IObserver<T> 接口

定义

提供用于接收基于推送的通知的机制。Provides a mechanism for receiving push-based notifications.

generic <typename T>
public interface class IObserver
public interface IObserver<in T>
type IObserver<'T> = interface
Public Interface IObserver(Of In T)

类型参数

T

提供通知信息的对象。The object that provides notification information.

这是逆变类型参数。 即,可以使用指定的类型,也可以使用派生程度较低的任何类型。 有关协变和逆变的详细信息,请参阅泛型中的协变和逆变
派生

示例

下面的示例演示观察者设计模式。The following example illustrates the observer design pattern. 它定义 Location 包含纬度和经度信息的类。It defines a Location class that contains latitude and longitude information.

public struct Location
{
   double lat, lon;

   public Location(double latitude, double longitude)
   {
      this.lat = latitude;
      this.lon = longitude;
   }

   public double Latitude
   { get { return this.lat; } }

   public double Longitude
   { get { return this.lon; } }
}
Public Structure Location
   Dim lat, lon As Double

   Public Sub New(ByVal latitude As Double, ByVal longitude As Double)
      Me.lat = latitude
      Me.lon = longitude
   End Sub

   Public ReadOnly Property Latitude As Double
      Get
         Return Me.lat
      End Get
   End Property

   Public ReadOnly Property Longitude As Double
      Get
         Return Me.lon
      End Get
   End Property
End Structure

LocationReporter类提供 IObserver<T> 实现。The LocationReporter class provides the IObserver<T> implementation. 它显示有关当前控制台位置的信息。It displays information about the current location to the console. 其构造函数包含一个 name 参数,该参数允许 LocationReporter 实例在其字符串输出中标识自身。Its constructor includes a name parameter, which allows the LocationReporter instance to identify itself in its string output. 它还包括一个 Subscribe 方法,该方法将调用提供程序的 Subscribe 方法。It also includes a Subscribe method, which wraps a call to the provider's Subscribe method. 这使方法可以将返回的 IDisposable 引用分配给私有变量。This enables the method to assign the returned IDisposable reference to a private variable. LocationReporter类还包含 Unsubscribe 方法,该方法调用 IDisposable.Dispose 方法返回的对象的方法 IObservable<T>.SubscribeThe LocationReporter class also includes an Unsubscribe method, which calls the IDisposable.Dispose method of the object returned by the IObservable<T>.Subscribe method. 下面的代码定义 LocationReporter 类。The following code defines the LocationReporter class.

using System;

public class LocationReporter : IObserver<Location>
{
   private IDisposable unsubscriber;
   private string instName;

   public LocationReporter(string name)
   {
      this.instName = name;
   }

   public string Name
   {  get{ return this.instName; } }

   public virtual void Subscribe(IObservable<Location> provider)
   {
      if (provider != null)
         unsubscriber = provider.Subscribe(this);
   }

   public virtual void OnCompleted()
   {
      Console.WriteLine("The Location Tracker has completed transmitting data to {0}.", this.Name);
      this.Unsubscribe();
   }

   public virtual void OnError(Exception e)
   {
      Console.WriteLine("{0}: The location cannot be determined.", this.Name);
   }

   public virtual void OnNext(Location value)
   {
      Console.WriteLine("{2}: The current location is {0}, {1}", value.Latitude, value.Longitude, this.Name);
   }

   public virtual void Unsubscribe()
   {
      unsubscriber.Dispose();
   }
}
Public Class LocationReporter : Implements IObserver(Of Location)
   Dim unsubscriber As IDisposable
   Dim instName As String

   Public Sub New(ByVal name As String)
      Me.instName = name
   End Sub

   Public ReadOnly Property Name As String
      Get
         Return instName
      End Get
   End Property

   Public Overridable Sub Subscribe(ByVal provider As IObservable(Of Location))
      If provider Is Nothing Then Exit Sub
      unsubscriber = provider.Subscribe(Me)
   End Sub

   Public Overridable Sub OnCompleted() Implements System.IObserver(Of Location).OnCompleted
      Console.WriteLine("The Location Tracker has completed transmitting data to {0}.", Me.Name)
      Me.Unsubscribe()
   End Sub

   Public Overridable Sub OnError(ByVal e As System.Exception) Implements System.IObserver(Of Location).OnError
      Console.WriteLine("{0}: The location cannot be determined.", Me.Name)
   End Sub

   Public Overridable Sub OnNext(ByVal value As Location) Implements System.IObserver(Of Location).OnNext
      Console.WriteLine("{2}: The current location is {0}, {1}", value.Latitude, value.Longitude, Me.Name)
   End Sub

   Public Overridable Sub Unsubscribe()
      unsubscriber.Dispose()
   End Sub
End Class

LocationTracker类提供 IObservable<T> 实现。The LocationTracker class provides the IObservable<T> implementation. TrackLocation向其方法传递 Location 包含纬度和经度数据的可以为 null 的对象。Its TrackLocation method is passed a nullable Location object that contains the latitude and longitude data. 如果 Location 值不为 null ,则 TrackLocation 方法调用 OnNext 每个观察程序的方法。If the Location value is not null, the TrackLocation method calls the OnNext method of each observer.

public class LocationTracker : IObservable<Location>
{
   public LocationTracker()
   {
      observers = new List<IObserver<Location>>();
   }

   private List<IObserver<Location>> observers;

   public IDisposable Subscribe(IObserver<Location> observer)
   {
      if (! observers.Contains(observer))
         observers.Add(observer);
      return new Unsubscriber(observers, observer);
   }

   private class Unsubscriber : IDisposable
   {
      private List<IObserver<Location>>_observers;
      private IObserver<Location> _observer;

      public Unsubscriber(List<IObserver<Location>> observers, IObserver<Location> observer)
      {
         this._observers = observers;
         this._observer = observer;
      }

      public void Dispose()
      {
         if (_observer != null && _observers.Contains(_observer))
            _observers.Remove(_observer);
      }
   }

   public void TrackLocation(Nullable<Location> loc)
   {
      foreach (var observer in observers) {
         if (! loc.HasValue)
            observer.OnError(new LocationUnknownException());
         else
            observer.OnNext(loc.Value);
      }
   }

   public void EndTransmission()
   {
      foreach (var observer in observers.ToArray())
         if (observers.Contains(observer))
            observer.OnCompleted();

      observers.Clear();
   }
}
Public Class LocationTracker : Implements IObservable(Of Location)

   Public Sub New()
      observers = New List(Of IObserver(Of Location))
   End Sub

   Private observers As List(Of IObserver(Of Location))

   Public Function Subscribe(ByVal observer As System.IObserver(Of Location)) As System.IDisposable _
                            Implements System.IObservable(Of Location).Subscribe
      If Not observers.Contains(observer) Then
         observers.Add(observer)
      End If
      Return New Unsubscriber(observers, observer)
   End Function

   Private Class Unsubscriber : Implements IDisposable
      Private _observers As List(Of IObserver(Of Location))
      Private _observer As IObserver(Of Location)

      Public Sub New(ByVal observers As List(Of IObserver(Of Location)), ByVal observer As IObserver(Of Location))
         Me._observers = observers
         Me._observer = observer
      End Sub

      Public Sub Dispose() Implements IDisposable.Dispose
         If _observer IsNot Nothing AndAlso _observers.Contains(_observer) Then
            _observers.Remove(_observer)
         End If
      End Sub
   End Class

   Public Sub TrackLocation(ByVal loc As Nullable(Of Location))
      For Each observer In observers
         If Not loc.HasValue Then
            observer.OnError(New LocationUnknownException())
         Else
            observer.OnNext(loc.Value)
         End If
      Next
   End Sub

   Public Sub EndTransmission()
      For Each observer In observers.ToArray()
         If observers.Contains(observer) Then observer.OnCompleted()
      Next
      observers.Clear()
   End Sub
End Class

如果 Location 值为 null ,则该 TrackLocation 方法将实例化 LocationNotFoundException 对象,如下例所示。If the Location value is null, the TrackLocation method instantiates a LocationNotFoundException object, which is shown in the following example. 然后,它调用每个观察程序的 OnError 方法并向其传递 LocationNotFoundException 对象。It then calls each observer's OnError method and passes it the LocationNotFoundException object. 请注意, LocationNotFoundException 从派生, Exception 但不添加任何新成员。Note that LocationNotFoundException derives from Exception but does not add any new members.

public class LocationUnknownException : Exception
{
   internal LocationUnknownException()
   { }
}
Public Class LocationUnknownException : Inherits Exception
   Friend Sub New()
   End Sub
End Class

观察者通过调用其方法来注册以接收来自对象的通知 TrackLocation IObservable<T>.Subscribe ,该方法将对观察者对象的引用分配给私有泛型 List<T> 对象。Observers register to receive notifications from a TrackLocation object by calling its IObservable<T>.Subscribe method, which assigns a reference to the observer object to a private generic List<T> object. 方法返回一个 Unsubscriber 对象,该对象是一个 IDisposable 实现,它使观察程序可以停止接收通知。The method returns an Unsubscriber object, which is an IDisposable implementation that enables observers to stop receiving notifications. LocationTracker类还包含 EndTransmission 方法。The LocationTracker class also includes an EndTransmission method. 当没有更多的位置数据可用时,方法会调用每个观察程序的 OnCompleted 方法,然后清除观察程序的内部列表。When no further location data is available, the method calls each observer's OnCompleted method and then clears the internal list of observers.

然后,以下代码实例化提供程序和观察程序。The following code then instantiates the provider and the observer.

using System;

class Program
{
   static void Main(string[] args)
   {
      // Define a provider and two observers.
      LocationTracker provider = new LocationTracker();
      LocationReporter reporter1 = new LocationReporter("FixedGPS");
      reporter1.Subscribe(provider);
      LocationReporter reporter2 = new LocationReporter("MobileGPS");
      reporter2.Subscribe(provider);

      provider.TrackLocation(new Location(47.6456, -122.1312));
      reporter1.Unsubscribe();
      provider.TrackLocation(new Location(47.6677, -122.1199));
      provider.TrackLocation(null);
      provider.EndTransmission();
   }
}
// The example displays output similar to the following:
//      FixedGPS: The current location is 47.6456, -122.1312
//      MobileGPS: The current location is 47.6456, -122.1312
//      MobileGPS: The current location is 47.6677, -122.1199
//      MobileGPS: The location cannot be determined.
//      The Location Tracker has completed transmitting data to MobileGPS.
Module Module1
   Dim provider As LocationTracker

   Sub Main()
      ' Define a provider and two observers.
      provider = New LocationTracker()
      Dim reporter1 As New LocationReporter("FixedGPS")
      reporter1.Subscribe(provider)
      Dim reporter2 As New LocationReporter("MobileGPS")
      reporter2.Subscribe(provider)

      provider.TrackLocation(New Location(47.6456, -122.1312))
      reporter1.Unsubscribe()
      provider.TrackLocation(New Location(47.6677, -122.1199))
      provider.TrackLocation(Nothing)
      provider.EndTransmission()
   End Sub
End Module
' The example displays output similar to the following:
'       FixedGPS: The current location is 47.6456, -122.1312
'       MobileGPS: The current location is 47.6456, -122.1312
'       MobileGPS: The current location is 47.6677, -122.1199
'       MobileGPS: The location cannot be determined.
'       The Location Tracker has completed transmitting data to MobileGPS.

注解

IObserver<T>IObservable<T> 接口为基于推送的通知(也称为观察者设计模式)提供通用机制。The IObserver<T> and IObservable<T> interfaces provide a generalized mechanism for push-based notification, also known as the observer design pattern. IObservable<T>接口表示类,该类 (提供程序) 发送通知; IObserver<T> 接口表示在观察程序) (接收它们的类。The IObservable<T> interface represents the class that sends notifications (the provider); the IObserver<T> interface represents the class that receives them (the observer). T 表示提供通知信息的类。T represents the class that provides the notification information.

IObserver<T>实现安排,通过将一个 IObservable<T> 实例传递给提供程序的方法,从提供程序 (实现) 接收通知 IObservable<T>.SubscribeAn IObserver<T> implementation arranges to receive notifications from a provider (an IObservable<T> implementation) by passing an instance of itself to the provider's IObservable<T>.Subscribe method. 此方法返回一个 IDisposable 对象,该对象可用于在提供程序完成发送通知之前取消订阅观察程序。This method returns an IDisposable object that can be used to unsubscribe the observer before the provider finishes sending notifications.

IObserver<T>接口定义了观察程序必须实现的以下三种方法:The IObserver<T> interface defines the following three methods that the observer must implement:

  • OnNext方法,通常由提供程序调用以向观察者提供新数据或状态信息。The OnNext method, which is typically called by the provider to supply the observer with new data or state information.

  • OnError方法,通常由提供程序调用,以指示数据不可用、不可访问或已损坏,或者提供程序遇到了一些其他错误情况。The OnError method, which is typically called by the provider to indicate that data is unavailable, inaccessible, or corrupted, or that the provider has experienced some other error condition.

  • OnCompleted方法,通常由提供程序调用,以指示已完成向观察者发送通知。The OnCompleted method, which is typically called by the provider to indicate that it has finished sending notifications to observers.

方法

OnCompleted()

通知观察者提供程序已完成发送基于推送的通知。Notifies the observer that the provider has finished sending push-based notifications.

OnError(Exception)

通知观察者提供程序遇到错误情况。Notifies the observer that the provider has experienced an error condition.

OnNext(T)

向观察者提供新数据。Provides the observer with new data.

适用于

另请参阅