VBA - How to check if a String is a valid hex color code? - vba

Question

To prevent errors, I need to check if a String retrieved from a custom input box is not a valid hex color code. So far I found various solutions for other languages, but none for VBA.
Working on the following code, giving a not hex value input will cause a run time error. That's critical to my project, since I am working on a protected sheet.
Public Function HexWindow(MyCell As String, Description As String, Caption As String)
Dim myValue As Variant
Dim priorValue As Variant
priorValue = Range(MyCell).Value
myValue = InputBox(Description, Caption, Range(MyCell).Value)
Range(MyCell).Value = myValue
If myValue = Empty Then
Range(MyCell).Value = priorValue
End If
tHex = Mid(Range(MyCell).Text, 6, 2) & Mid(Range(MyCell).Text, 4, 2) & Mid(Range(MyCell).Text, 2, 2)
Range(MyCell).Interior.Color = WorksheetFunction.Hex2Dec(tHex)
End Function
How can I set a condition that recognizes a value not being in the format of "#" & 6 characters from 0-9 and A-F in any case?

Answer 1

Couple ways to do this. The easiest way is with a regular expression:
'Requires reference to Microsoft VBScript Regular Expressions x.x
Private Function IsHex(inValue As String) As Boolean
With New RegExp
.Pattern = "^#[0-9A-F]{1,6}$"
.IgnoreCase = True 'Optional depending on your requirement
IsHex = .Test(inValue)
End With
End Function
If for some reason that doesn't appeal to you, you could also take advantage of VBA's permissive casting of hex strings to numbers:
Private Function IsHex(ByVal inValue As String) As Boolean
If Left$(inValue, 1) <> "#" Then Exit Function
inValue = Replace$(inValue, "#", "&H")
On Error Resume Next
Dim hexValue As Long
hexValue = CLng(inValue) 'Type mismatch if not a number.
If Err.Number = 0 And hexValue < 16 ^ 6 Then
IsHex = True
End If
End Function

Answer 2

I would use regular expressions for this. First you must go to Tools-->Referencesin the VBA editor (alt-f11) and make sure this library is checked
Microsoft VBScript Regular Expressions 5.5
Then you could modify this sample code to meet your needs
Sub RegEx_Tester()
Set objRegExp_1 = CreateObject("vbscript.regexp")
objRegExp_1.Global = True
objRegExp_1.IgnoreCase = True
objRegExp_1.Pattern = "#[a-z0-9]{6}"
strToSearch = "#AAFFDD"
Set regExp_Matches = objRegExp_1.Execute(strToSearch)
If regExp_Matches.Count = 1 Then
MsgBox ("This string is a valid hex code.")
End If
End Sub
The main feature of this code is this
objRegExp_1.Pattern = "#[a-z,A-Z,0-9]{6}"
It says that you will accept a string that has a # followed by any 6 characters that are a combination of upper case or lower case strings or numbers 0-9. strToSearch is just the string you are testing to see if it is a valid color hex string. I believe this should help you.
I should credit this site. You may want to check it out if you want a crash course on regular expressions. They're great once you learn how to use them.