c# 用户控件添加事件

  如何：在类中实现事件

下面的过程说明如何在类中实现事件。第一个过程实现没有关联数据的事件，它将 System ..::.EventArgs 类和 System ..::.EventHandler 类用作事件数据和委托处理程序。第二个过程实现具有自定义数据的事件，它为事件数据和事件委托处理程序定义自定义类。

有关阐释引发和处理事件的完整示例，请参见 如何：引发和使用事件 。

实现不具有事件特定的数据的事件

1. 在类中定义公共事件成员。将事件成员的类型设置为 System ..::.EventHandler 委托。

   C#	复制代码
   public class Countdown { ... public event EventHandler CountdownCompleted; }

   Visual Basic	复制代码
   Public Class Countdown ... Public Event CountdownCompleted As EventHandler End Class

2. 在引发事件的类中提供一个受保护的方法。对 OnEventName 方法进行命名。在该方法中引发该事件。

   C#	复制代码
   public class Countdown { ... public event EventHandler CountdownCompleted; protected virtual void OnCountdownCompleted(EventArgs e) { if (CountdownCompleted != null) CountdownCompleted(this, e); } }

   Visual Basic	复制代码
   Public Class Countdown ... Public Event CountdownCompleted As EventHandler Protected Overridable Sub OnCountdownCompleted(e As EventArgs) RaiseEvent CountdownCompleted(Me, e) End Sub End Class

3. 在类中确定引发该事件的时间。调用 OnEventName 以引发该事件。

   C#	复制代码
   public class Countdown { ... public void Decrement { internalCounter = internalCounter - 1; if (internalCounter == 0) OnCountdownCompleted(new EventArgs()); } }

   Visual Basic	复制代码
   Public Class Countdown ... Public Function Decrement InternalCounter = internalCounter - 1 If internalCounter = 0 OnCountdownComplete(New EventArgs()) End If End Function End Class

实现具有事件特定的数据的事件

1. 定义一个提供事件数据的类。对类 EventNameArgs 进行命名，从 System ..::.EventArgs 派生该类，然后添加所有事件特定的成员。

   C#	复制代码
   public class AlarmEventArgs : EventArgs { private readonly int nrings = 0; private readonly bool snoozePressed = false; //Constructor. public AlarmEventArgs(bool snoozePressed, int nrings) { this.snoozePressed = snoozePressed; this.nrings = nrings; } //Properties. public string AlarmText { ... } public int NumRings { ... } public bool SnoozePressed{ ... } }

   Visual Basic

   复制代码

   Public Class AlarmEventArgs Inherits EventArgs Private nrings As Integer = 0 Private _snoozePressed As Boolean = False 'Constructor. Public Sub New(ByVal snoozePressed As Boolean, ByVal nrings As Integer) Me.snoozePressed = snoozePressed Me.nrings = nrings End Sub 'Properties. Public ReadOnly Property AlarmText() As String ... End Property Public ReadOnly Property NumRings() As Integer ... End Property Public ReadOnly Property SnoozePressed() As Boolean ... End Property End Class

2. 声明事件的委托。对委托 EventNameEventHandler 进行命名。

   C#	复制代码
   public delegate void AlarmEventHandler(object sender, AlarmEventArgs e);

   Visual Basic	复制代码
   Public Delegate Sub AlarmEventHandler(sender As Object, e As AlarmEventArgs)

3. 在类中定义名为 EventName 的公共事件成员。将事件成员的类型设置为事件委托类型。

   C#	复制代码
   public class AlarmClock { ... public event AlarmEventHandler Alarm; }

   Visual Basic	复制代码
   Public Class AlarmClock ... Public Event Alarm As AlarmEventHandler End Class

4. 在引发事件的类中定义一个受保护的方法。对 OnEventName 方法进行命名。在该方法中引发该事件。

   C#	复制代码
   public class AlarmClock { ... public event AlarmHandler Alarm; protected virtual void OnAlarm(AlarmEventArgs e) { if (Alarm != null) Alarm(this, e); } }

   Visual Basic	复制代码
   Public Class AlarmClock ... Public Event Alarm As AlarmEventHandler Protected Overridable Sub OnAlarm(e As AlarmEventArgs) RaiseEvent Alarm(Me, e) End Sub End Class

5. 在类中确定引发该事件的时间。调用 OnEventName 以引发该事件并使用 EventNameEventArgs 传入事件特定的数据。

   C#	复制代码
   Public Class AlarmClock { ... public void Start() { ... System.Threading.Thread.Sleep(300); AlarmEventArgs e = new AlarmEventArgs(false, 0); OnAlarm(e); } }

   Visual Basic	复制代码
   Public Class AlarmClock ... Public Function Start ... System.Threading.Thread.Sleep(300) Dim e As AlarmEventArgs = New AlarmEventArgs(False, 0) OnAlarm(e) End Function End Class