Skip to main content

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.

Comments

Post a Comment

Popular posts from this blog

XML Webservice (ASMX) - SOAP Request and Response Invocation logging

You are an integration developer. Eventualy you came into the state where there is nothing else you can debug, and you have to check which SOAP request it is built on the request, and which SOAP response you are getting from the server. C# XML Webservice (ASMX) - SOAP Request and Response Invocation logging In the legaccy .NET framework System.Web.Services , this means using soapExtensions to help you intersept the interaction with the webservice. This is done like so:  public class TraceExtension : SoapExtension     {         Stream oldStream;         Stream newStream;         string filename;         // Save the Stream representing the SOAP request or SOAP response into          // a local memory buffer.          public override Stream ChainStream(Stream stream)         {           ...
Post a Comment
Read more

Abstract Factory Pattern

Abstract Factory Pattern  Gamma Categorization: Creational Design Patten Summary: When the object construction is complicated, needing multiple arguments, we should create a separate function (Factory Method) or class (Factory), which is responsible for the creation of the all object. Problem examples Suport of multiple databases Multiple data sources: Serial port, ethernet port, device driver Diferent report types Solution Abstract class Generalized interface A Factory creates instances of the concrete classes Sample Code The abstract factory public   interface   IPhotoFactory {      IAnaloguePhoto   CreateAnaloguePhoto ();      IDigitalPhoto   CreateDigitalPhoto (); } The abstract products public   interface   IAnaloguePhoto {      string   GetName (); } public   interface   IDigitalPhoto {      ...
Post a Comment
Read more

SOLID (1/5) - Single Resposibility Principle

 SOLID (1/5) - Single Resposibility Principle The single-responsibility principle (SRP) is a computer-programming principle that states that every class in a computer program should have responsibility over a single part of that program's functionality, which it should encapsulate. All of that module, class or function's services should be narrowly aligned with that responsibility. In the following example we have a TodoList class which only handles it's own functionality logic, and then we have a Persistance class which handles the saving logic, hence keeping the concerns separeted. using   System ; using   System . Collections . Generic ; namespace   Journal {      public   class   TodoList     {          private   readonly   List < string >  _entries  =  new   List < string >();          private...
Post a Comment
Read more