Return Original Cell Value Is User Value Entered Is Invalid

[Ark68]

I have a cell on my worksheet that gets autopopulated with a value. The user can access the cell and change the value (a date).
I'm looking for some help in error checking. The value entered can only be a date, and it can only be a Friday. If it isn't, I'd like the cell to return to it's original value. Is this possible. I want to think it has something to do with "Cancel" but I don't know how touse it in this situation.

Here is my code ...

Private Sub worksheet_change(ByVal Target As Range)
    If Target.Address = "$C$4" Then
        uidate = Target.Value 'user inpute date
        If Weekday(uidate) <> 6 Then 'date entered isn't a friday
            'can only be a friday. Return original value to cell C4
        End If
    End If
End Sub

Is anyone able to help me find a solution to return the original value to D4. I think I can use "isdate" to determine if the value the user entered is indeed a date vs. text or some redundant entry.

 

[Rick Rothstein]

I think something like this should work...

Private Sub Worksheet_Change(ByVal Target As Range)
    Dim uidate As Variant
    Application.EnableEvents = False
    On Error GoTo Whoops
    If Target.Address = "$C$4" Then
        uidate = Target.Value
        If Weekday(uidate) <> 6 Then
            Application.Undo
        End If
    End If
    Application.EnableEvents = True
    Exit Sub
Whoops:
    Application.Undo
    Application.EnableEvents = True
End Sub

 

[Ark68]

Thank you Rick. I'm grateful for your help.
This works wonderfully.