Use regex to enforce cell validation? - regex

Question

Using Excel 2010. I want to only allow values in a cell that fit a given regex pattern. So I created a UDF module as follows:
Public re as RegExp
Public Function isValidRegex(rng As Range, pattern As String) As Boolean
If re Is Nothing Then
Set re = New RegExp
End If
re.pattern = pattern
isValidRegex = re.Test(rng.value)
End Function
I created a named range called THIS_CELL, so that the current cell can be passed to isValidRegex(), as follows:
=INDIRECT(ADDRESS(ROW(),COLUMN()))
I set a custom validation for the cell, using this formula:
=isValidRegex(THIS_CELL,"(my|regex)patt[ern]")
This generated the following error:
A named range you specified cannot be found.
According to this article, UDFs cannot be used in Custom validation formulas. The solution suggested in the article (putting the formula in another cell, making that cell into a named range, and referencing that cell in the Custom formula) won't work, because I need to be able to pass THIS_CELL as an argument to the function.
I also tried creating a named range called isValidRegexPattern, defining it as =isValidRegex(THIS_CELL,"(my|regex)patt[ern]"), and setting the Custom formula to =isValidRegexPattern, but this didn't work either; putting a breakpoint in isValidRegex() showed that the function wasn't even being called.
So, how can I use a UDF for cell validation?

Answer 1

You can use a static variable with the Worksheet_Change event to keep a snapshot of the prior values
The code below tracks the values in A1:A10 and uses a Regexp like yours to reject any non-numeric entries
The example below tries top copy and paste B1:B10 over A1:A10, only A6and A8 are allowed as they are numeric
to set the range initially change a cell outside the range of interest to trigger If IsEmpty(X) Then X = [a1:a10].Value2
change event
Private Sub Worksheet_Change(ByVal Target As Range)
Static X As Variant
Dim rng2 As Range
Dim rng3 As Range
If IsEmpty(X) Then X = [a1:a10].Value2
Set rng2 = Intersect([a1:a10], Target)
If rng2 Is Nothing Then Exit Sub
Application.EnableEvents = False
For Each rng3 In rng2
If Not isValidRegex(rng3, "\d+") Then rng3.Value = X(rng3.Row, 1)
Next
Application.EnableEvents = True
X = [a1:a10].Value2
End Sub
regexp
Function isValidRegex(rng As Range, pattern As String) As Boolean
Dim re As Object
Set re = CreateObject("vbscript.regexp")
re.pattern = pattern
isValidRegex = re.Test(rng.Value)
End Function

Answer 2

You seem to be reluctant to move over to a WorksheetChange event macro because you believe it does not 'capture the pre-change state of the cell'. That may be correct in the strictest definition but that doesn't mean you cannot capture the changed state, undo the change, determine whether the change is valid and only re-apply the change if it meets criteria.
I'm not going to produce a full regex validating function. This simply tests if the number typed into column E is less than zero or blank. If not then the cell reverts to its prechange state.
Private Sub Worksheet_Change(ByVal Target As Range)
If Target.Count > 1 Then Exit Sub
If Not Intersect(Target, Columns(5)) Is Nothing Then
If Not IsEmpty(Target) Then
On Error GoTo Safe_Exit
Application.EnableEvents = False
Dim vNEW As Variant
vNEW = Target.Value
Application.Undo
If bIs_It_Valid(vNEW) Then
Target = vNEW
Else
' put stuff like idiot warnings here
End If
End If
End If
Safe_Exit:
Application.EnableEvents = True
End Sub
Private Function bIs_It_Valid(val As Variant) As Boolean
If IsNumeric(val) Then _
bIs_It_Valid = CBool(val < 0)
Debug.Print bIs_It_Valid
End Function
That Worksheet_Change could probably be adjusted to work on a range of cells if pasting a number of values is important.

Answer 3

Here's how I accomplished this without using the Worksheet_Change event
Define a Public REGEX Function in a new Module
'Public REGEX Formula
Public Function REGEX(pattern As String, cel As Range) As Boolean
Dim re As New RegExp
re.pattern = pattern
REGEX = re.Test(cel.Value)
End Function
I added this Sub to a module I named Validations. This Sub requires not only the range to validate and the regular expression pattern, but also another range to apply the REGEX formula to. The actual validation applied actually only checks that separate cell for a True or False value. This is a simplified version that assumes the validationColumn is an entire column.
'Validations Module
Sub regexValidation(cells As Range, pattern As String, validationColumn As Range, defaultValue As String)
Dim cel As Range, regexFormula As String, validationCell As Range
cells.Value = defaultValue
'Need to match true on default value or validation will always fail
pattern = "(" & defaultValue & ")|(" & pattern & ")"
For Each cel In cells
regexFormula = "=REGEX(""" & pattern & """," & cel.address & ")"
Set validationCell = validationColumn.cells(cel.Row, 1)
validationCell.Formula = regexFormula
cel.Validation.Delete
cel.Validation.Add xlValidateCustom, Formula1:="=" & Trim(validationCell.address)
Next cel
End Sub
This is how I'm calling it. In my case, this is a UserForm with a TextBox called regexPattern that contains the regular expression to apply.
'Form
Private Sub applyRegexValidation(cells As Range)
Validations.regexValidation cells, regexPattern.text, validationColumn:=cells.Parent.Range("AA:AA"), defaultValue:="Required Custom"
End Sub