观察者模式（observer）之委托（delegate） c#简单例子

几个要点：模式使目标与观察都之间的依赖关系达到松耦合、通知会自动传播

例子：玩家击中敌人后发生一系列变化：发后爆炸、敌人少1个....

namespace adapterpattern
{
    public partial class observerDelegateForm : Form
    {
        public observerDelegateForm()
        {
            InitializeComponent();
            BaseData.EnemyNumber = 100;
        }

        private void btnDisplay_Click(object sender, EventArgs e)
        {

            ExplosionEvent explosionEvent = new ExplosionEvent();//观察员1
            Enemy enemy = new Enemy();//观察员2
            player p1 = new player1();
            p1.Update += new EventHandler(explosionEvent.ExplosionMax);//委托加入观察员1
            p1.Update += new EventHandler(enemy.Decrease);//委托中加入观察员2
            listBox1.Items.Add(p1.Display());
        }
    }
    public static class BaseData//数据中转站
    {
        public static string DisplayString { get; set; }
        public static int EnemyNumber { get; set; }
    }
    public delegate void EventHandler();//事件处理程序的委托
    public abstract class player
    {
        public event EventHandler Update;//声明一事件update
        protected virtual void Notify()//对加入事件执行通知
        {
            if (Update != null)
            {
               Update ();
            }
        }
        public abstract string Display();
    }
    public class player1 : player
    {

        public override string Display()
        {
             Notify ();//通知观察员;
            return BaseData.DisplayString + BaseData.EnemyNumber.ToString();
        }
    }
    public class ExplosionEvent  //观察员1
    {
        public void ExplosionMax()
        {
            BaseData.DisplayString = "显示大爆炸";
        }
        public void ExplosionMin()
        {
            BaseData.DisplayString = "显示小爆炸";
          }
        //.....
    }
    public class Enemy  //观察员2
    {
        public void Decrease()
        {
            BaseData.EnemyNumber -= 1;       //"敌人数减少1个";
        }
        //.....
    }
}