.NET 观察者模式

一、原始模式
1. 定义一个主题接口类 【ISubject】，所有的被观察都要实现该接口

public interface ISubject{
    void RegisterObserver(IObserver o);  //注册观察者
    void RemoveObserver(IObserver o);   //注销观察者
    void notifyObservers();    // 数据发生变化时，通知观察者
}

1. 定义一个观察者接口 【IObserver】，所有的观察者都需要实现该接口的 Update 方法 ```csharp interface IObserver { void Update(float temp,float humidity,float pressure); }

interface IDisplayElement { void display(); }

3. 主题接口实现类
```csharp
public class WeatherData:ISubject
{
    private float tempeature; // 温度
    private float humidity;// 湿度
    private float pressure; // 压力
    private List<IObserver> observers;// 观察者列表，存储所有的观察者
    public WeatherData(){
      observers=new List<IObserver>();
    }

    #region 继承 ISubject 接口
    public void RegisterObserver(IObserver o)
    {
      observers.Add(o);
    }

    public void RemoveObserver(IObserver o)
    {
       int i=observers.IndexOf(o);
       observers.RemoveAt(i);
    }

    public void notifyObservers()
    {
      foreach(IObserver o in observers)
      {
         o.Update(temperature,humidity,pressure);
      }
    }
    #endrgion

    // 数据内容发生变化时，通知观察者发生改变
    public void SetMeasurements(string temperature,string humidity,string pressure)
    {
        float temp;
        float.TryParse(temperature,out temp);
        this.tempreature=temp;
        float.TryParse(humidity,out temp);
        this.humidity=temp;
        float.TryParse(humidity,out temp);
        this.humidity=temp;
        this.pressure=temp;
        measurementsChanged();
    }

    public void measurementsChanged()
    {
        notifyObservers();
    }





}

1. 具体观察者

   public class CurrentObserver:IObserver,IDisplayElement
   {
    private float temperature;
    private float humidity;
    private void Update(float temperature,float humidity,float pressure)
    {
       this.tempreature=temperature;
       this.humidity=humidity;
       display();
    }
   
    public void didplay()
    {
        Console.WriteLine("现状："+temperature+"F度 和"+humidity+"% 湿度");
    }
   }
   

2. 客户端实现 ```csharp static void Main(string[] args) { int n=Convert.ToInt32(Console.ReadLine()); WeatherData data=new WeatehrData(); data.RegisterObserver(new CurrentObserver());

   for(int i=0;i<n;i++) {

    string str=Console.ReadLine();
    string[] arr=str.Split(',');
    data.setMeasurements(arr[0],arr[1],arr[2]);
   

   }

}

二、委托事件模式<br /> 1.  主题类
```csharp

// 委托充当观察者接口类
pubic deletegate void NotifyEventHandler(object sender); 
public class WeatherData
{
    public Event NotifyEventHandler NotifyEvent;

    public  float Temperature {get;set;}   // 温度
    public  float Humidity {get;set;}     // 湿度
    public  float Pressure {get;set;}     // 压力

    public WeatherData(temperature,humidity,presure)
    {
        this.Temperature=temperature;
        this.Humidity=humidity;
        this.Pressure=presue;

    }

     public void RegisterObserver(NotifyEventHandler obj)
     {
         NotifyEventHandler+=obj;
     }

     public void RemoveObserver(NotifyEventHandler obj)
     {
         NotifyEventHandler-=obj;
     }

     public void Update()
     {
         if(NotifyEvent!=null)
         {
             NotifyEvent(this);
         }
     }

}

1. 观察者类

   public class Observer
   {
    public Update(object obj)
    {
        var  ob=obj as WeatherData;
        if(ob!=null)
        {
          Console.writeLine("temp"+ob.Temperature);
        }
   
    }
   }
   

2. 客户端实现

   class Program{
    static void Main(String[] args)
    {
        WeatherData weather=new WeatherData(1,2,3);
        Observer o1=new Observer();
        weather.RegisterObserver(new NotifyEventHandler(o1.Update));
        weather.Update();
        Console.ReadyKey();
     }
   }
   

三、IObservable和IObserver