Question

I have an event handler which handles its event just fine. However, I don’t want to be able to call the handler directly or, more specifically, give my fellow programmers the ability to call it directly, since I want to update nudCurrent.Value only when the laser current is set.

Public Class TestClass

    Dim WithEvents myCurrentSource As New CurrentSourceClass

    Private Sub TestScript()
        'among other things, sets current to 85
        myCurrentSource.SetCurrent(85)
    End Sub

    Private Sub handleLaserCurrentSet() Handles myCurrentSource.LaserCurrentSet
        Me.nudCurrent.Value = myCurrentSource.GetCurrent()
    End Sub

End Class

Public Class CurrentSourceClass

    Public Event LaserCurrentSet()

    Private currentSet As Double = Double.NaN

    Public Sub SetCurrent(ByVal dCurrentAmps As Double)
        ' set the current on the current source here
        Me.currentSet = dCurrentAmps
        ' then raise the event
        RaiseEvent LaserCurrentSet()
    End Sub

    Public Function GetCurrent() As Double
        Return Me.currentSet
    End Function

End Class

I can’t think of a way to restrict the access to the event handler routine within its scope, so I’m looking for an alternate way of doing this. What is the best practice?

*I understand that I could just put me.nudCurrent.Value = 85 after setting the current, but I like the neatness of the event driven UI updates. Can I have my cake and eat it too?

Answer 1

You can use an anonymous event handler

AddHandler myCurrentSource.LaserCurrentSet,
                Sub()
                    Me.nudCurrent.Value = myCurrentSource.GetCurrent()
                End Sub

But keep in mind that the value can be set from anywhere inside the class. You cannot restrict that.