Using the Accelerometer
The Accelerometer is part of the Sensors API, so to you will need to add a reference to Microsoft.Devices.Sensors. You will also want to add a using statement on the pages where you will be using the Accelerometer.
using Microsoft.Devices.Sensors;
Starting the Accelerometer and accessing its values is as simple as many of the other API calls you’ll make in developing a Windows Phone 7 application. In the code behind you declare a local variable of type Accelerometer and call its Start() method.
//declare a local variable
Accelerometer sensor;
private void Button_Click(object sender, RoutedEventArgs e)
{
sensor = new Accelerometer();
sensor.ReadingChanged += new EventHandler<AccelerometerReadingEventArgs>(sensor_ReadingChanged);
sensor.Start();
}
As with most calls to the device API’s, you will need to handle an event whenever the Accelerometer reading changes. As you can see in the code above, we are handling the ReadingChanged event which includes a parameter of class AccelerometerReadingEventArgs. AccelerometerReadingEventArgs contains a number of fields you will need to use in deciding which way the device has been moved, including the X,Y,X and a Timestamp value.
Whenever the readings from Accelerometer change, sensor_ReadingChanged is called, which invokes a background thread to handle the change of values.
void sensor_ReadingChanged(object sender, AccelerometerReadingEventArgs e)
{
//e contains X,Y,Z readings and a timestamp
Dispatcher.BeginInvoke(() => MyReadingChanged(e));
}
void MyReadingChanged(AccelerometerReadingEventArgs e)
{
TextBlockX.Text = e.X.ToString();
TextBlockY.Text = e.Y.ToString();
TextBlockZ.Text = e.Z.ToString();
TextBlockTimeStamp.Text = e.Timestamp.ToString();
}
Running this code will result in the values for X,Y,X and the Timestamp being displayed on the screen in their respective TextBlocks. The emulator can't move, so you will find the results somewhat boring. Running the app on a WP7 device however is a different story. Even when you place the device on a flat surface you will notice that the readings continually change, often many times per second. In a future post we will look at how you can smooth out these readings to obtain information about the general direction of movement.
