How to detect changes in cell format?

Question

I want to embed a procedure in an Excel sheet that will detect when a cell's format changes, e.g. from Text to Number.

But I can't figure out how to get the cell's format type. I tried using the Worksheet_Change event handler to check the data type, as follows:

Private Sub worksheet_change(ByVal Target As Range)

If Target.Address = "a1" Then
    If VarType(Target) <> 5 Then
        MsgBox "cell format has been changed"
    End If
End If


End Sub

But with this code in place, if I change cell A1's data type from Number to Text, Worksheet_Change is not triggered; the event handler is only called if I change the contents of the cell.

Also, this procedure can detect if the contents are changed from a number to an alphabetical string, e.g. from "35.12" to "abcd", but not Number-type number to Text-type number; if I set cell B1 to text, then enter "40", then paste the contents of cell B1 into cell A1, vartype() still returns "5", so the alert is not triggered.

How can I detect that the format has changed, regardless of whether the content type has changed?

Answer 1

Great question!

If you are only looking to trigger an event on the NumberFormat change (you appear to be calling this incorrectly the data format, NumberFormat is the attribute you want), the following is a good example.

I'm intercepting all selection change events and checking if any NumberFormat changed.

Option Explicit

'keep track of the previous
Public m_numberFormatDictionary As New dictionary
Public m_previousRange As Range

Private Sub Worksheet_SelectionChange(ByVal Target As Range)

    'requires reference to Microsoft Scripting Runtime

    Dim c As Variant
    Dim wasChange As Boolean


    Debug.Print "***********************"

    'make sure you had a previous selection and it was initialized
    If m_numberFormatDictionary.Count > 0 And Not m_previousRange Is Nothing Then

        'Iterate through all your previous formattings and see if they are the same
        For Each c In m_previousRange
            Debug.Print "Found " & c.NumberFormat & " in " & c.Address
            Debug.Print "Stored value is " & m_numberFormatDictionary(c.Address) & " in " & c.Address

            'print out when they are different
            If c.NumberFormat <> m_numberFormatDictionary(c.Address) Then
                Debug.Print "~~~~~~ Different ~~~~~~"
                wasChange = True
            End If

        Next c
    End If

    'clear previous values
    m_numberFormatDictionary.RemoveAll

    'Make sure you don't error out Excel by checking a million things
    If Target.Cells.Count < 1000 Then

        'Add each cell format back into the previous formatting
        For Each c In Target
            Debug.Print "Adding " & c.NumberFormat & " to " & c.Address
            m_numberFormatDictionary.Add c.Address, c.NumberFormat
        Next c

        'reset the range to what you just selected
        Set m_previousRange = Target
    End If

    'simple prompt now, not sure what your use case is
    If wasChange Then
        MsgBox "There was at least one change!"
    End If

End Sub

I'm not exactly sure what you are looking for, you'll have to modify the print/msgbox statements appropriately. Depending on your use case you may have to modify this slightly but it works in all my test examples.