IObserver<T> 介面

定義

命名空間:: System

組件:: mscorlib.dll, System.Runtime.dll

組件:: netstandard.dll, System.Runtime.dll

組件:: System.Runtime.dll

組件:: mscorlib.dll

組件:: netstandard.dll

來源:: IObserver.cs

來源:: IObserver.cs

來源:: ThreadPoolBoundHandle.Unix.cs

重要

部分資訊涉及發行前產品，在發行之前可能會有大幅修改。 Microsoft 對此處提供的資訊，不做任何明確或隱含的瑕疵擔保。

提供接收推播通知的機制。

generic <typename T>
public interface class IObserver

public interface IObserver<in T>

type IObserver<'T> = interface

Public Interface IObserver(Of In T)

類型參數

T

提供通知資訊的物件。

這是反變數的型別參數。也就是說，您可以使用您指定的類型，或衍生程度較低的任何類型。如需共變數與反變數的詳細資訊，請參閱泛型中的共變數與反變數。

衍生: Microsoft.Extensions.DiagnosticAdapter.DiagnosticSourceAdapter

System.Web.Hosting.LowPhysicalMemoryObserver

System.Web.Hosting.RecycleLimitObserver

範例

以下範例說明觀察者設計模式。它定義了一個 Location 包含緯度與經度資訊的類別。

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; } }
}

[<Struct>]
type Location =
    { Latitude: double
      Longitude: double }

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

該 LocationReporter 類別提供 IObserver<T> 實作。它會顯示目前位置的資訊給主控台。其建構子包含一個 name 參數，允許實 LocationReporter 例在其字串輸出中識別自身。它還包含一個 Subscribe 方法，將呼叫包裝到提供者的方法 Subscribe 。這使得該方法能夠將回傳 IDisposable 的參考指派給私有變數。該 LocationReporter 類別也包含一個 Unsubscribe 方法，該方法會呼叫 IDisposable.Dispose 該方法回傳 IObservable<T>.Subscribe 的物件的方法。以下程式碼定義了這個 LocationReporter 類別。

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();
   }
}

open System

type LocationReporter(name) =
    let mutable unsubscriber = Unchecked.defaultof<IDisposable>

    member _.Name = name

    member this.Subscribe(provider: IObservable<Location>) =
        if provider <> null then
            unsubscriber <- provider.Subscribe this

    member _.Unsubscribe() =
        unsubscriber.Dispose()

    interface IObserver<Location> with
        member this.OnCompleted() =
            printfn $"The Location Tracker has completed transmitting data to {name}."
            this.Unsubscribe()

        member _.OnError(_) =
            printfn $"{name}: The location cannot be determined."

        member _.OnNext(value) =
            printfn $"{name}: The current location is {value.Latitude}, {value.Longitude}"

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

該 LocationTracker 類別提供 IObservable<T> 實作。其 TrackLocation 方法傳遞一個可 Location 空的物件，該物件包含緯度與經度資料。若Location值不null為，該方法呼叫TrackLocationOnNext每個觀察者的方法。

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();
   }
}

type Unsubscriber(observers: ResizeArray<IObserver<Location>>, observer: IObserver<Location>) =
    interface IDisposable with
        member _.Dispose() =
            if observer <> null && observers.Contains observer then
                observers.Remove observer |> ignore

type LocationTracker() =
    let observers = ResizeArray<IObserver<Location>>()

    interface IObservable<Location> with
        member _.Subscribe(observer) =
            if observers.Contains observer |> not then
                observers.Add observer
            new Unsubscriber(observers, observer)

    member _.TrackLocation(loc: Nullable<Location>) =
        for observer in observers do
            if not loc.HasValue then
                observer.OnError LocationUnknownException
            else
                observer.OnNext loc.Value

    member _.EndTransmission() =
        for observer in observers.ToArray() do
            if observers.Contains observer then
                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

若值Location為，該null方法實例化一個TrackLocation物件，LocationNotFoundException如下範例所示。接著它呼叫每位觀察者的方法 OnError ，並將該 LocationNotFoundException 物件傳給該方法。注意從LocationNotFoundExceptionException衍生，但不新增任何成員。

public class LocationUnknownException : Exception
{
   internal LocationUnknownException()
   { }
}

exception LocationUnknownException

Public Class LocationUnknownException : Inherits Exception
   Friend Sub New()
   End Sub
End Class

觀察者透過 TrackLocation 呼叫 IObservable<T>.Subscribe 物件的方法註冊接收通知，該方法會將觀察者物件的參考指派給一個私有的泛型 List<T> 物件。該方法回傳一個 Unsubscriber 物件，這是一個 IDisposable 實作，使觀察者能夠停止接收通知。這 LocationTracker 堂課也包含一種 EndTransmission 方法。當沒有其他位置資料可用時，該方法會呼叫每位觀察者的方法 OnCompleted ，然後清除內部觀察者清單。

接著，以下程式碼實例化提供者與觀察者。

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.

open System

// Define a provider and two observers.
let provider = LocationTracker()
let reporter1 = LocationReporter "FixedGPS"
reporter1.Subscribe provider
let reporter2 = LocationReporter "MobileGPS"
reporter2.Subscribe provider

provider.TrackLocation { Latitude = 47.6456; Longitude = -122.1312 }
reporter1.Unsubscribe()
provider.TrackLocation { Latitude = 47.6677; Longitude = -122.1199 }
provider.TrackLocation(Nullable())
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.

備註

IObserver<T>與IObservable<T>介面提供了一種通用的推播式通知機制，也稱為觀察者設計模式。介面 IObservable<T> 代表發送通知的類別（提供者）; IObserver<T> 介面代表接收通知的類別（觀察者）。 T 代表提供通知資訊的類別。

實IObserver<T>作透過將自身實例傳遞給提供者的方法IObservable<T>來安排接收來自提供者（實IObservable<T>.Subscribe作）的通知。此方法回傳一個 IDisposable 物件，可用於在提供者完成通知發送前取消訂閱觀察者。

介面 IObserver<T> 定義了觀察者必須實作的三種方法：

此 OnNext 方法通常由提供者呼叫，以提供觀察者新的資料或狀態資訊。
OnError此方法通常由提供者呼叫，表示資料無法取得、無法存取或損壞，或提供者遇到其他錯誤狀況。
OnCompleted這個方法通常是提供者呼叫，表示已完成向觀察者發送通知。

方法

名稱	Description
OnCompleted()	通知觀察者提供者已完成推送通知的發送。
OnError(Exception)	通知觀察者提供者發生錯誤狀況。
OnNext(T)	為觀察者提供新資料。

適用於

另請參閱

IObservable<T>

意見反應

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