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定義 Windows Form 控制項中的事件

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如需如何定義自訂事件的詳細資料，請參閱事件。 若定義的事件沒有任何相關聯的資料，請為事件資料使用基底類型 EventArgs，並以 EventHandler 做為事件委派。 接著就是定義事件成員及受保護的 OnEventName 方法 (引發事件用)。

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 樣本的完整程式碼，請參閱如何：建立可顯示進度的 Windows Forms 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)
   {  
       onValueChanged?.Invoke(this, e);  
   }  
}

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