C#事件的用法

    //事件提供者，提供事件为其成员NUM的值改变。事件为静态事件NumChange
    class EventExp
    {
        static private int num;
        //public EventExp exp;
        public delegate void NumChangeEventHandler(object sender, NumChangeEventArgs e,int i);
        static public event NumChangeEventHandler NumChange;
        static public int Num{get{ return EventExp.num; }set { EventExp.num = value; EventExp.NumberChanged(); } }
        static public void NumberChanged()
        {
            if (EventExp.NumChange != null)
            {
                EventExp.NumChange(null, new NumChangeEventArgs(), EventExp.num);//此处本来是想传入EventExp类本身，但是不知道怎么传。
            }
        }
    }
    //定义的一个事件参数类型，继承自EventArgs
    class NumChangeEventArgs : EventArgs
    {
        public DateTime dateTime { get { return DateTime.Now; } }
    }
    //事件的观察者，观察事件提供者的事件有无发生

    class exp
    {
        
        public void hello(object sender, NumChangeEventArgs e, int i)
        {
            Console.WriteLine("我观察到EventExp{0}的Num值发生了变化，变化的时间是{1},改变后的值是：{2}",sender,e.dateTime,i);
        }
    }

            exp e = new exp();
            EventExp.NumChange += e.hello;
            EventExp.Num = 10;
            Console.ReadLine();