Observable Pattern

Observable Pattern 

Gamma Categorization: Behavioral Design Pattern
Summary: Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically..

Sample Code

Problem: We want to trigger several events on the digital camera after a photo is taken.

Code

public class DigitalCamera 

{

    public event EventHandler PictureTaken;

    public void TakePicture()

    {

        System.Console.WriteLine("Taking picture.");

        PictureTaken?.Invoke(this, EventArgs.Empty);

    }

}

public class CameraSensorUtilities

{

    public void PictureTakenEventHandler(object sender, EventArgs args)

    {

        System.Console.WriteLine("Cleaning digital sensor.");

    }

}

public class SystemCounters

{

    public void PictureTakenEventHandler(object sender, EventArgs args)

    {

            System.Console.WriteLine("Updating camera counters.");

    }

}

Usage

var digitalCamera = new DigitalCamera();

var sensorUtils = new CameraSensorUtilities();

var counters = new SystemCounters();

digitalCamera.PictureTaken += sensorUtils.PictureTakenEventHandler;

digitalCamera.PictureTaken += counters.PictureTakenEventHandler;

digitalCamera.TakePicture();

Output

Taking picture.

Cleaning digital sensor.

Updating camera counters.