如何在安卓中保持后台运行前台服务

Question

我想通过在屏幕锁定和后台时摇晃来打开/关闭应用程序，下面是我仅在前台运行的代码，您能否帮助我如何在后台继续前台服务。

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

你应该在服务中重写onStartCommand方法：

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