观察者模式

定义

 //定义动物接口
 public interface IAnimal
 {
     /// <summary>
     /// 动物名称
     /// </summary>
     public string _Name { get; set; }
     /// <summary>
     /// 动物行动
     /// </summary>
     void Action();
 }

 //定义猫(观察者)
 public class Cat : IAnimal
 {
     public string _Name { get; set; }

     public Cat(string Name)
     {
         _Name = Name;
     }
     public void Action()
     {
         Console.WriteLine($"小猫{_Name}开始跑");
     }
 }

 //定义狗(观察者)
 public class Dog : IAnimal
 {
     public string _Name { get; set; }

     public Dog(string Name) {
         _Name = Name;
     }

     public void Action()
     {
         Console.WriteLine($"小狗{_Name}开始叫");
     }
 }

 //定义主人(定义为单例)
 public class Owner
 {
     //事件
     public event Action? OwnerEvent;
     private static Owner? _ownerSlgtion;
     private static readonly object _lock = new object();

     private Owner()
     {
         OwnerEvent = new Action(() => { Console.WriteLine("事件初始化"); });
     }

     public static Owner GetOwner()
     {
         if (_ownerSlgtion == null)
         {
             lock (_lock)
             {
                 if (_ownerSlgtion == null)
                 {
                     _ownerSlgtion = new Owner();
                 }
             }
         }
         return _ownerSlgtion;
     }

     public void Action()
     {
         Console.WriteLine("主人回来了");
         OwnerEvent?.Invoke();//触发事件
     }

 }

 

 

 

调用

Console.WriteLine("观察者模式");
Cat cat1 = new Cat("Jim");
Dog dog1 = new Dog("Tom");
Owner owner1 = new Owner();

//事件不能在类外部进行初始化,而委托可以
//事件是一种特殊委托类型的实例
//事件更安全
//事件是为了当类内部变化时能通知类的外部

//订阅事件
owner1.OwnerEvent += cat1.Action;
owner1.OwnerEvent += dog1.Action;
owner1.Action();