Mediator

Defines an object that encapsulates how a set of objects interact, reducing coupling between them.

Context

You have 7 controls on a form that affect each other. Each one knows several others — N×N references.

Problem

M:N coupling.
Difficult to add/remove components.

Solution

Components communicate only with a central Mediator. This changes communication from N×N to N×1.

#Example in C#

public interface IDialogMediator { void Notify(object sender, string evt); }

public class LoginDialog : IDialogMediator
{
    public TextBox User = new(); public TextBox Pass = new(); public Button Login = new();

    public LoginDialog()
    {
        User.Mediator = Pass.Mediator = Login.Mediator = this;
    }

    public void Notify(object sender, string evt)
    {
        if (sender is TextBox && evt == "changed")
            Login.Enabled = User.Text.Length > 0 && Pass.Text.Length >= 8;
    }
}

When NOT to use it

If the mediator becomes a God Object containing all the module's logic.

Tradeoffs

Pro	Con
Reduces coupling between components	Centralizes logic in a single point
Fits with MediatR / event bus	Risk of god object

#behavioral #gof