDestroy() {
    super.onDestroy();
    // Kill timer, sensors and XML file
    this.stopActivities();
    Toast.makeText(this, "Background Service Stopped", Toast.LENGTH_SHORT)
            .show();
    Log.d(TAG, "onDestroy");
}
@Override
public void onStart(Intent intent, int startid) {
    Toast.makeText(this, "Background Service Started", Toast.LENGTH_SHORT).show();
    Log.d(TAG, "onStart");
}
/**
 * Expanded modification function. 
 */
private void startExpandedNotification(){
    //Id for the intent of the expanded notification
    final int myID = 1234;
    //The intent to launch when the user clicks the expanded notification
    Intent i = new Intent(this, MainMovement.class);
    i.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_SINGLE_TOP);
    PendingIntent pendIntent = PendingIntent.getActivity(this, 0, i, 0);
    //This constructor is deprecated. Use Notification.Builder instead if programming for 3.0+
    Notification notice = new Notification(R.drawable.ic_launcher, "Movement Sampling Activated", System.currentTimeMillis());
    //This method is deprecated. Use Notification.Builder instead if programming for 3.0+
    notice.setLatestEventInfo(this, "Movement Sampling", "Sensors activated", pendIntent);
    notice.flags |= Notification.FLAG_NO_CLEAR;
    startForeground(myID, notice);
}
/**
 * Stop Expanded Notification
 */
private void stopExpandedNotification(){
    stopForeground(true);
}
/**
 * Starts everything that the service needs to collect the sensors data 
 * (timer, xml file, sensors, expanded notification)
 */
private void startActivities() {
    // Define output file path
    OUTPUT_FILE = Environment.getExternalStorageDirectory()
            .getAbsolutePath() + "/Ze";// also added ""/Ze here
    OUTPUT_FILE += "/audiorecordtest.3gp";
    timer = new Timer(); // If I take this line out, it will lead to an
                            // exception. But if I do so, the acc values are
                            // measured while the phone is in the idle state (works only on samsung spika)
    timer.scheduleAtFixedRate(new mainTask(), 0, _refreshRate);
    xml = new DataStore();
    this.startRecordingMic();
    this.startRecordingAcc();
    startExpandedNotification();
    _sampling = true;
}
/**
 * Stops everything that the service needs to collect the sensors data 
 * (timer, xml file, sensors, expanded notification)
 */
private void stopActivities() {
    timer.cancel();
    //Log.e(TAG, "timer: CANCELLED");
    // close xml file
    xml.closeFile();
    //Log.e(TAG, "XML: CLOSED");
    // unregister sensor
    _sensorManager.unregisterListener(accelerationListener);
    //Log.e(TAG, "Sensors: UNREGISTERED");
    // stop recording
    if (_recorder != null) {
        _recorder.stop();
        _recorder.release();
        _recorder = null;
    }
    stopExpandedNotification();
    _sampling = false;
}
/**
 * Responsible for collecting the sensors data every two seconds
 */
private class mainTask extends TimerTask {
    /**
     * Collects the sensor data every 2 seconds
     */
    @Override
    public void run() {
        MovementService.this.collectData();
    }
}
/**
 * Initiates the microphone in order to collect the amplitude value
 */
private void startRecordingMic() {
    _recorder = new MediaRecorder();
    _recorder.setAudioSource(MediaRecorder.AudioSource.MIC);
    _recorder.setOutputFormat(MediaRecorder.OutputFormat.THREE_GPP);
    _recorder.setAudioEncoder(MediaRecorder.AudioEncoder.AMR_NB);
    _recorder.setOutputFile(OUTPUT_FILE);
    try {
        _recorder.prepare();
    } catch (final IllegalStateException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (final IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    _recorder.start();
}
/**
 * Initiates the acceleromenter sensor in order to collect movement data
 */
private void startRecordingAcc() {
    // ACCELEROMETER
    _sensorManager = (SensorManager) this
            .getSystemService(Context.SENSOR_SERVICE);
    _accelerometer = _sensorManager
            .getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
    _sensorManager.registerListener(accelerationListener, _accelerometer,
            SensorManager.SENSOR_DELAY_FASTEST);
}
private final SensorEventListener accelerationListener = new SensorEventListener() {
    public void onAccuracyChanged(Sensor sensor, int acc) {
    }

    public void onSensorChanged(SensorEvent event) {
        // sampling values per axis
        _x = event.values[0];
        _y = event.values[1];
        _z = event.values[2];
        //Log.e(TAG , "x: " + _x + "  y: " + _y + " z:" + _z);
    }
};
/**
 * Send data (amplitude and decibel) to the xml file
 */
public void collectData() {
    //The power lock ensures that the service will indeed collect the accelerometer data
    PowerManager pm = (PowerManager) MovementService.this.getSystemService(Context.POWER_SERVICE);
    PowerManager.WakeLock wl = pm.newWakeLock(PowerManager.FULL_WAKE_LOCK | PowerManager.ACQUIRE_CAUSES_WAKEUP, "YOUR TAG");
    wl.acquire();
    Log.v(TAG, "lock aquired");
    if (xml != null) xml.writeOnFile(this.getAmplitude(), this.getAccelaration(), this.getTotalAccelaration());
    wl.release();
    Log.v(TAG, "lock released");
}

为了解决这个问题，你们有什么建议吗？这简直把我逼疯了。

Ps：我用的是三星spika，安卓2.1版本。

Answer 1

AFAIK当设备空闲时，无法对加速度计进行采样。您需要设置PARTIAL_WAKE_LOCK，以保持CPU运行。它仍然允许屏幕熄灭，但当然，电池会比正常情况下更快耗尽。

http://developer.android.com/reference/android/os/PowerManager.html#PARTIAL_WAKE_LOCK

代码：

PowerManager pm = (PowerManager) getSystemService(Context.POWER_SERVICE);
PowerManager.WakeLock wl = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, "My Tag");
wl.acquire();
//  ..screen will stay on during this section..
wl.release();

您还必须在清单中包括此权限条目：

<uses-permission android:name="android.permission.WAKE_LOCK" /> 

关于这一点，前面有一个问题：如何在后台或睡眠模式下对加速度计数据进行采样