Creating A Custom Event With VBA - vba

Question

I'm trying struggling to understand how to create a custom event using class modules in VBA.
I've put together the simple following example. You put a value in A1 and B1 and then re activate the sheet to calculate the sum of the two and then I hoped an event would fire to warn of calculation, but nothing happens.
I'd be very grateful for any help solving this example.
Class module cCalc:
Dim m_wks As Worksheet
Public Event BeforeCalc()
Property Set Worksheet(wks As Worksheet)
Set m_wks = wks
End Property
Public Sub Calc()
Dim dVal1 As Double
Dim dVal2 As Double
With m_wks
dVal1 = .Range("A1").Value
dVal2 = .Range("B1").Value
RaiseEvent BeforeCalc
.Range("C1").Value = dVal1 + dVal2
End With
End Sub
In a module mGlobal:
Public gCalc As cCalc
In the code behind Sheet1:
Private WithEvents calcEvent As cCalc
Private Sub calcEvent_BeforeCalc()
MsgBox "About to Calc!", vbInformation
End Sub
Private Sub Worksheet_Activate()
Set gCalc = New cCalc
Set gCalc.Worksheet = ActiveSheet
gCalc.Calc
End Sub

Answer 1

You can't declare event-driven classes in modules. You'll need to set the cCalc reference in gModule equal to the object you declared WithEvents in Sheet1. Change your code in Sheet1 to what i wrote below and it will work:
Private WithEvents calcEvent As cCalc
Private Sub calcEvent_BeforeCalc()
MsgBox "About to Calc!", vbInformation
End Sub
Private Sub Worksheet_Activate()
Set calcEvent = New cCalc 'Instantiate the WithEvents object above
Set mGlobal.gCalc = calcEvent 'Set the object declared in gModule
Set mGlobal.gCalc.Worksheet = ActiveSheet
mGlobal.gCalc.Calc
End Sub
Note that this is using the variable you put in gModule... The event that is actually called is still calcEvent_BeforeCalc(), which is good as this way you can have n number of objects defined in gModule that would all fire off the same event code when the event is triggered.
To simplify the code, you could always just write:
Private Sub Worksheet_Activate()
Set calcEvent = New cCalc
Set calcEvent.Worksheet = ActiveSheet
calcEvent.Calc
End Sub