Question

I got this code from the site http://www.clingmarks.com/?p=25, and i would like some help with it!

This code registers shaking of the phone. It only allows updates every 100 millisecs and the value of the shaking has to be over 800, SHAKE_THRESHOLD.

What I have problem with is that if the phone detects a shake, (then variable i++) I would like not to be able to reach that block of code, before a certain time has passed.

Could someone help me?

public class ShakeActivity extends Activity implements SensorListener {
    // For shake motion detection.
    private SensorManager sensorMgr;
    private long lastUpdate = -1;
    private float x, y, z;
    int i = 0;
    private float last_x, last_y, last_z;
    private static final int SHAKE_THRESHOLD = 800;

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ...... // other initializations
            // start motion detection
            sensorMgr = (SensorManager) getSystemService(SENSOR_SERVICE);
        boolean accelSupported = sensorMgr.registerListener(this,
                SensorManager.SENSOR_ACCELEROMETER,
                SensorManager.SENSOR_DELAY_GAME);

        if (!accelSupported) {
            // on accelerometer on this device
            sensorMgr.unregisterListener(this,
                    SensorManager.SENSOR_ACCELEROMETER);
        }
    }

    protected void onPause() {
        if (sensorMgr != null) {
            sensorMgr.unregisterListener(this,
                    SensorManager.SENSOR_ACCELEROMETER);
            sensorMgr = null;
        }
        super.onPause();
    }

    public void onAccuracyChanged(int arg0, int arg1) {
        // TODO Auto-generated method stub
    }

    public void onSensorChanged(int sensor, float[] values) {
        if (sensor == SensorManager.SENSOR_ACCELEROMETER) {
            long curTime = System.currentTimeMillis();
            // only allow one update every 100ms.
            if ((curTime - lastUpdate) > 100) {
                long diffTime = (curTime - lastUpdate);
                lastUpdate = curTime;

                x = values[SensorManager.DATA_X];
                y = values[SensorManager.DATA_Y];
                z = values[SensorManager.DATA_Z];

                float speed = Math.abs(x+y+z - last_x - last_y - last_z)
                    / diffTime * 10000;
                if (speed > SHAKE_THRESHOLD) {
                    // yes, this is a shake action! Do something about it!
                    i++;
                }
                last_x = x;
                last_y = y;
                last_z = z;
            }
        }
    }
}

Answer 1

The behavior you want is known as a “holdoff”. You want to set a certain variable on your Activity object:

    private long last_shake_time = 0;

and then check and update that in the code that registers a shake:

            if (speed > SHAKE_THRESHOLD) {
                // yes, this is a shake action!
                long shake_time = System.currentTimeMillis();
                if (shake_time - last_shake_time >= SHAKE_HOLDOFF_MS) {
                    i++;
                    last_shake_time = shake_time;
                }
            }

With SHAKE_HOLDOFF_MS defined just like the SHAKE_THRESHOLD constant:

    private static final long SHAKE_HOLDOFF_MS = 5000;