Text box undo not working if there is a duplicate.

[New.User]

Hello All,
I am having a form with a textbox and a list box. I want to enter a new record into the textbox to populate the table and listbox (listbox row source is the table). I have written a code to prevent duplicate entry into the table. When there is a duplicate entry I am getting a pop up to alert the user. What is not working is the undo option to clear the textbox. The code is pasted below with some required info.Any help with the code will be appreciated.
Cross posted by my partner https://stackoverflow.com/questions/...is-a-duplicate.

Table name: tblNewComponents
Field name: NewComponents
Textbox name: TextCOMPONENTS

Private Sub TextCOMPONENTS_AfterUpdate()
Dim NewComponent As String
Dim stLinkCriteria As String
Dim custNo As Integer


'Assign the entered customer name to a variable NewCustomer


NewComponent = Me.TextCOMPONENTS.Value
stLinkCriteria = "[NewComponents] = " & "'" & NewComponent & "'"
If Me.TextCOMPONENTS = DLookup("[NewComponents]", "tblNewComponents", stLinkCriteria) Then
MsgBox "This Component, " & NewComponent & ", has already been entered in database." _
& vbCr & vbCr & "Please check the component name again.", vbInformation, "Duplicate information"

Me.Undo
'undo the process and clear all fields
End If
End Sub

Regards
New User

[isladogs]

Prevention is better than cure
Use the before update event to check for and block any duplicates BEFORE these are written to the database

Or you could also index your NewComponent field and set as No Duplicates

[New.User]

Hello again Ridders,
I tried repeating for Before Update but it doesnt work, gives the same result as After Update. I wonder if I have made any mistake in the code. I am a novice and experimenting so apologize if there is any silly mistake in the code.

[New.User]

It is working now after I added the below code instead of undo.
Me.TextCOMPONENTS.Value = Null
Me.TextCOMPONENTS.SetFocus