How to run VBA code when cell contents are changed via formula - excel

Question

The code below works fine when I manually update column I. What I need is to know if there is a way to still have this code work when I have column I updated by a formula.
Private Sub Worksheet_Change(ByVal Target As Excel.Range)
With Target
If .Count > 1 Then Exit Sub
If Not Intersect(Range("I3:I30"), .Cells) Is Nothing Then
Application.EnableEvents = False
If IsEmpty(.Value) Then
.Offset(0, -1).ClearContents
Else
With .Offset(0, -1)
.NumberFormat = "m/d/yy h:mm"
.Value = Now
End With
End If
Application.EnableEvents = True
End If
End With
End Sub

Answer 1

Worksheet_Change does not fire in responce to a formula update.
See Excel help for Worksheet_Change
Occurs when cells on the worksheet are changed by the user or by an external link.
You could maybe achieve what you want with the Worksheet_Calculate event.
Assuming you want to put a time stamp next to the cells when those vall values change, try this (in addition to your Change event).
Note the use of the Static variable to track previous values, since Calculate event does nopt provide a Target parameter like Change does. This method may not be robust enough since Static's get reset if you break vba execution (eg on an unhandled error). If you want it more robust, consider saving previous values on another (hidden) sheet.
Private Sub Worksheet_Calculate()
Dim rng As Range, cl As Range
Static OldData As Variant
Application.EnableEvents = False
Set rng = Me.Range("I3:I30")
If IsEmpty(OldData) Then
OldData = rng.Value
End If
For Each cl In rng.Cells
If Len(cl) = 0 Then
cl.Offset(0, -1).ClearContents
Else
If cl.Value <> OldData(cl.Row - rng.Row + 1, 1) Then
With cl.Offset(0, -1)
.NumberFormat = "m/d/yy h:mm:ss"
.Value = Now
End With
End If
End If
Next
OldData = rng.Value
Application.EnableEvents = True
End Sub
Update
Tested routine on sample sheet, all works as expected
Sample file contains the same code repeated on 25 sheets, and range to time stamp is 10000 rows long.
To avoid repeating the code, use the Workbook_ events. To minimise run time use variant arrays for the loop.
Private Sub Workbook_SheetCalculate(ByVal Sh As Object)
Dim rng As Range
Dim NewData As Variant
Dim i As Long
Static OldData As Variant
Application.EnableEvents = False
Set rng = Sh.Range("B2:C10000") ' <-- notice range includes date column
NewData = rng
If IsEmpty(OldData) Then
OldData = rng.Value
End If
For i = LBound(NewData, 1) To UBound(NewData, 1)
If Len(NewData(i, 1)) = 0 And Len(NewData(i, 2)) > 0 Then
rng.Cells(i, 2).ClearContents
Else
If NewData(i, 1) <> OldData(i, 1) Then
With rng.Cells(i, 2)
.NumberFormat = "m/d/yy -- h:mm:ss"
.Value = Now
End With
End If
End If
Next
OldData = rng.Value
Application.EnableEvents = True
End Sub
Private Sub Workbook_SheetChange(ByVal Sh As Object, ByVal Target As Range)
'Activate date population on cell change
With Target
If .Count > 1 Then Exit Sub
If Not Intersect(Sh.Range("B2:B10000"), .Cells) Is Nothing Then
Application.EnableEvents = False
If IsEmpty(.Value) Then
.Offset(0, 1).ClearContents
Else
'Populate date and time in column c
With .Offset(0, 1)
.NumberFormat = "mm/dd/yyyy -- hh:mm:ss"
.Value = Now
End With
End If
Application.EnableEvents = True
End If
End With
End Sub