如何在Android中也保持后台运行前台服务

Question

I want to make an app turn on/off by shaking while screen locked as well as background, below is my code that runs only for foreground can you help me that how can foreground service can continue in background.

MainActivty.java

public class Torchclass extends Activity {

   // The following are used for the shake detection
private SensorManager mSensorManager;
private Sensor mAccelerometer;
private ShakeDetector mShakeDetector;
public static Camera cam = null;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.torchlayout);

    Intent intent = new Intent(Torchclass.this, ShakeService.class);
    startService(intent);

    // ShakeDetector initialization
    mSensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
    mAccelerometer = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
    mShakeDetector = new ShakeDetector();
    mShakeDetector.setOnShakeListener(new ShakeDetector.OnShakeListener() {

        @Override
        public void onShake(int count) {
            try {
                if (getPackageManager().hasSystemFeature(
                        PackageManager.FEATURE_CAMERA_FLASH)) {
                    cam = Camera.open();
                    Parameters p = cam.getParameters();
                    p.setFlashMode(Parameters.FLASH_MODE_TORCH);
                    cam.setParameters(p);
                    cam.startPreview();
                }
            } catch (Exception e) {

                e.printStackTrace();
                Toast.makeText(getBaseContext(), "Exception flashLightOn()",
                        Toast.LENGTH_SHORT).show();

                if (getPackageManager().hasSystemFeature(
                        PackageManager.FEATURE_CAMERA_FLASH)) {
                    cam.stopPreview();
                    cam.release();
                    cam = null;
                }
            }

        }
    });
}

@Override
public void onResume() {
    super.onResume();
    // Add the following line to register the Session Manager Listener onResume
    mSensorManager.registerListener(mShakeDetector, mAccelerometer, SensorManager.SENSOR_DELAY_UI);
}

@Override
public void onPause() {
    // Add the following line to unregister the Sensor Manager onPause
      mSensorManager.registerListener(mShakeDetector, mAccelerometer, SensorManager.SENSOR_DELAY_UI);

    super.onPause();
}
}

ShakeDetector.java

public class ShakeDetector implements SensorEventListener {

/*
 * The gForce that is necessary to register as shake.
 * Must be greater than 1G (one earth gravity unit).
 * You can install "G-Force", by Blake La Pierre
 * from the Google Play Store and run it to see how
 *  many G's it takes to register a shake
 */
private static final float SHAKE_THRESHOLD_GRAVITY = 2.7F;
private static final int SHAKE_SLOP_TIME_MS = 500;
private static final int SHAKE_COUNT_RESET_TIME_MS = 3000;

private OnShakeListener mListener;
private long mShakeTimestamp;
private int mShakeCount;

public void setOnShakeListener(OnShakeListener listener) {
    this.mListener = listener;
}

public interface OnShakeListener {
    public void onShake(int count);
}

@Override
public void onAccuracyChanged(Sensor sensor, int accuracy) {
    // ignore
}

@Override
public void onSensorChanged(SensorEvent event) {

    if (mListener != null) {
        float x = event.values[0];
        float y = event.values[1];
        float z = event.values[2];

        float gX = x / SensorManager.GRAVITY_EARTH;
        float gY = y / SensorManager.GRAVITY_EARTH;
        float gZ = z / SensorManager.GRAVITY_EARTH;

        // gForce will be close to 1 when there is no movement.
        Float f = new Float(gX * gX + gY * gY + gZ * gZ);
        Double d = Math.sqrt(f.doubleValue());
        float gForce = d.floatValue();

        if (gForce > SHAKE_THRESHOLD_GRAVITY) {
            final long now = System.currentTimeMillis();
            // ignore shake events too close to each other (500ms)
            if (mShakeTimestamp + SHAKE_SLOP_TIME_MS > now) {
                return;
            }

            // reset the shake count after 3 seconds of no shakes
            if (mShakeTimestamp + SHAKE_COUNT_RESET_TIME_MS < now) {
                mShakeCount = 0;
            }

            mShakeTimestamp = now;
            mShakeCount++;

            mListener.onShake(mShakeCount);
        }
    }
}
} 

ShakeService.java

public class ShakeService extends Service {

private SensorManager mSensorManager;
private Sensor mAccelerometer;
private ShakeDetector mShakeDetector;

public ShakeService() {
}

@Override
public IBinder onBind(Intent intent) {
    // TODO: Return the communication channel to the service.
    throw new UnsupportedOperationException("Not yet implemented");
}

@Override
public void onCreate() {
    super.onCreate();
    // ShakeDetector initialization
    mSensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
    mAccelerometer = mSensorManager
            .getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
    mShakeDetector = new ShakeDetector();
    mShakeDetector.setOnShakeListener(new ShakeDetector.OnShakeListener() {

        @Override
        public void onShake(int count) {

            Intent i = getApplicationContext().getPackageManager().getLaunchIntentForPackage("com.facebook.katana");
            getApplicationContext().startActivity(i);

        }
    });
    mSensorManager.registerListener(mShakeDetector, mAccelerometer, SensorManager.SENSOR_DELAY_UI);
}

@Override
public void onDestroy() {
     mSensorManager.registerListener(mShakeDetector, mAccelerometer, SensorManager.SENSOR_DELAY_UI);

    super.onDestroy();
}
}

Answer 1

you should override onStartCommand method in service:

public int onStartCommand(Intent intent, int flags, int startId) {
{
return START_STICKY
}