编辑代码

using System;

 //行为型模式——观察者模式

public interface ISubject{
    void AddObserver(IObserver ob);
    void RemoveObserver(IObserver ob);
    void Notify();
}

public interface IObserver{
    void Update(string message);
}

 //主题类
 public void Subject : ISubject
 {
     List<IObserver> observerList = new List<IObserver>;
     string message;
     void AddObserver(IObserver ob){
         observerList.Add(ob);
     }

     void RemoveObserver(IObserver ob){
         observerList.Remove(ob);
     }

     void Notify(){
        foreach(Observer obj in observerList){
           obj.Update(message);
         }
     }

     void Setmessage(string message){
         message = this.message;
         Notify();
     }
 }

 //观察者类
 public void Observer : IObserver
 {
     private string name;
     public Observer(string name){
         name = this.name;
     }
     void Update(string message){
         Console.WriteLine(name + " already receive "+ message);
     }
 }

public class HelloWorld
{
    public static void Main()
    {
      
    }
}