Incremental Invoice Number using VBA - Access - vba

Question

Part of my access application does invoicing. I have an invoice number table that wholes one field "InvoiceNum". On my invoice report I have the following code:
Private Sub Report_Open(Cancel As Integer)
'lookup invoice number when invoice opens
intInvoiceNum = Nz(DLookup("InvoiceNum", "tblInvoiceNum"), 0)
End Sub`
Private Sub PageHeaderSection_Format(Cancel As Integer, FormatCount As Integer)
'Incrementally add one (1) to the invoice number for every page of in the report
Me.txtInvoiceNum = intInvoiceNum
intInvoiceNum = intInvoiceNum + 1
End Sub`
Private Sub Report_Close()
'Update tblInvoiceNum with the last invoice number in the report
db.Execute ("UPDATE InvoiceNum SET InvoiceNum = " & intInvoiceNum)
End_Sub`
Problem: My report open with groupby ClientID and ProjectNum. Multiple invoices print on the same report. If any invoice spills over to second page the Format Code runs again inserting an incremental invoice number to the second page. How can I prevent this from happening?

Answer 1

Consider using a Running Sum control with the InvoiceNum in the report's Page Header section. No VBA required.
First, add an invisible textbox for running count over all report's records with following:
Control Source: =1
Running Sum: Over All
Name: RunningCount
Visible: No
Second, add another invisible textbox for DLookUp of InvoiceNum:
Control Source: =DLookup("InvoiceNum", "tblInvoiceNum")
Running Sum: No
Name: intInvoiceNum
Visible: No
Finally, add a visible textbox for sum of prior two controls serving as the incremental Invoice Number:
Control Source: =[intInvoiceNum] + [RunningCount]
Running Sum: No
Name: IncrementalInvoiceNum
Visible: Yes
You may be wondering, why the first two invisible controls? Reason being is using Running Sum: Over All will include both the counts and invoice number for each record of the report (e.g., 1 + InvoiceNum - 1st record; 1 + 1 + InvoiceNum + InvoiceNum - 2nd record...)