如何：引发和使用事件
更新：2007 年 11 月
下面的示例程序阐释如何在一个类中引发一个事件，然后在另一个类中处理该事件。 AlarmClock 类定义公共事件 Alarm，并提供引发该事件的方法。 AlarmEventArgs 类派生自 EventArgs，并定义 Alarm 事件特定的数据。 WakeMeUp 类定义处理 Alarm 事件的 AlarmRang 方法。 AlarmDriver 类一起使用类，将使用 WakeMeUp 的 AlarmRang 方法设置为处理 AlarmClock 的 Alarm 事件。
示例
// EventSample.cs.
//
namespace EventSample
{
using System;
using System.ComponentModel;
// Class that contains the data for
// the alarm event. Derives from System.EventArgs.
//
public class AlarmEventArgs : EventArgs
{
private readonly bool snoozePressed ;
private readonly int nrings;
//Constructor.
//
public AlarmEventArgs(bool snoozePressed, int nrings)
{
this.snoozePressed = snoozePressed;
this.nrings = nrings;
}
// The NumRings property returns the number of rings
// that the alarm clock has sounded when the alarm event
// is generated.
//
public int NumRings
{
get { return nrings;}
}
// The SnoozePressed property indicates whether the snooze
// button is pressed on the alarm when the alarm event is generated.
//
public bool SnoozePressed
{
get {return snoozePressed;}
}
// The AlarmText property that contains the wake-up message.
//
public string AlarmText
{
get
{
if (snoozePressed)
{
return ("Wake Up!!! Snooze time is over.");
}
else
{
return ("Wake Up!");
}
}
}
}
// Delegate declaration.
//
public delegate void AlarmEventHandler(object sender, AlarmEventArgs e);
// The Alarm class that raises the alarm event.
//
public class AlarmClock
{
private bool snoozePressed = false;
private int nrings = 0;
private bool stop = false;
// The Stop property indicates whether the
// alarm should be turned off.
//
public bool Stop
{
get {return stop;}
set {stop = value;}
}
// The SnoozePressed property indicates whether the snooze
// button is pressed on the alarm when the alarm event is generated.
//
public bool SnoozePressed
{
get {return snoozePressed;}
set {snoozePressed = value;}
}
// The event member that is of type AlarmEventHandler.
//
public event AlarmEventHandler Alarm;
// The protected OnAlarm method raises the event by invoking
// the delegates. The sender is always this, the current instance
// of the class.
//
protected virtual void OnAlarm(AlarmEventArgs e)
{
AlarmEventHandler handler = Alarm;
if (handler != null)
{
// Invokes the delegates.
handler(this, e);
}
}
// This alarm clock does not have
// a user interface.
// To simulate the alarm mechanism it has a loop
// that raises the alarm event at every iteration
// with a time delay of 300 milliseconds,
// if snooze is not pressed. If snooze is pressed,
// the time delay is 1000 milliseconds.
//
public void Start()
{
for (;;)
{
nrings++;
if (stop)
{
break;
}
else if (snoozePressed)
{
System.Threading.Thread.Sleep(1000);
{
AlarmEventArgs e = new AlarmEventArgs(snoozePressed,
nrings);
OnAlarm(e);
}
}
else
{
System.Threading.Thread.Sleep(300);
AlarmEventArgs e = new AlarmEventArgs(snoozePressed,
nrings);
OnAlarm(e);
}
}
}
}
// The WakeMeUp class has a method AlarmRang that handles the
// alarm event.
//
public class WakeMeUp
{
public void AlarmRang(object sender, AlarmEventArgs e)
{
Console.WriteLine(e.AlarmText +"\n");
if (!(e.SnoozePressed))
{
if (e.NumRings % 10 == 0)
{
Console.WriteLine(" Let alarm ring? Enter Y");
Console.WriteLine(" Press Snooze? Enter N");
Console.WriteLine(" Stop Alarm? Enter Q");
String input = Console.ReadLine();
if (input.Equals("Y") ||input.Equals("y")) return;
else if (input.Equals("N") || input.Equals("n"))
{
((AlarmClock)sender).SnoozePressed = true;
return;
}
else
{
((AlarmClock)sender).Stop = true;
return;
}
}
}
else
{
Console.WriteLine(" Let alarm ring? Enter Y");
Console.WriteLine(" Stop Alarm? Enter Q");
String input = Console.ReadLine();
if (input.Equals("Y") || input.Equals("y")) return;
else
{
((AlarmClock)sender).Stop = true;
return;
}
}
}
}
// The driver class that hooks up the event handling method of
// WakeMeUp to the alarm event of an Alarm object using a delegate.
// In a forms-based application, the driver class is the
// form.
//
public class AlarmDriver
{
public static void Main (string[] args)
{
// Instantiates the event receiver.
WakeMeUp w= new WakeMeUp();
// Instantiates the event source.
AlarmClock clock = new AlarmClock();
// Wires the AlarmRang method to the Alarm event.
clock.Alarm += new AlarmEventHandler(w.AlarmRang);
clock.Start();
}
}
}
' EventSample.vb.
'
Option Explicit
Option Strict
Imports System
Imports System.ComponentModel
Imports Microsoft.VisualBasic
Namespace EventSample
' Class that contains the data for
' the alarm event. Derives from System.EventArgs.
'
Public Class AlarmEventArgs
Inherits EventArgs
Private _snoozePressed As Boolean
Private nrings As Integer
'Constructor.
'
Public Sub New(snoozePressed As Boolean, nrings As Integer)
Me._snoozePressed = snoozePressed
Me.nrings = nrings
End Sub
' The NumRings property returns the number of rings
' that the alarm clock has sounded when the alarm event
' is generated.
'
Public ReadOnly Property NumRings() As Integer
Get
Return nrings
End Get
End Property
' The SnoozePressed property indicates whether the snooze
' button is pressed on the alarm when the alarm event is generated.
'
Public ReadOnly Property SnoozePressed() As Boolean
Get
Return _snoozePressed
End Get
End Property
' The AlarmText property that contains the wake-up message.
'
Public ReadOnly Property AlarmText() As String
Get
If _snoozePressed Then
Return "Wake Up!!! Snooze time is over."
Else
Return "Wake Up!"
End If
End Get
End Property
End Class
' Delegate declaration.
'
Public Delegate Sub AlarmEventHandler(sender As Object, _
e As AlarmEventArgs)
' The Alarm class that raises the alarm event.
'
Public Class AlarmClock
Private _snoozePressed As Boolean = False
Private nrings As Integer = 0
Private stopFlag As Boolean = False
' The Stop property indicates whether the
' alarm should be turned off.
'
Public Property [Stop]() As Boolean
Get
Return stopFlag
End Get
Set
stopFlag = value
End Set
End Property
' The SnoozePressed property indicates whether the snooze
' button is pressed on the alarm when the alarm event is generated.
'
Public Property SnoozePressed() As Boolean
Get
Return _snoozePressed
End Get
Set
_snoozePressed = value
End Set
End Property
' The event member that is of type AlarmEventHandler.
'
Public Event Alarm As AlarmEventHandler
' The protected OnAlarm method raises the event by invoking
' the delegates. The sender is always this, the current instance
' of the class.
'
Protected Overridable Sub OnAlarm(e As AlarmEventArgs)
RaiseEvent Alarm(Me, e)
End Sub
' This alarm clock does not have
' a user interface.
' To simulate the alarm mechanism it has a loop
' that raises the alarm event at every iteration
' with a time delay of 300 milliseconds,
' if snooze is not pressed. If snooze is pressed,
' the time delay is 1000 milliseconds.
'
Public Sub Start()
Do
nrings += 1
If stopFlag Then
Exit Do
Else
If _snoozePressed Then
System.Threading.Thread.Sleep(1000)
If (True) Then
Dim e As New AlarmEventArgs(_snoozePressed, nrings)
OnAlarm(e)
End If
Else
System.Threading.Thread.Sleep(300)
Dim e As New AlarmEventArgs(_snoozePressed, nrings)
OnAlarm(e)
End If
End If
Loop
End Sub
End Class
' The WakeMeUp class has a method AlarmRang that handles the
' alarm event.
'
Public Class WakeMeUp
Public Sub AlarmRang(sender As Object, e As AlarmEventArgs)
Console.WriteLine((e.AlarmText + ControlChars.Cr))
If Not e.SnoozePressed Then
If e.NumRings Mod 10 = 0 Then
Console.WriteLine(" Let alarm ring? Enter Y")
Console.WriteLine(" Press Snooze? Enter N")
Console.WriteLine(" Stop Alarm? Enter Q")
Dim input As String = Console.ReadLine()
If input.Equals("Y") Or input.Equals("y") Then
Return
Else
If input.Equals("N") Or input.Equals("n") Then
CType(sender, AlarmClock).SnoozePressed = True
Return
Else
CType(sender, AlarmClock).Stop = True
Return
End If
End If
End If
Else
Console.WriteLine(" Let alarm ring? Enter Y")
Console.WriteLine(" Stop Alarm? Enter Q")
Dim input As String = Console.ReadLine()
If input.Equals("Y") Or input.Equals("y") Then
Return
Else
CType(sender, AlarmClock).Stop = True
Return
End If
End If
End Sub
End Class
' The driver class that hooks up the event handling method of
' WakeMeUp to the alarm event of an Alarm object using a delegate.
' In a forms-based application, the driver class is the
' form.
'
Public Class AlarmDriver
Public Shared Sub Main()
' Instantiates the event receiver.
Dim w As New WakeMeUp()
' Instantiates the event source.
Dim clock As New AlarmClock()
' Wires the AlarmRang method to the Alarm event.
AddHandler clock.Alarm, AddressOf w.AlarmRang
clock.Start()
End Sub
End Class
End Namespace