IObserver<T> IObserver<T> IObserver<T> IObserver<T> Interface

Definizione

Fornisce un meccanismo per ricevere notifiche basate su push.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)

Parametri di tipo

T

Oggetto che fornisce informazioni di notifica.The object that provides notification information.

Derivato

Esempi

Nell'esempio seguente viene illustrato il modello di progettazione Observer.The following example illustrates the observer design pattern. Definisce una classe Location che contiene informazioni sulla latitudine e la longitudine.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

La LocationReporter classe fornisce l' IObserver<T> implementazione di.The LocationReporter class provides the IObserver<T> implementation. Visualizza le informazioni relative alla posizione corrente nella console.It displays information about the current location to the console. Il costruttore include un name parametro, che LocationReporter consente all'istanza di identificare se stessa nell'output della stringa.Its constructor includes a name parameter, which allows the LocationReporter instance to identify itself in its string output. Include anche un Subscribe metodo che esegue il wrapping di una chiamata al Subscribe metodo del provider.It also includes a Subscribe method, which wraps a call to the provider's Subscribe method. Ciò consente al metodo di assegnare il riferimento IDisposable restituito a una variabile privata.This enables the method to assign the returned IDisposable reference to a private variable. La LocationReporter classe include anche un Unsubscribe metodo, che chiama il IDisposable.Dispose metodo dell'oggetto restituito dal IObservable<T>.Subscribe metodo.The LocationReporter class also includes an Unsubscribe method, which calls the IDisposable.Dispose method of the object returned by the IObservable<T>.Subscribe method. Il codice seguente definisce la LocationReporter classe.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

La LocationTracker classe fornisce l' IObservable<T> implementazione di.The LocationTracker class provides the IObservable<T> implementation. Al metodo viene passato un oggetto Location nullable che contiene i dati di latitudine e longitudine. TrackLocationIts TrackLocation method is passed a nullable Location object that contains the latitude and longitude data. Se il Location valore non nullè, il TrackLocation metodo chiama il OnNext metodo di ogni osservatore.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

Se il Location valore è null, il TrackLocation metodo crea un'istanza LocationNotFoundException di un oggetto, come illustrato nell'esempio seguente.If the Location value is null, the TrackLocation method instantiates a LocationNotFoundException object, which is shown in the following example. Chiama quindi il metodo di OnError ogni osservatore e lo passa all' LocationNotFoundException oggetto.It then calls each observer's OnError method and passes it the LocationNotFoundException object. Si noti LocationNotFoundException che deriva da Exception ma non aggiunge nuovi membri.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

Gli osservatori eseguono la registrazione per ricevere TrackLocation notifiche da un oggetto IObservable<T>.Subscribe chiamando il relativo metodo, che assegna un riferimento all'oggetto Observer a un oggetto generico List<T> privato.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. Il metodo restituisce un Unsubscriber oggetto, che è un' IDisposable implementazione che consente agli osservatori di arrestare la ricezione delle notifiche.The method returns an Unsubscriber object, which is an IDisposable implementation that enables observers to stop receiving notifications. La LocationTracker classe include anche un EndTransmission metodo.The LocationTracker class also includes an EndTransmission method. Quando non sono disponibili ulteriori dati sulla posizione, il metodo chiama il metodo di OnCompleted ogni osservatore e quindi cancella l'elenco interno di osservatori.When no further location data is available, the method calls each observer's OnCompleted method and then clears the internal list of observers.

Il codice seguente crea quindi un'istanza del provider e dell'osservatore.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.

Commenti

Le IObserver<T> interfacce IObservable<T> e forniscono un meccanismo generalizzato per le notifiche basate su push, noto anche come modello di progettazione Observer.The IObserver<T> and IObservable<T> interfaces provide a generalized mechanism for push-based notification, also known as the observer design pattern. L' IObservable<T> interfaccia rappresenta la classe che invia le notifiche (il provider); IObserver<T> l'interfaccia rappresenta la classe che li riceve (l'osservatore).The IObservable<T> interface represents the class that sends notifications (the provider); the IObserver<T> interface represents the class that receives them (the observer). Trappresenta la classe che fornisce le informazioni di notifica.T represents the class that provides the notification information.

Un' IObserver<T> implementazione dispone di per ricevere notifiche da un provider (un' IObservable<T> implementazione di) passando un'istanza di IObservable<T>.Subscribe se stessa al metodo del provider.An 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. Questo metodo restituisce un IDisposable oggetto che può essere utilizzato per annullare la sottoscrizione dell'Observer prima del completamento dell'invio delle notifiche da parte del provider.This method returns an IDisposable object that can be used to unsubscribe the observer before the provider finishes sending notifications.

L' IObserver<T> interfaccia definisce i tre metodi seguenti che devono essere implementati dall'Observer:The IObserver<T> interface defines the following three methods that the observer must implement:

  • Il OnNext metodo, che in genere viene chiamato dal provider per fornire all'osservatore nuove informazioni sui dati o sullo stato.The OnNext method, which is typically called by the provider to supply the observer with new data or state information.

  • Il OnError metodo, che in genere viene chiamato dal provider per indicare che i dati non sono disponibili, inaccessibili o danneggiati o che il provider ha riscontrato altre condizioni di errore.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.

  • Il OnCompleted metodo, che in genere viene chiamato dal provider per indicare che ha completato l'invio di notifiche agli osservatori.The OnCompleted method, which is typically called by the provider to indicate that it has finished sending notifications to observers.

Metodi

OnCompleted() OnCompleted() OnCompleted() OnCompleted()

Notifica all'osservatore che il provider ha terminato di inviare notifiche basate su push.Notifies the observer that the provider has finished sending push-based notifications.

OnError(Exception) OnError(Exception) OnError(Exception) OnError(Exception)

Notifica all'osservatore che il provider ha riscontrato una condizione di errore.Notifies the observer that the provider has experienced an error condition.

OnNext(T) OnNext(T) OnNext(T) OnNext(T)

Fornisce nuovi dati all'osservatore.Provides the observer with new data.

Si applica a

Vedi anche