EventHandler Delegar

Definição

Representa o método que tratará um evento que não tem nenhum dado de evento.Represents the method that will handle an event that has no event data.

public delegate void EventHandler(System::Object ^ sender, EventArgs ^ e);
[System.Runtime.InteropServices.ComVisible(true)]
[System.Serializable]
public delegate void EventHandler(object sender, EventArgs e);
type EventHandler = delegate of obj * EventArgs -> unit
Public Delegate Sub EventHandler(sender As Object, e As EventArgs)

Parâmetros

sender
Object

A fonte do evento.The source of the event.

e
EventArgs

Um objeto que não contém nenhum dado de eventos.An object that contains no event data.

Herança
EventHandler
Atributos

Exemplos

O exemplo a seguir mostra um evento ThresholdReached chamado que está associado a EventHandler um delegado.The following example shows an event named ThresholdReached that is associated with an EventHandler delegate. O método atribuído ao EventHandler delegado é chamado OnThresholdReached no método.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

Comentários

O modelo de evento na .NET Framework se baseia em ter um delegado de evento que conecta um evento com seu manipulador.The event model in the .NET Framework is based on having an event delegate that connects an event with its handler. Para gerar um evento, são necessários dois elementos:To raise an event, two elements are needed:

  • Um delegado que identifica o método que fornece a resposta ao evento.A delegate that identifies the method that provides the response to the event.

  • Opcionalmente, uma classe que contém os dados do evento, se o evento fornecer dados.Optionally, a class that holds the event data, if the event provides data.

O delegado é um tipo que define uma assinatura, ou seja, o tipo de valor de retorno e os tipos de lista de parâmetros para um método.The delegate is a type that defines a signature, that is, the return value type and parameter list types for a method. Você pode usar o tipo delegado para declarar uma variável que pode se referir a qualquer método com a mesma assinatura do delegado.You can use the delegate type to declare a variable that can refer to any method with the same signature as the delegate.

A assinatura padrão de um delegado de manipulador de eventos define um método que não retorna um valor.The standard signature of an event handler delegate defines a method that does not return a value. O primeiro parâmetro do método é do tipo Object e refere-se à instância que gera o evento.This method's first parameter is of type Object and refers to the instance that raises the event. Seu segundo parâmetro é derivado do tipo EventArgs e contém os dados do evento.Its second parameter is derived from type EventArgs and holds the event data. Se o evento não gerar dados de evento, o segundo parâmetro será simplesmente o valor do EventArgs.Empty campo.If the event does not generate event data, the second parameter is simply the value of the EventArgs.Empty field. Caso contrário, o segundo parâmetro é um tipo derivado EventArgs de e fornece quaisquer campos ou Propriedades necessários para manter os dados do evento.Otherwise, the second parameter is a type derived from EventArgs and supplies any fields or properties needed to hold the event data.

O EventHandler delegado é um delegado predefinido que representa especificamente um método de manipulador de eventos para um evento que não gera dados.The EventHandler delegate is a predefined delegate that specifically represents an event handler method for an event that does not generate data. Se o evento gerar dados, você deverá usar a classe delegate EventHandler<TEventArgs> genérica.If your event does generate data, you must use the generic EventHandler<TEventArgs> delegate class.

Para associar o evento ao método que manipulará o evento, adicione uma instância do delegado ao evento.To associate the event with the method that will handle the event, add an instance of the delegate to the event. O manipulador de eventos é chamado sempre que o evento ocorre, a menos que você remova o representante.The event handler is called whenever the event occurs, unless you remove the delegate.

Para obter mais informações sobre delegados de manipulador de eventos, consulte manipulando e gerando eventos.For more information about event handler delegates, see Handling and Raising Events.

Métodos de Extensão

GetMethodInfo(Delegate)

Obtém um objeto que representa o método representado pelo delegado especificado.Gets an object that represents the method represented by the specified delegate.

Aplica-se a

Veja também