Android Open Source - crystalball Shake Detector

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License

The source code is released under:

This is free and unencumbered software released into the public domain. Anyone is free to copy, modify, publish, use, compile, sell, or distribute this software, either in source code form or as a co...

Java Source Code

package com.es0329.crystalball;
// www. ja  va2 s  .  com
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;
  }

  /*
   * Definition for OnShakeListener definition. I would normally put this into
   * it's own .java file, but I included it here for quick reference and to
   * make it easier to include this file in our project.
   */
  public interface OnShakeListener {
    public void onShake();
  }
}

Java Source Code List

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