Android™ Application Development - Bahar Ali Khan

Chapter 10: Accessing Android Hardware
3. Create a new updateVelocity method that calculates the velocity change since the last update
based on the current acceleration.
private void updateVelocity() {
// Calculate how long this acceleration has been applied.
Date timeNow = new Date(System.currentTimeMillis());
long timeDelta = timeNow.getTime()-lastUpdate.getTime();
lastUpdate.setTime(timeNow.getTime());
}
// Calculate the change in velocity at the
// current acceleration since the last update.
float deltaVelocity = appliedAcceleration * (timeDelta/1000);
appliedAcceleration = currentAcceleration;
// Add the velocity change to the current velocity.
velocity += deltaVelocity;
// Convert from meters per second to miles per hour.
double mph = (Math.round(velocity / 1.6 * 3.6));
myTextView.setText(String.valueOf(mph) + “mph”);
4. Create a new SensorListener implementation that updates the current acceleration (and
derived velocity) whenever a change in acceleration is detected.
Because a speedometer will most likely be used while the device is mounted vertically, with the
screen face perpendicular to the ground, measure negative acceleration along the Z-axis.
private final SensorListener sensorListener = new SensorListener() {
double calibration - Double.NAN;
};
public void onSensorChanged(int sensor, float[] values) {
double x = values[SensorManager.DATA_X];
double y = values[SensorManager.DATA_Y];
double z = values[SensorManager.DATA_Z];
double a = -1*Math.sqrt(Math.pow(x, 2) +
Math.pow(y, 2) +
Math.pow(z, 2));
if (calibration == Double.NaN)
calibration = a;
else {
updateVelocity();
currentAcceleration = (float)a;
}
}
public void onAccuracyChanged(int sensor, int accuracy) {}
5. Update the onCreate method to register your new Listener for accelerometer updates using the
SensorManager. Take the opportunity to get a reference to the Text View.
@Override
public void onCreate(Bundle icicle) {
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