在 Windows 窗体控件中定义事件
有关定义自定义事件的详细信息，请参见 引发事件。 如果您定义的事件没有任何关联的数据，则使用事件数据的基类型 EventArgs，并使用 EventHandler 作为事件委托。 剩下的工作就是定义一个事件成员和一个引发该事件的受保护的 On事件名称 方法。
以下代码片段说明了 FlashTrackBar 自定义控件如何定义自定义事件 ValueChanged。 有关 FlashTrackBar 示例的完整代码，请参见 如何：创建显示进度的 Windows 窗体控件。
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);
}
}
}