Alright, when you look at what apps are popular, you’ll see a lot of apps that interact with the accelerometer in a way like: Shake your phone baby!
Yes we have the accelerometer on the Windows Phone 7 as well, how to use it? That’s simple.
1: Reference the Microsoft.Devices.Sensors assembly.
2: Create an instance of the Accelerometer.
private readonly Accelerometer _sensor = new Accelerometer();
3: Start listening to the ReadingChanged
_sensor.ReadingChanged += ReadingChanged;
private void ReadingChanged(object sender, AccelerometerReadingEventArgs e)
{
}The structure of the AccelerometerReadingEventArgs looks like this.
public class AccelerometerReadingEventArgs : EventArgs
{
public double X { get; }
public double Y { get; }
public double Z { get; }
public DateTimeOffset Timestamp { get; }
}Pretty simple, X, Y and Z coordinates, how to read them?
Shake it
That’s about it for the basics. You can do a lot of things with the accelerometer. I want to know when the device is shaken. I started with a bit of google, and found: Shake Detection by Mark Arteaga. Nice article with a good explanation of the code. Though, he didn’t have a chance to test the code, and it was also based on a pre-release version of the Developer Tools. So after some adjustments I came with the following code that both compiles in the final Windows Phone 7 Developers Tools and also runs on the LG Prototype.
public class AccelerometerSensorWithShakeDetection : IDisposable
{
private const double ShakeThreshold = 0.7;
private readonly Accelerometer _sensor = new Accelerometer();
private AccelerometerReadingEventArgs _lastReading;
private int _shakeCount;
private bool _shaking;
public AccelerometerSensorWithShakeDetection()
{
var sensor = new Accelerometer();
if (sensor.State == SensorState.NotSupported)
throw new NotSupportedException("Accelerometer not supported on this device");
_sensor = sensor;
}
public SensorState State
{
get { return _sensor.State; }
}
#region IDisposable Members
public void Dispose()
{
if (_sensor != null)
_sensor.Dispose();
}
#endregion
private event EventHandler ShakeDetectedHandler;
public event EventHandler ShakeDetected
{
add
{
ShakeDetectedHandler += value;
}
remove
{
ShakeDetectedHandler -= value;
_sensor.ReadingChanged -= ReadingChanged;
}
}
public void Start()
{
if (_sensor != null)
_sensor.Start();
}
public void Stop()
{
if (_sensor != null)
_sensor.Stop();
}
private void ReadingChanged(object sender, AccelerometerReadingEventArgs e)
{
//Code for checking shake detection
if (_sensor.State == SensorState.Ready)
{
AccelerometerReadingEventArgs reading = e;
try
{
if (_lastReading != null)
{
if (!_shaking && CheckForShake(_lastReading, reading, ShakeThreshold) && _shakeCount >= 1)
{
//We are shaking
_shaking = true;
_shakeCount = 0;
OnShakeDetected();
}
else if (CheckForShake(_lastReading, reading, ShakeThreshold))
{
_shakeCount++;
}
else if (!CheckForShake(_lastReading, reading, 0.2))
{
_shakeCount = 0;
_shaking = false;
}
}
_lastReading = reading;
}
catch
{
/* ignore errors */
}
}
}
private void OnShakeDetected()
{
if (ShakeDetectedHandler != null)
ShakeDetectedHandler(this, EventArgs.Empty);
}
private static bool CheckForShake(AccelerometerReadingEventArgs last, AccelerometerReadingEventArgs current,
double threshold)
{
double deltaX = Math.Abs((last.X - current.X));
double deltaY = Math.Abs((last.Y - current.Y));
double deltaZ = Math.Abs((last.Z - current.Z));
return (deltaX > threshold && deltaY > threshold) ||
(deltaX > threshold && deltaZ > threshold) ||
(deltaY > threshold && deltaZ > threshold);
}
}
And of course you want to use it in your app, which can be done like this.
_shakeSensor = new AccelerometerSensorWithShakeDetection();
Loaded += (sender, args) =>
{
_shakeSensor.ShakeDetected += ShakeDetected;
_shakeSensor.Start();
};
Unloaded += (sender, args) =>
{
_shakeSensor.ShakeDetected -= ShakeDetected;
_shakeSensor.Stop();
};
I'm seeking your permission to reuse this code in some examples for WP7 Hands-On-Labs. Can you contact me please?
Thank you.
add
{
ShakeDetectedHandler += value;
}
Should actually read:
add
{
ShakeDetectedHandler += value;
_sensor.ReadingChanged += ReadingChanged;
}
And secondly you don't mention that in your code you need a ShakeDetected handler, i.e.:
private void ShakeDetected(object sender, EventArgs e)
{
}
Great article, though - saved me a ton of work!