定義 Windows Form 控制項中的事件
如需定義自訂事件的詳細資訊，請參閱引發事件。 如果您定義不含任何關聯資料的事件，請使用事件資料的基底型別 (Base Type) EventArgs，並使用 EventHandler 做為事件委派 (Delegate)。 剩下要做的事就是定義事件成員和引發事件的保護的 OnEventName 方法。
下列程式碼片段示範 FlashTrackBar 自訂控制項如何定義自訂事件 ValueChanged。 如需 FlashTrackBar 範例的完整程式碼，請參閱 HOW TO：建立顯示進度的 Windows Form 控制項。
Option Explicit
Option Strict
Imports System
Imports System.Windows.Forms
Imports System.Drawing
Public Class FlashTrackBar
Inherits Control
' The event does not have any data, so EventHandler is adequate
' as the event delegate.
' Define the event member using the event keyword.
' In this case, for efficiency, the event is defined
' using the event property construct.
Public Event ValueChanged As EventHandler
' The protected method that raises the ValueChanged
' event when the value has actually
' changed. Derived controls can override this method.
Protected Overridable Sub OnValueChanged(e As EventArgs)
RaiseEvent ValueChanged(Me, e)
End Sub
End Class
using System;
using System.Windows.Forms;
using System.Drawing;
public class FlashTrackBar : Control {
// The event does not have any data, so EventHandler is adequate
// as the event delegate.
private EventHandler onValueChanged;
// Define the event member using the event keyword.
// In this case, for efficiency, the event is defined
// using the event property construct.
public event EventHandler ValueChanged {
add {
onValueChanged += value;
}
remove {
onValueChanged -= value;
}
}
// The protected method that raises the ValueChanged
// event when the value has actually
// changed. Derived controls can override this method.
protected virtual void OnValueChanged(EventArgs e) {
if (ValueChanged != null) {
ValueChanged(this, e);
}
}
}