ShakeListener

Terrormaster · by **Terrormaster** » Sat Feb 27, 2010 5:31 am

While working on my doodle app I thought it'd be cool to do an Etch-a-Sketch shake to erase kinda thing. I stumbled on a post here by snctln that demonstrates how to detect a shake using the accelerometer. The post was very informative and I was able to get it working in my app the way I wanted with little to no effort.

Being the type that likes to encapsulate things and make them reusable later down the line I thought wouldn't it be neat if this snippet say inside it's own listener that I could just implement in my activities? So I put this together and thought I'd share it with the folks here:

ShakeListener.java

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import java.util.List;
 
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
 
public class ShakeListener implements SensorEventListener{
    private static final String TAG = "ShakeListener";
 
        private OnShakeListener mOnShakeListener = null;  
    private SensorManager mSensorManager;
        private double mTotalForcePrev; // stores the previous total force value 
        private double mForceThreshHold = 1.5f;
 
        private List<Sensor> mSensors; 
        private Sensor mAccelerationSensor;
 
        public ShakeListener(SensorManager sm){
                mSensorManager = sm;
                
        mSensors = mSensorManager.getSensorList(Sensor.TYPE_ACCELEROMETER); 
        if(mSensors.size() > 0) { 
                mAccelerationSensor = mSensors.get(0);
                mSensorManager.registerListener(this, mAccelerationSensor, SensorManager.SENSOR_DELAY_GAME);
        }
        
        }
        
        public void setForceThreshHold(double threshhold){
                mForceThreshHold = threshhold;
        }
        public double getForceThreshHold(){
                return mForceThreshHold;
        }
        
        public void onAccuracyChanged(Sensor sensor, int accuracy) {}
        
    public void onSensorChanged(SensorEvent event) {    
          double totalForce = 0.0f; 
          totalForce += Math.pow(event.values[0]/SensorManager.GRAVITY_EARTH, 2.0); 
          totalForce += Math.pow(event.values[1]/SensorManager.GRAVITY_EARTH, 2.0); 
          totalForce += Math.pow(event.values[2]/SensorManager.GRAVITY_EARTH, 2.0); 
          totalForce = Math.sqrt(totalForce); 
           
          if((totalForce < mForceThreshHold) && (mTotalForcePrev > mForceThreshHold)) { 
                  OnShake(); // raise the onShake event.
          } 
           
          mTotalForcePrev = totalForce; 
    } 
    
    public void setOnShakeListener(OnShakeListener listener) {
        mOnShakeListener = listener;
    }  
 
    private void OnShake(){  
        if(mOnShakeListener!=null) {  
                mOnShakeListener.onShake();  
        }  
    }  
    
    public interface OnShakeListener {  
        public abstract void onShake();  
    }      
    
}       
 
Parsed in 0.038 seconds,  using GeSHi 1.0.8.4

And to implement it in an Activity just use the following:

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ShakeListener MyShake = new ShakeListener((SensorManager) getSystemService(SENSOR_SERVICE));
MyShake.setForceThreshHold(1.9);
MyShake.setOnShakeListener(new ShakeListener.OnShakeListener() {
        @Override
        public void onShake() {
                mPad.Clear();
        }
});
 
Parsed in 0.030 seconds,  using GeSHi 1.0.8.4

You can use MyShake.setForceThreshHold(1.9) to set the sensitivity of the shake.

Enjoy,
-TM

EDIT: Updated for API Level 3.

ShakeListener

ShakeListener

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