c#之事件用法

//事件发布类
        public class PublishEvent
        {
            public delegate string Display(string str);
            public event Display DisplayEvent;

            //客户端代码通过调用这个方法触发事件
            public void Shows(string str)
            {
                if (DisplayEvent != null)
                {
                    DisplayEvent(str);
                }
            }

        }

        //事件侦听类，这个类订阅事件
        public class Listen1
        {
            public string MakeAlert(string str)
            {
                Console.WriteLine(str + "Listen1");
                return str + "Listen1";
            }
        }
        public class Listen2
        {
            public string ShowMsg(string str)
            {
                Console.WriteLine(str + "Listen2");
                return str + "Listen2";
            }
        }

class Program
        {
            static void Main()
            {
                PublishEvent pe = new PublishEvent();
                Listen1 l1 =  new Listen1();
                Listen2 l2 = new Listen2();

                //变量l1和l2订阅了事件
                pe.DisplayEvent += l1.MakeAlert;
                pe.DisplayEvent += l2.ShowMsg;

                //触发事件
                pe.Shows("事件");

                Console.ReadKey();

            }
        }