Implementing the Observer pattern

Now, let's implement the Observer pattern in a simple way that can be reused in various contexts:

1. We are going to start this code example by implementing the two elements of the pattern. Let's begin with the Subject class:

using UnityEngine;
using System.Collections;

namespace Chapter.Observer
{
    public abstract class Subject : MonoBehaviour
    {
        private readonly 
            ArrayList _observers = new ArrayList();

        public void Attach(Observer observer)
        {
            _observers.Add(observer);
        }

        public void Detach(Observer observer)
        {
            _observers.Remove(observer);
        }

        public void NotifyObservers()
        {
            foreach (Observer observer in _observers)
            {
                observer.Notify(this);
            }
        }
    }
}

The Subject abstract class has three methods. The first two, Attach() and Detach(), are responsible for adding or removing an observer object from...