How do you create a cancelable event in vb.net

event-handling, events, vb.net

Solution

You can re-use the System.ComponentModel.CancelEventArgs class in the .NET framework.

Public Event Announcing As EventHandler(Of AnnounceNavigateEventArgs)

Protected Sub OnAnnounce()
    Dim e As New AnnounceNavigateEventArgs

    RaiseEvent Announcing(Me, e)

    If Not e.Cancel Then
        ' announce
    End If
End Sub

Public Class AnnounceNavigateEventArgs
    Inherits System.ComponentModel.CancelEventArgs
End Class

Problem

IN VB.NET (not c#)... I want to create an event than can be canceled by the listener. Just like you can cancel the closing event of a winforms form in which case the form won't close. I have already implemented a derived class from EventArgs that has a settable Cancel property as follows: ``` Public Class AnnounceNavigateEventArgs Inherits EventArgs Private _cancel As Boolean = False ''' <summary> ''' Initializes a new instance of the AnnounceNavigateEventArgs class. ''' </summary> Public Sub New(ByRef cancel As Boolean) _cancel = cancel End Sub Public Property Cancel() As Boolean Get Return _cancel End Get Set(ByVal value As Boolean) _cancel = value End Set End Property End Class ``` Notice that I am passing the cancel argument byRef to the constructor. The listener I have setup is setting the property to Cancel=True. I thought ByRef meant that both _cancel and cancel would point to the same location on the stack and that setting _cancel=true would therefore make the cancel = true. But this is not the behavior I am getting. _cancel becomes true in the setter but I guess the argument to the constructor remains false. What is the proper way to do this in vb.net? Seth

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