命令模式混乱

Question

Command Pattern Says:

Command Pattern allows you to decouple the requester of an action from the object that actually performs the action.

Command decouples the object that invokes the operation from the one that knows how to perform it .

But in all code examples which I found there is coupling between Client(Requester,Inovker,RemoteControl,Waitress,Sender) and the actual object (Reciver,TV,Garage,Coffe)

If you this question in the below Command pattern

Answer: Says : Your remote doesn't know that the TV exists , or anything about it, its just calling an interface/method on your Command object.

But I see Remote Class is aware of TV class and it (remote) is creating object of TV class. Hence there is association there by a relation ie A coupling already exists there.

Can you please help me to understand what I am missing. Do I misunderstand what is meant by decoupling or some thing other ?

I am really confusing with definition.

Answer 1

I think instead of TV it should be an interface like ITV

public class TVOffCommand : Command    
{
    ITV tv;

    public TVOffCommand (ITV aTV)
    {
        this.tv= aTv;
    }

    #region Command Members

    public object Execute()
    {
        return tv.Off();
    }

    #endregion
}

and your remote should invoke something like below:

ITV tv = new TV()

remote = new Remote() //your client

command = new TVOffCommand(tv);

remote.command(command);

Have a look at link this provides the concept http://www.codeproject.com/Articles/165368/WPF-MVVM-Quick-Start-Tutorial

Answer 2

I don't think that it make sense to wrap the example regarding TV and remote control into command design pattern. You just have TV and remote control. Even if you would add interfaces, it does not make sense as there is small (or no) level of abstraction.

The last sentence is the whole point of command design pattern. There must be some abstraction and unawarness. Typically you have some system which accept executable command (using defined IF = contract) which does "something".

It's up to your implementations of this IF , typically there is more implementations than one. What was my last use?

We have scheduling system using Quartz framework. We have wrapped it into some kind of our service. This service accepts our IF having perform method in a certain time - using quartz.

We have two types of executable tasks - one was executed immediately and second was was rescheduled with additional time - because of other reasons out of scope of this question.

Both types of tasks were executed despite what they do , despite they real executable code. And the wrapping service has no knowledge what's going on there and both types of tasks have no knowledge regarding scheduling system.