Wednesday, December 31, 2014

Command design pattern. Simple version.

Hello
We have Light devices, which can beam or not.
We do not want control directly Light source, because we want learn Command Design Pattern :-)
Of course, the reasons is others. For example, we want to be less sensitive to changes.

In implementation of Command Design Patter in our example we have 3 players:

  • Device: is a Light which can be "ON" or "OFF" state.
  • Command turn "ON" the lights: is Light "ON" command. Is a class, which wraps above Light. Heart of this class - turn "ON" the Light, which encapsulated in single function "Execute". 
  • Remote: some class which got command and call it "Execute". When user call "Click Remote" of this class, its method call "Execute" of command
Illustration:




Code behind it:
public interface ICommand
{
    void Execute();
}

public class Light
{
    public void On()
    {
        Console.WriteLine("Light is ON");
    }

    public void Off()
    {
        Console.WriteLine("Light is OFF");
    }
}

public class LightOnCommand : ICommand
{
    private Light _light;

    public LightOnCommand(Light light)
    {
        _light = light;
    }

    public void Execute()
    {
        _light.On();
    }
}

public class SimpleRemoteControl
{
    ICommand _command;

    public void SetCommand(ICommand command)
    {
        _command = command;
    }

    public void ClickButton()
    {
        _command.Execute();
    }
}

Tester:
Light light = new Light();
ICommand lightOnCmd = new LightOnCommand(light);

SimpleRemoteControl remote = new SimpleRemoteControl();
remote.SetCommand(lightOnCmd);
remote.ClickButton();

Result:

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