程序代码：

class PubEventArgs : EventArgs
    {
        private readonly string m_magazineName;
        private readonly DateTime m_pubDate;

        public PubEventArgs(string magazineName, DateTime pubDate)
        {
            m_magazineName = magazineName;
            m_pubDate = pubDate;
        }
        public string MagazineName
        {
            get { return m_magazineName; }
        }
        public DateTime PubDate
        {
            get { return m_pubDate; }
        }
    }
    class Publisher  //出版者
    {
        public delegate void PubComputerEventHandler(object sender,PubEventArgs e);//声明事件所需的代理
        public delegate void PubLifeEventHandler(object sender, PubEventArgs e);

        public event PubComputerEventHandler PubComputer;//事件的声明
        public event PubLifeEventHandler PubLife;

        protected virtual void OnPubComputer(PubEventArgs e)
        {
            PubComputerEventHandler handler = PubComputer; // 疑问1
            if (handler != null)
            {
                handler(this,e);  // 疑问2
            }
        }
        protected virtual void OnPubLife(PubEventArgs e)
        {
            PubLifeEventHandler handler = PubLife;
            if (handler != null)
            {
                handler(this, e);
            }
        }
        public void issueComputer(string magazinName,DateTime pubDate)  //触发事件的方法
        {
            Console.WriteLine("发行"+magazinName);
            OnPubComputer(new PubEventArgs(magazinName, pubDate));
        }
        public void issueLife(string magazinName, DateTime pubDate)
        {
            Console.WriteLine("发行" + magazinName);
            OnPubLife(new PubEventArgs(magazinName, pubDate));
        }
    }

    class Subscriber  //订阅者
    {
        private string name;
        public Subscriber(string name)
        {
            this.name = name;
        }
        public void Receive(object sender,PubEventArgs e)  //在事件订阅者中定义事件处理程序
        {
            Console.WriteLine(e.PubDate+" "+name+"已经收到了"+e.MagazineName);
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Publisher Pub = new Publisher();
            Subscriber zs = new Subscriber("张三");
            Subscriber ls = new Subscriber("李四");
            Pub.PubComputer += new Publisher.PubComputerEventHandler(zs.Receive);  //向事件发行者订阅一个事件
            Pub.PubComputer += new Publisher.PubComputerEventHandler(ls.Receive);
            Pub.PubLife += new Publisher.PubLifeEventHandler(ls.Receive);
            Pub.issueComputer("电脑杂志",Convert.ToDateTime("2006-1-1"));
            Pub.issueLife("生活杂志",Convert.ToDateTime("2006-6-1"));
            Console.WriteLine();
            Console.WriteLine("一年后！");
            Pub.PubComputer -= new Publisher.PubComputerEventHandler(ls.Receive);
            Pub.issueComputer("电脑杂志", Convert.ToDateTime("2007-1-1"));
            Pub.issueLife("生活杂志", Convert.ToDateTime("2007-6-1"));

            Console.ReadKey();
        }
    }
疑问1：.PubComputerEventHandler handler = PubComputer;  
  handler是一个委托类型，PubComputer是声明的一个事件，这句话代表什么意思呢？
  2.handler(this,e);
  这句话就彻底不理解了。
  还望高手们不吝赐教，指点一下我们这些初学者。

if(PubComputer != null)
{
PubComputer(this, e);
}