How to call VBA function from excel - excel

Question

I have en excel file where i have to put validation rule. I have one cell let says "customer Time" where user can enter time but it is customize time. User can enter time like that
23:45
98:20
100:30
User cannot enter string and no special character except colon. I have made one macro and it works perfectly accoriding to customer demand. Here is macro
Public Function isValidTime(myText) As String
Dim regEx
Set regEx = New RegExp 'Regular expression object
regEx.Pattern = "^[0-9]+([:]+[0-9]+)*$" ' Set pattern.
If regEx.test(myText) Then
isValidTime = myText
Else
isValidTime = "Null"
End If
End Function
Note: To test this macro you have to go to VBA ide in Tool then reference and then select microsoft visual basic vbascript 5.5
Now i want to call this at excel. I can call like =IsValidTime("23:43") and getting result but customer is not interested to call this. Customer need a excel where he/she enter the value and value will validate according to above criteria and get the exact value or Null.
I dont know how to fix this task. I have Validated date and time as well from Data and then data validation and set the rule and it works perfect, i need the same way for my this rule as well. Any help will be highly appreciated...
Thanks
Kazmi

Answer 1

You can use the Worksheet_Change event inside the sheet. Inside the VBE, select the sheet and choose Workhseet from the left drop-down and Change from the right.
Enter the following code:
Option Explicit
Private Sub Worksheet_Change(ByVal Target As Range)
If Target.Address = "$A$1" Then 'assumes user input cell is A1
With Application
.ScreenUpdating = False
.EnableEvents = False
End With
On Error GoTo ErrTrap
Target.Value = isValidTime(Target.Value)
End If
KeepMoving:
With Application
.ScreenUpdating = True
.EnableEvents = True
End With
Exit Sub
ErrTrap:
MsgBox Err.Number & Err.Description
Resume KeepMoving
End Sub
Public Function isValidTime(myText) As String
Dim regEx
Set regEx = New RegExp 'Regular expression object
regEx.Pattern = "^[0-9]+([:]+[0-9]+)*$" ' Set pattern.
If regEx.test(myText) Then
isValidTime = myText
Else
isValidTime = "Null"
End If
End Function