Validate a TextBox before the _Change event is fired - string

Question

I've got a form that has 3 TextBox controls on it: stock code, quantity, certificate number. The stock code TextBox is set to focus automatically when the form is loaded.
I've also attached a bar code scanner to my PC, as the user wants to be able to either scan a bar code to populate the TextBox, or manually type the data in.
The labels being scanned contain two bar codes. One is a certificate number and the other a stock code.
The stock bar code has a prefix of "SBC/", whilst a certificate bar code is prefixed with "C/".
When the user scans a bar code, if the TextBox in focus is the stock code TextBox, then I want to run a check as below.
Private Sub txtStockCode_Change()
On Error GoTo errError1
If Len(txtStockCode.Text) >= 5 Then
If bChangeCode Then
If Left(txtStockCode.Text, 2) = "C/" Then
msgbox "You have scanned the certificate barcode; please scan the stock barcode."
txtStockCode.Text = ""
Else
bChangeCode = False
txtStockCode.Text = Replace(txtStockCode.Text, "SBC/", "")
txtStockCode.Text = Replace(txtStockCode.Text, "*", "")
End If
End If
End If
Exit Sub
Let's say the focus is currently on the stock code TextBox.
If the stock bar code is scanned, the following should happen:
Stock code length is greater than 5
Left 5 characters do not = "C/", so correct code has been scanned
TextBox text value is updated to remove all * and the prefix of "SBC/"
E.g. "SBC/A12-TR0*" becomes "A12-TRO"
and
Certificate number length is greater than 5
Left 5 characters do = "C/", so incorrect code has been scanned
MsgBox to user
TextBox value is reset to ""
However, no matter which code is scanned into the stock code TextBox, the value is never validated.
E.g. "SBC/A12-TR0*" remains as "SBC/A12-TR0*" and "C/29760" remains as "C/29760"
As the validation code is the same in the certificate TextBox, the same pattern is repeated vice versa.
Why are my values not updating, or how can I validate the input before the _Change is fired?
EDIT
I've now changed my code to
Private Sub txtStockCode_Change
If txtStockCode.Text <> "" Then
txtStockCode.Text = Replace(txtStockCode.Text, "SBC/", "")
txtStockCode.Text = Replace(txtStockCode.Text, "*", "")
End If
End Sub
But it still displays the prefix of SBC/, yet is removing the two * characters (at the start and end of the barcode as is required for the scanner to read it as a barcode)

Answer 1

You could try to set the barcode reader to return Enter key at the end of the scanned barcode and then use the Keypress event to check it and make your changes.
Sub txtStockCode_KeyPress(KeyAscii As Integer)
If KeyAscii = vbKeyReturn Then
If Len(txtStockCode.Text) >= 5 Then
If bChangeCode Then
If Left(txtStockCode.Text, 2) = "C/" Then
msgbox "You have scanned the certificate barcode; please scan the stock barcode."
txtStockCode.Text = ""
Else
bChangeCode = False
txtStockCode.Text = Replace(txtStockCode.Text, "SBC/", "")
txtStockCode.Text = Replace(txtStockCode.Text, "*", "")
End If
End If
End If
End If
End Sub