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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.

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