Shaker.java

package apt.tutorial;

import android.content.Context;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.SystemClock;
import java.util.ArrayList;
import java.util.List;

public class Shaker {
	private SensorManager mgr=null;
	private long lastShakeTimestamp=0;
	private double threshold=1.0d;
	private long gap=0;
	private Shaker.Callback cb=null;
	
	public Shaker(Context ctxt, double threshold, long gap,
									Shaker.Callback cb) {
		this.threshold=threshold*threshold;
		this.threshold=this.threshold
										*SensorManager.GRAVITY_EARTH
										*SensorManager.GRAVITY_EARTH;
		this.gap=gap;
		this.cb=cb;
		
		mgr=(SensorManager)ctxt.getSystemService(Context.SENSOR_SERVICE);
		mgr.registerListener(listener,
													mgr.getDefaultSensor(Sensor.TYPE_ACCELEROMETER),
													SensorManager.SENSOR_DELAY_UI);
	}
	
	public void close() {
		mgr.unregisterListener(listener);
	}
	
	private void isShaking() {
		long now=SystemClock.uptimeMillis();
		
		if (lastShakeTimestamp==0) {
			lastShakeTimestamp=now;
			
			if (cb!=null) {
				cb.shakingStarted();
			}
		}
		else {
			lastShakeTimestamp=now;
		}
	}
	
	private void isNotShaking() {
		long now=SystemClock.uptimeMillis();
		
		if (lastShakeTimestamp>0) {
			if (now-lastShakeTimestamp>gap) {
				lastShakeTimestamp=0;
				
				if (cb!=null) {
					cb.shakingStopped();
				}
			}
		}
	}
	
	public interface Callback {
		void shakingStarted();
		void shakingStopped();
	}
	
	private SensorEventListener listener=new SensorEventListener() {
		public void onSensorChanged(SensorEvent e) {
			if (e.sensor.getType()==Sensor.TYPE_ACCELEROMETER) {
				double netForce=e.values[0]*e.values[0];
				
				netForce+=e.values[1]*e.values[1];
				netForce+=e.values[2]*e.values[2];
				
				if (threshold<netForce) {
					isShaking();
				}
				else {
					isNotShaking();
				}
			}
		}
		
		public void onAccuracyChanged(Sensor sensor, int accuracy) {
			// unused
		}
	};
}