How to refresh app upon shaking the device?

Question

I need to add a shake feature that will refresh my Android application.

All I find of documentation involves implementing the SensorListener, but Eclips

Answer 1

I am developing a motion-detection and shake-detection app for my university project.

Besides the original target of the application, I am splitting the library part (responsible for motion and shake detection) from the app. The code is free, available on SourceForge with the project name "BenderCatch". Documentation I am producing will be ready around mid-september. http://sf.net/projects/bendercatch

It uses a more precise way to detect shake: watches BOTH the difference of force between SensorEvents AND the oscillations present in X and Y axis when you perform a shake. It can even make a sound (or vibrate) on each oscillation of the shake.

Feel free to ask me more by e-mail at raffaele [at] terzigno [dot] com

Answer 2

Here's yet another implementation that builds on some of the tips in here as well as the code from the Android developer site.

MainActivity.java

public class MainActivity extends Activity {

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

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // ShakeDetector initialization
        mSensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
        mAccelerometer = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
        mShakeDetector = new ShakeDetector(new OnShakeListener() {
            @Override
            public void onShake() {
                // Do stuff!
            }
        });
    }

    @Override
    protected void onResume() {
        super.onResume();
        mSensorManager.registerListener(mShakeDetector, mAccelerometer, SensorManager.SENSOR_DELAY_UI);
    }

    @Override
    protected void onPause() {
        mSensorManager.unregisterListener(mShakeDetector);
        super.onPause();
    }   
}

ShakeDetector.java

package com.example.test;

import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;

public class ShakeDetector implements SensorEventListener {

    // Minimum acceleration needed to count as a shake movement
    private static final int MIN_SHAKE_ACCELERATION = 5;

    // Minimum number of movements to register a shake
    private static final int MIN_MOVEMENTS = 2;

    // Maximum time (in milliseconds) for the whole shake to occur
    private static final int MAX_SHAKE_DURATION = 500;

    // Arrays to store gravity and linear acceleration values
    private float[] mGravity = { 0.0f, 0.0f, 0.0f };
    private float[] mLinearAcceleration = { 0.0f, 0.0f, 0.0f };

    // Indexes for x, y, and z values
    private static final int X = 0;
    private static final int Y = 1;
    private static final int Z = 2;

    // OnShakeListener that will be notified when the shake is detected
    private OnShakeListener mShakeListener;

    // Start time for the shake detection
    long startTime = 0;

    // Counter for shake movements
    int moveCount = 0;

    // Constructor that sets the shake listener
    public ShakeDetector(OnShakeListener shakeListener) {
        mShakeListener = shakeListener;
    }

    @Override
    public void onSensorChanged(SensorEvent event) {
        // This method will be called when the accelerometer detects a change.

        // Call a helper method that wraps code from the Android developer site
        setCurrentAcceleration(event);

        // Get the max linear acceleration in any direction
        float maxLinearAcceleration = getMaxCurrentLinearAcceleration();

        // Check if the acceleration is greater than our minimum threshold
        if (maxLinearAcceleration > MIN_SHAKE_ACCELERATION) {
            long now = System.currentTimeMillis();

            // Set the startTime if it was reset to zero
            if (startTime == 0) {
                startTime = now;
            }

            long elapsedTime = now - startTime;

            // Check if we're still in the shake window we defined
            if (elapsedTime > MAX_SHAKE_DURATION) {
                // Too much time has passed. Start over!
                resetShakeDetection();
            }
            else {
                // Keep track of all the movements
                moveCount++;

                // Check if enough movements have been made to qualify as a shake
                if (moveCount > MIN_MOVEMENTS) {
                    // It's a shake! Notify the listener.
                    mShakeListener.onShake();

                    // Reset for the next one!
                    resetShakeDetection();
                }
            }
        }
    }

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

    private void setCurrentAcceleration(SensorEvent event) {
        /*
         *  BEGIN SECTION from Android developer site. This code accounts for 
         *  gravity using a high-pass filter
         */

        // alpha is calculated as t / (t + dT)
        // with t, the low-pass filter's time-constant
        // and dT, the event delivery rate

        final float alpha = 0.8f;

        // Gravity components of x, y, and z acceleration
        mGravity[X] = alpha * mGravity[X] + (1 - alpha) * event.values[X];
        mGravity[Y] = alpha * mGravity[Y] + (1 - alpha) * event.values[Y];
        mGravity[Z] = alpha * mGravity[Z] + (1 - alpha) * event.values[Z];

        // Linear acceleration along the x, y, and z axes (gravity effects removed)
        mLinearAcceleration[X] = event.values[X] - mGravity[X];
        mLinearAcceleration[Y] = event.values[Y] - mGravity[Y];
        mLinearAcceleration[Z] = event.values[Z] - mGravity[Z];

        /*
         *  END SECTION from Android developer site
         */
    }

    private float getMaxCurrentLinearAcceleration() {
        // Start by setting the value to the x value
        float maxLinearAcceleration = mLinearAcceleration[X];

        // Check if the y value is greater
        if (mLinearAcceleration[Y] > maxLinearAcceleration) {
            maxLinearAcceleration = mLinearAcceleration[Y];
        }

        // Check if the z value is greater
        if (mLinearAcceleration[Z] > maxLinearAcceleration) {
            maxLinearAcceleration = mLinearAcceleration[Z];
        }

        // Return the greatest value
        return maxLinearAcceleration;
    }

    private void resetShakeDetection() {
        startTime = 0;
        moveCount = 0;
    }

    // (I'd normally put this definition in it's own .java file)
    public interface OnShakeListener {
        public void onShake();
    }
}

Answer 3

I have tried several implementations, but would like to share my own. It uses G-force as unit for the threshold calculation. It makes it a bit easier to understand what is going on, and also with setting a good threshold.

It simply registers a increase in G force and triggers the listener if it exceeds the threshold. It doesn't use any direction thresholds, cause you don't really need that if you just want to register a good shake.

Of-course you need the standard registering and UN-registering of this listener in the Activity.

Also, to check what threshold you need, I recommend the following app (I am not in any way connected to that app)

    public class UmitoShakeEventListener implements SensorEventListener {

    /**
     * The gforce that is necessary to register as shake. (Must include 1G
     * gravity)
     */
    private final float shakeThresholdInGForce = 2.25F;

    private final float gravityEarth = SensorManager.GRAVITY_EARTH;

    private OnShakeListener listener;

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

    public interface OnShakeListener {
        public void onShake();
    }

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

    }

    @Override
    public void onSensorChanged(SensorEvent event) {

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

            float gX = x / gravityEarth;
            float gY = y / gravityEarth;
            float gZ = z / gravityEarth;

            //G-Force will be 1 when there is no movement. (gravity)
            float gForce = FloatMath.sqrt(gX * gX + gY * gY + gZ * gZ); 



            if (gForce > shakeThresholdInGForce) {
                listener.onShake();

            }
        }

    }

}

Answer 4

You should subscribe as a SensorEventListener, and get the accelerometer data. Once you have it, you should monitor for sudden change in direction (sign) of acceleration on a certain axis. It would be a good indication for the 'shake' movement of device.