EventHandler<TEventArgs> 代理人

定義

命名空間:

System

組件:

System.Runtime.dll

代表這個事件提供資料時將處理事件的方法。

generic <typename TEventArgs>
public delegate void EventHandler(System::Object ^ sender, TEventArgs e);

public delegate void EventHandler<TEventArgs>(object? sender, TEventArgs e);

type EventHandler<'EventArgs> = delegate of obj * 'EventArgs -> unit

Public Delegate Sub EventHandler(Of TEventArgs)(sender As Object, e As TEventArgs)

類型參數

TEventArgs

該事件所產生事件資料的類型。

參數

sender

Object

事件的來源。

e

TEventArgs

包含事件資料的物件。

範例

下列範例顯示名為 ThresholdReached 的事件。 事件與 EventHandler<TEventArgs> 委派相關聯。

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; }
    }
}

open System

type ThresholdReachedEventArgs(threshold, timeReached) =
    inherit EventArgs()
    member _.Threshold = threshold
    member _.TimeReached = timeReached

type Counter(threshold) =
    let mutable total = 0

    let thresholdReached = Event<_>()

    member this.Add(x) =
        total <- total + x
        if total >= threshold then
            let args = ThresholdReachedEventArgs(threshold, DateTime.Now)
            thresholdReached.Trigger(this, args)

    [<CLIEvent>]
    member _.ThresholdReached = thresholdReached.Publish

let c_ThresholdReached(sender, e: ThresholdReachedEventArgs) =
    printfn $"The threshold of {e.Threshold} was reached at {e.TimeReached}."
    exit 0

let c = Counter(Random().Next 10)
c.ThresholdReached.Add c_ThresholdReached

printfn "press 'a' key to increase total"
while Console.ReadKey(true).KeyChar = 'a' do
    printfn "adding one"
    c.Add 1

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

備註

.NET Framework中的事件模型是以事件委派為基礎，該委派會與其處理常式連接事件。 若要引發事件，需要兩個元素：

• 委派，參考提供事件回應的方法。

• 選擇性地，如果事件提供資料，則為保存事件資料的類別。

委派是定義簽章的類型，也就是方法的傳回數值型別和參數清單類型。 您可以使用委派類型來宣告變數，該變數可以參考與委派相同的簽章的任何方法。

事件處理常式委派的標準簽章會定義不會傳回值的方法。 這個方法的第一個參數的類型為 ， Object 並參考引發事件的實例。 其第二個參數衍生自 類型 EventArgs ，並保存事件資料。 如果事件不會產生事件資料，則第二個參數只是欄位的值 EventArgs.Empty 。 否則，第二個參數是衍生自 EventArgs 的類型，並提供保存事件資料所需的任何欄位或屬性。

委派 EventHandler<TEventArgs> 是預先定義的委派，代表產生資料之事件的事件處理常式方法。 使用 EventHandler<TEventArgs> 的優點是，如果您的事件產生事件資料，您不需要撰寫自己的自訂委派程式碼。 您只需提供事件資料物件的型別做為泛型參數。

若要將事件與將處理事件的方法產生關聯，請將委派的實例新增至 事件。 除非您移除委派，否則每當事件發生時就會呼叫事件處理常式。

如需事件處理常式委派的詳細資訊，請參閱 處理和引發事件。

擴充方法

GetMethodInfo(Delegate)

取得表示特定委派所代表之方法的物件。

另請參閱

• EventHandler
• EventArgs
• Delegate
• 處理和引發事件
• 如何：引發和使用事件
• 事件 (Visual Basic)
• 事件 (C# 程式設計手冊)
• 事件 (F#)
• 事件和路由事件概觀 (Windows 市集應用程式)