Calling OnTime method in a Custom Class - vba

Question

I'm trying to use the .OnTime method in a class module, but can't figure out how to call a procedure in the class. All of the .OnTime examples I've seen refer to using the method from a standard code module rather than a custom class. Is there any way of calling a procedure in the class module rather than a standard code module?
#Alex P: Updated to include code. Here is the Class Module:
Option Explicit
Public Sub Test()
MsgBox "Success"
End Sub
Private Sub Class_Initialize()
Application.OnTime EarliestTime:=Now + TimeValue("00:00:03"), _
Procedure:="Test"
End Sub
And the Standard Module:
Option Explicit
Public Sub TestOnTime()
Dim OnTime As CCOnTime
Set OnTime = New CCOnTime
End Sub
I've also tried Procedure:="CClass.Test"

Answer 1

You can do it, but the call-back needs to be bounced back into the object from a Standard Module or a Worksheet Module or Thisworkbook.
Here is an example that pulses a value in a worksheet cell.
The timer is (almost) encapsulated in the cOnTime Class.
A cOnTime Object is instantiated in the host worksheet, whose code module can have a property to set the pulse time as well as the call-back routine.
If you protect the sheet, it will start pulsing and you can stop it by un-protecting the sheet.
If you navigate away from the host sheet, the timer is killed and if you navigate back it re-starts (as long as the sheet is protected).
Class cOnTime
Option Explicit
Const DEFPulseTime = "PulseTime"
Const DEFearliestTime As Long = 5
Const DEFlatestTime As Long = 15
Public WithEvents wb As Workbook
Public ws As Worksheet
Private DoWhen As String
Public mPulseTime As Long
Public mNextTime As Double
Property Let callBackDoWhen(cb As String)
DoWhen = "'" & wb.Name & "'!" & ws.CodeName & "." & cb 'e.g. 'wb Name.xlsm'!Sheet1.kickdog
End Property
Private Function PulseTime() As Long
On Error Resume Next
PulseTime = CallByName(ws, DEFPulseTime, VbGet)
If Err.number <> 0 Then
PulseTime = DEFearliestTime
End If
On Error GoTo 0
End Function
Property Get designMode() As Boolean
designMode = Not ws.ProtectContents
End Property
Public Sub kickDog()
Const myName As String = "kickDog"
Dim psMessage As String
If ws Is ActiveSheet And Not designMode Then
mNextTime = Now + TimeSerial(0, 0, mPulseTime)
On Error Resume Next
Application.OnTime mNextTime, DoWhen
On Error GoTo 0
End If
Exit Sub
End Sub
Public Sub killDog()
If ws Is Nothing Or mNextTime = 0 Then Exit Sub
On Error Resume Next
Application.OnTime mNextTime, DoWhen, , False
On Error GoTo 0
End Sub
Private Sub Class_Initialize()
Dim errorContext As String
On Error GoTo enableAndExit
Set wb = ActiveWorkbook
Set ws = ActiveSheet
On Error GoTo 0
callBackDoWhen = DEFDoWhen
callBackPulseTime = DEFPulseTime
mPulseTime = PulseTime
kickDog
Exit Sub
enableAndExit:
If Err <> 0 Then
If ws Is Nothing Then
errorContext = "ws"
ElseIf wb Is Nothing Then
errorContext = "wb"
End If
End If
End Sub
Private Sub Class_Terminate()
Const myName As String = "Class_Terminate"
On Error Resume Next
killDog
Set ws = Nothing
Set wb = Nothing
Exit Sub
End Sub
Private Sub wb_WindowActivate(ByVal Wn As Window)
wb_Open
End Sub
Private Sub wb_WindowDeactivate(ByVal Wn As Window)
killDog
End Sub
Private Sub wb_BeforeClose(Cancel As Boolean)
killDog
End Sub
Private Sub wb_BeforeSave(ByVal SaveAsUI As Boolean, Cancel As Boolean)
If SaveAsUI Then killDog
End Sub
In Worksheet Module
Option Explicit
Const cPulseTime As Long = 1
Dim mOnTime As cOnTime
Property Get PulseTime() As Long
PulseTime = cPulseTime
End Property
'****************************************
'Timer call-back for cOnTime
Public Sub kickDog()
' Code to execute on timer event
'******************************************
On Error Resume Next
Me.Cells(1, 1) = Not Me.Cells(1, 1)
On Error GoTo 0
'******************************************
Debug.Print "woof!!"
mOnTime.kickDog
End Sub
Private Sub Worksheet_Activate()
Me.Cells(1,1) = False
Set mOnTime = New cOnTime
End Sub
Private Sub Worksheet_Deactivate()
On Error Resume Next
Set mOnTime = Nothing
End Sub

Answer 2

You are asking for magic - VBA is a comprehensive tool but it is not magic.
The reason is that every Class module is simply a template which can be instantiated any number of times in the application code. Excel could not hope to correctly guess which particular instantiation of the Class module is the correct one on which to invoke the method. You are responsible for making this decision and managing the references to the appropriate Class instance.
Ah you say - But there is no private data/references being used by the method I want called. It is a static method. Well the answer to that is that VBA does not support static methods on Class modules, only on Standard modules. Any method that you wish to declare to the environment as being static is declared as being static by being included in a standard module.
So, place your call-back method in a Standard module, and declare a private member that holds a reference to the particular instance of the Class that you wish to handle the event.

Answer 3

One alternative route which isn't specified by others here but, I think, would theoretically work is:
Register VBA object as an active object with a specified GUID
Launch a PowerShell (or binary) daemon to connect to the object with specified GUID and call a specified method on that object every n seconds.
Pros:
Totally encapsulated
Cons:
Launches external process
Method likely has to be public (unless connection points can be abused)
Potentially crash-prone
I haven't implemented such a solution yet but intend to on stdCOM of stdVBA library if everything works out.