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

Definice

Poskytuje mechanismus pro příjem oznámení založených na nabízených oznámeních.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)

Parametry typu

T

Objekt, který poskytuje informace o oznámení.The object that provides notification information.

Odvozené

Příklady

Následující příklad znázorňuje vzor návrhu pozorovatele.The following example illustrates the observer design pattern. Definuje Location třídu, která obsahuje informace o zeměpisné šířce a délce.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 TřídaIObserver<T> poskytuje implementaci.The LocationReporter class provides the IObserver<T> implementation. V konzole se zobrazí informace o aktuálním umístění.It displays information about the current location to the console. Jeho konstruktor obsahuje name parametr, který LocationReporter umožňuje instanci identifikovat sama sebe ve svém výstupním řetězci.Its constructor includes a name parameter, which allows the LocationReporter instance to identify itself in its string output. Obsahuje Subscribe také metodu, která zabalí volání Subscribe metody poskytovatele.It also includes a Subscribe method, which wraps a call to the provider's Subscribe method. To umožňuje metodě přiřadit vrácený IDisposable odkaz na soukromou proměnnou.This enables the method to assign the returned IDisposable reference to a private variable. Třída také Unsubscribe obsahuje metodu,kterávoláIObservable<T>.Subscribe IDisposable.Dispose metodu objektu vráceného metodou. LocationReporterThe LocationReporter class also includes an Unsubscribe method, which calls the IDisposable.Dispose method of the object returned by the IObservable<T>.Subscribe method. LocationReporter Třída definuje následující kód.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 TřídaIObservable<T> poskytuje implementaci.The LocationTracker class provides the IObservable<T> implementation. Jeho TrackLocation metoda je předána objektu Location s možnou hodnotou null, který obsahuje data o zeměpisné šířce a délce.Its TrackLocation method is passed a nullable Location object that contains the latitude and longitude data. Location Pokud hodnota nullnení ,TrackLocationMetoda volá metoduOnNext každého pozorovatele.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

Pokud je Location nullhodnota LocationNotFoundException , TrackLocation metoda vytvoří instanci objektu, který je zobrazen v následujícím příkladu.If the Location value is null, the TrackLocation method instantiates a LocationNotFoundException object, which is shown in the following example. Pak volá každou OnError metodu pozorovatele a předá LocationNotFoundException ji objektu.It then calls each observer's OnError method and passes it the LocationNotFoundException object. Všimněte si LocationNotFoundException , že se Exception odvozují z, ale nepřidává žádné nové členy.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

Pozorovatelé se registrují pro příjem TrackLocation oznámení z objektu IObservable<T>.Subscribe voláním metody, která přiřadí odkaz na objekt pozorovatele na privátní obecný List<T> objekt.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. Metoda vrátí Unsubscriber objekt, což IDisposable je implementace umožňující pozorovatelům zastavit příjem oznámení.The method returns an Unsubscriber object, which is an IDisposable implementation that enables observers to stop receiving notifications. LocationTracker Třída takéEndTransmission obsahuje metodu.The LocationTracker class also includes an EndTransmission method. Pokud nejsou k dispozici žádná další data o umístění, metoda volá každou OnCompleted metodu pozorovatele a pak vymaže interní seznam pozorovatelů.When no further location data is available, the method calls each observer's OnCompleted method and then clears the internal list of observers.

Následující kód potom vytvoří instanci poskytovatele a pozorovatele.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.

Poznámky

Rozhraní IObserver<T> aIObservable<T> poskytují zobecněný mechanizmus oznámení na základě nabízených oznámení, označovaného také jako návrhový vzor pozorovatele.The IObserver<T> and IObservable<T> interfaces provide a generalized mechanism for push-based notification, also known as the observer design pattern. Rozhraní představuje třídu, která odesílá oznámení (poskytovatel) IObserver<T> ; rozhraní představuje třídu, která je přijímá (pozorovatel). IObservable<T>The IObservable<T> interface represents the class that sends notifications (the provider); the IObserver<T> interface represents the class that receives them (the observer). Tpředstavuje třídu, která poskytuje informace o oznámení.T represents the class that provides the notification information.

Implementace se uspořádá pro příjem oznámení od poskytovatele IObservable<T> (implementace) předáním instance IObservable<T>.Subscribe sama sobě metodě poskytovatele. IObserver<T>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. Tato metoda vrátí IDisposable objekt, který lze použít k odhlášení odběru pozorovatele předtím, než poskytovatel dokončí odesílání oznámení.This method returns an IDisposable object that can be used to unsubscribe the observer before the provider finishes sending notifications.

IObserver<T> Rozhraní definuje následující tři metody, které musí pozorovatel implementovat:The IObserver<T> interface defines the following three methods that the observer must implement:

  • OnNext Metoda, která je obvykle volána poskytovatelem k poskytnutí pozorovatele k novým informacím o datech nebo stavu.The OnNext method, which is typically called by the provider to supply the observer with new data or state information.

  • OnError Metoda, která je obvykle volána poskytovatelem, aby označovala, že data nejsou k dispozici, nejsou k dispozici nebo jsou poškozena nebo že došlo k nějakému chybě poskytovatele.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 Metoda, která je obvykle volána poskytovatelem, aby označovala, že dokončila odesílání oznámení pozorovatelům.The OnCompleted method, which is typically called by the provider to indicate that it has finished sending notifications to observers.

Metody

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

Upozorní pozorovatele, že poskytovatel dokončil odesílání oznámení na základě nabízených oznámení.Notifies the observer that the provider has finished sending push-based notifications.

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

Upozorní pozorovatele, že došlo k chybě v poskytovateli.Notifies the observer that the provider has experienced an error condition.

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

Poskytuje pozorovatele s novými daty.Provides the observer with new data.

Platí pro

Viz také