EventHandler EventHandler EventHandler EventHandler Delegate

定义

表示将处理不包含事件数据的事件的方法。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)

参数

sender
Object Object Object Object

事件源。The source of the event.

e
EventArgs EventArgs EventArgs EventArgs

不包含事件数据的对象。An object that contains no event data.

继承
EventHandlerEventHandlerEventHandlerEventHandler
属性

示例

下面的示例演示一个名ThresholdReached为的事件, 该事件与一个EventHandler委托相关联。The following example shows an event named ThresholdReached that is associated with an EventHandler delegate. 分配EventHandler给委托的方法OnThresholdReached在方法中调用。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

注解

.NET Framework 中的事件模型基于事件委托, 该委托将事件与其处理程序连接。The event model in the .NET Framework is based on having an event delegate that connects an event with its handler. 若要引发事件, 需要两个元素:To raise an event, two elements are needed:

  • 一个委托, 该委托标识向事件提供响应的方法。A delegate that identifies the method that provides the response to the event.

  • 如果事件提供数据, 则为包含事件数据的类 (可选)。Optionally, a class that holds the event data, if the event provides data.

委托是一种类型, 它定义签名, 即方法的返回值类型和参数列表类型。The delegate is a type that defines a signature, that is, the return value type and parameter list types for a method. 您可以使用委托类型声明一个变量, 该变量可引用具有与委托相同的签名的任何方法。You can use the delegate type to declare a variable that can refer to any method with the same signature as the delegate.

事件处理程序委托的标准签名定义不返回值的方法。The standard signature of an event handler delegate defines a method that does not return a value. 此方法的第一个参数的类型Object为, 并引用引发事件的实例。This method's first parameter is of type Object and refers to the instance that raises the event. 它的第二个参数从EventArgs类型派生, 并保存事件数据。Its second parameter is derived from type EventArgs and holds the event data. 如果事件不生成事件数据, 第二个参数就是EventArgs.Empty字段的值。If the event does not generate event data, the second parameter is simply the value of the EventArgs.Empty field. 否则, 第二个参数是从EventArgs派生的类型, 提供保存事件数据所需的任何字段或属性。Otherwise, the second parameter is a type derived from EventArgs and supplies any fields or properties needed to hold the event data.

EventHandler委托是一个预定义的委托, 专门表示不生成数据的事件的事件处理程序方法。The EventHandler delegate is a predefined delegate that specifically represents an event handler method for an event that does not generate data. 如果事件确实生成了数据, 则必须使用泛型EventHandler<TEventArgs>委托类。If your event does generate data, you must use the generic EventHandler<TEventArgs> delegate class.

若要将事件与将处理事件的方法相关联, 请将委托的实例添加到事件。To associate the event with the method that will handle the event, add an instance of the delegate to the event. 除非移除了该委托,否则每当发生该事件时就会调用事件处理程序。The event handler is called whenever the event occurs, unless you remove the delegate.

有关事件处理程序委托的详细信息, 请参阅处理和引发事件For more information about event handler delegates, see Handling and Raising Events.

扩展方法

GetMethodInfo(Delegate) GetMethodInfo(Delegate) GetMethodInfo(Delegate) GetMethodInfo(Delegate)

获取指示指定委托表示的方法的对象。Gets an object that represents the method represented by the specified delegate.

适用于

另请参阅