EventHandler Delegat

Definition

public delegate void EventHandler(System::Object ^ sender, EventArgs ^ e);

public delegate void EventHandler(object sender, EventArgs e);

public delegate void EventHandler(object? sender, EventArgs e);

[System.Serializable]
public delegate void EventHandler(object sender, EventArgs e);

[System.Serializable]
[System.Runtime.InteropServices.ComVisible(true)]
public delegate void EventHandler(object sender, EventArgs e);

type EventHandler = delegate of obj * EventArgs -> unit

[<System.Serializable>]
type EventHandler = delegate of obj * EventArgs -> unit

[<System.Serializable>]
[<System.Runtime.InteropServices.ComVisible(true)>]
type EventHandler = delegate of obj * EventArgs -> unit

Public Delegate Sub EventHandler(sender As Object, e As EventArgs)

Parameter

Vererbung

Object

Delegate

EventHandler

Attribute

SerializableAttribute ComVisibleAttribute

Beispiele

Das folgende Beispiel zeigt ein Ereignis mit dem Namen ThresholdReached , das einem-Delegaten zugeordnet ist EventHandler .The following example shows an event named ThresholdReached that is associated with an EventHandler delegate. Die dem Delegaten zugewiesene Methode EventHandler wird in der- OnThresholdReached Methode aufgerufen.The method assigned to the EventHandler delegate is called in the OnThresholdReached method.

using namespace System;

public ref class ThresholdReachedEventArgs : public EventArgs
{
   public:
      property int Threshold;
      property DateTime TimeReached;
};

public ref class Counter
{
   private:
      int threshold;
      int total;

   public:
      Counter() {};

      Counter(int passedThreshold)
      {
         threshold = passedThreshold;
      }

      void Add(int x)
      {
          total += x;
          if (total >= threshold) {
             ThresholdReachedEventArgs^ args = gcnew ThresholdReachedEventArgs();
             args->Threshold = threshold;
             args->TimeReached = DateTime::Now;
             OnThresholdReached(args);
          }
      }

      event EventHandler<ThresholdReachedEventArgs^>^ ThresholdReached;

   protected:
      virtual void OnThresholdReached(ThresholdReachedEventArgs^ e)
      {
         ThresholdReached(this, e);
      }
};

public ref class SampleHandler
{
   public:
      static void c_ThresholdReached(Object^ sender, ThresholdReachedEventArgs^ e)
      {
         Console::WriteLine("The threshold of {0} was reached at {1}.",
                            e->Threshold,  e->TimeReached);
         Environment::Exit(0);
      }
};

void main()
{
   Counter^ c = gcnew Counter((gcnew Random())->Next(10));
   c->ThresholdReached += gcnew EventHandler<ThresholdReachedEventArgs^>(SampleHandler::c_ThresholdReached);

   Console::WriteLine("press 'a' key to increase total");
   while (Console::ReadKey(true).KeyChar == 'a') {
      Console::WriteLine("adding one");
      c->Add(1);
   }
}

using System;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            Counter c = new Counter(new Random().Next(10));
            c.ThresholdReached += c_ThresholdReached;

            Console.WriteLine("press 'a' key to increase total");
            while (Console.ReadKey(true).KeyChar == 'a')
            {
                Console.WriteLine("adding one");
                c.Add(1);
            }
        }

        static void c_ThresholdReached(object sender, ThresholdReachedEventArgs e)
        {
            Console.WriteLine("The threshold of {0} was reached at {1}.", e.Threshold,  e.TimeReached);
            Environment.Exit(0);
        }
    }

    class Counter
    {
        private int threshold;
        private int total;

        public Counter(int passedThreshold)
        {
            threshold = passedThreshold;
        }

        public void Add(int x)
        {
            total += x;
            if (total >= threshold)
            {
                ThresholdReachedEventArgs args = new ThresholdReachedEventArgs();
                args.Threshold = threshold;
                args.TimeReached = DateTime.Now;
                OnThresholdReached(args);
            }
        }

        protected virtual void OnThresholdReached(ThresholdReachedEventArgs e)
        {
            EventHandler<ThresholdReachedEventArgs> handler = ThresholdReached;
            if (handler != null)
            {
                handler(this, e);
            }
        }

        public event EventHandler<ThresholdReachedEventArgs> ThresholdReached;
    }

    public class ThresholdReachedEventArgs : EventArgs
    {
        public int Threshold { get; set; }
        public DateTime TimeReached { get; set; }
    }
}

Module Module1

    Sub Main()
        Dim c As Counter = New Counter(New Random().Next(10))
        AddHandler c.ThresholdReached, AddressOf c_ThresholdReached

        Console.WriteLine("press 'a' key to increase total")
        While Console.ReadKey(True).KeyChar = "a"
            Console.WriteLine("adding one")
            c.Add(1)
        End While
    End Sub

    Sub c_ThresholdReached(sender As Object, e As ThresholdReachedEventArgs)
        Console.WriteLine("The threshold of {0} was reached at {1}.", e.Threshold, e.TimeReached)
        Environment.Exit(0)
    End Sub
End Module

Class Counter
    Private threshold As Integer
    Private total As Integer

    Public Sub New(passedThreshold As Integer)
        threshold = passedThreshold
    End Sub

    Public Sub Add(x As Integer)
        total = total + x
        If (total >= threshold) Then
            Dim args As ThresholdReachedEventArgs = New ThresholdReachedEventArgs()
            args.Threshold = threshold
            args.TimeReached = DateTime.Now
            OnThresholdReached(args)
        End If
    End Sub

    Protected Overridable Sub OnThresholdReached(e As ThresholdReachedEventArgs)
        RaiseEvent ThresholdReached(Me, e)
    End Sub

    Public Event ThresholdReached As EventHandler(Of ThresholdReachedEventArgs)
End Class

Class ThresholdReachedEventArgs
    Inherits EventArgs

    Public Property Threshold As Integer
    Public Property TimeReached As DateTime
End Class

Hinweise

Das Ereignis Modell in der .NET Framework basiert auf einem Ereignis Delegaten, der ein Ereignis mit seinem Handler verbindet.The event model in the .NET Framework is based on having an event delegate that connects an event with its handler. Um ein Ereignis aufzurichten, sind zwei Elemente erforderlich:To raise an event, two elements are needed:

• Ein Delegat, der die Methode identifiziert, die die Antwort auf das Ereignis bereitstellt.A delegate that identifies the method that provides the response to the event.

• Optional eine Klasse, die die Ereignisdaten enthält, wenn das Ereignisdaten bereitstellt.Optionally, a class that holds the event data, if the event provides data.

Der Delegat ist ein Typ, der eine Signatur definiert, d. h. den Rückgabe Werttyp und die Parameterlisten Typen für eine Methode.The delegate is a type that defines a signature, that is, the return value type and parameter list types for a method. Sie können den Delegattyp verwenden, um eine Variable zu deklarieren, die auf eine beliebige Methode mit der gleichen Signatur wie der Delegat verweisen kann.You can use the delegate type to declare a variable that can refer to any method with the same signature as the delegate.

Die Standard Signatur eines Ereignishandlerdelegaten definiert eine Methode, die keinen Wert zurückgibt.The standard signature of an event handler delegate defines a method that does not return a value. Der erste Parameter dieser Methode ist vom Typ Object und verweist auf die Instanz, die das Ereignis auslöst.This method's first parameter is of type Object and refers to the instance that raises the event. Der zweite Parameter wird vom-Typ abgeleitet EventArgs und enthält die Ereignisdaten.Its second parameter is derived from type EventArgs and holds the event data. Wenn das Ereignis keine Ereignisdaten generiert, ist der zweite Parameter einfach der Wert des EventArgs.Empty Felds.If the event does not generate event data, the second parameter is simply the value of the EventArgs.Empty field. Andernfalls ist der zweite Parameter ein von abgeleiteter Typ, der EventArgs alle Felder oder Eigenschaften bereitstellt, die zum Speichern der Ereignisdaten benötigt werden.Otherwise, the second parameter is a type derived from EventArgs and supplies any fields or properties needed to hold the event data.

Der Delegat EventHandler ist ein vordefinierter Delegat, der speziell eine Ereignishandlermethode für ein Ereignis darstellt, das keine Daten generiert.The EventHandler delegate is a predefined delegate that specifically represents an event handler method for an event that does not generate data. Wenn das Ereignisdaten generiert, müssen Sie die generische EventHandler<TEventArgs> Delegatklasse verwenden.If your event does generate data, you must use the generic EventHandler<TEventArgs> delegate class.

Fügen Sie dem-Ereignis eine Instanz des-Delegaten hinzu, um das-Ereignis der Methode zuzuordnen, die das-Ereignis behandelt.To associate the event with the method that will handle the event, add an instance of the delegate to the event. Der Ereignishandler wird bei jedem Eintreten des Ereignisses aufgerufen, sofern der Delegat nicht entfernt wird.The event handler is called whenever the event occurs, unless you remove the delegate.

Weitere Informationen zu Ereignishandlerdelegaten finden Sie unter behandeln und Auswerfen von Ereignissen.For more information about event handler delegates, see Handling and Raising Events.

Erweiterungsmethoden

Gilt für:

Siehe auch

• EventHandler<TEventArgs>
• EventArgs
• Delegate
• Behandeln und Auslösen von EreignissenHandling and Raising Events
• Vorgehensweise: Auslösen und Verarbeiten von EreignissenHow to: Raise and Consume Events
• Ereignisse (Visual Basic)Events (Visual Basic)
• Ereignisse (C#-Programmierhandbuch)Events (C# Programming Guide)
• Übersicht über Ereignisse und Routingereignisse (Windows Store-Apps)Events and routed events overview (Windows store apps)