Skip to main content

Command Pattern

Command Pattern 


Gamma Categorization: Behavioral Design Pattern
Summary: Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations.

Sample Code

Problem: We want to apply several commands on the digital camera.

Code

public interface ICommand
{
    void Execute();
}

public enum CameraCommands { ShutterSpeed, FocalDistance, ISO, Shoot }

public class ShutterSpeedCommand : ICommand
{
    private float shutterSpeed;

    public ShutterSpeedCommand(float shutterSpeed)
    {
        this.shutterSpeed = shutterSpeed;
    }

    public void Execute()
    {
        Console.WriteLine($"Setting shutter speed to {shutterSpeed} seconds.");
    }
}

public class FocalDistanceCommand : ICommand
{
    private int focalDistance;

    public FocalDistanceCommand(int focalDistance)
    {
        this.focalDistance = focalDistance;
    }

    public void Execute()
    {
        Console.WriteLine($"Setting focal distance to {focalDistance} mm.");
    }
}

public class ISOCommand : ICommand
{
    private int ISO;

    public ISOCommand(int ISO)
    {
        this.ISO = ISO;
    }

    public void Execute()
    {
        Console.WriteLine($"Setting ISO to {ISO}.");
    }
}

public class ShootCommand : ICommand
{
    public void Execute()
    {
        Console.WriteLine("Taking photo.");
    }
}

public class CameraInvoker
{
    public ICommand GetCommand(CameraCommands command, object parameter)
    {
        switch (command)
        {
            case CameraCommands.FocalDistance:
                return new FocalDistanceCommand((int)parameter);
            case CameraCommands.ShutterSpeed:
                return new ShutterSpeedCommand((float)parameter);
            case CameraCommands.ISO:
                return new ISOCommand((int)parameter);
            case CameraCommands.Shoot:
                return new ShootCommand();
            default:
                return null;
        }
    }
}

Usage

var cameraInvoker = new CameraInvoker();

var command = cameraInvoker.GetCommand(CameraCommands.FocalDistance, 28);
command.Execute();

command = cameraInvoker.GetCommand(CameraCommands.ShutterSpeed, 0.004f);
command.Execute();

command = cameraInvoker.GetCommand(CameraCommands.ISO, 100);
command.Execute();

command = cameraInvoker.GetCommand(CameraCommands.Shoot, null);
command.Execute();

Output

Setting focal distance to 28 mm.
Setting shutter speed to 0.004 seconds.
Setting ISO to 100.
Taking photo.

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