I need to format a datagrid column for credit cards:
xxxxxxxxxxx2345 and still be able to edit the column.
What I tried was:
                    <asp:TemplateColumn HeaderText="DocumentNum">
                        <HeaderStyle HorizontalAlign="Center" ForeColor="White" BackColor="darkgreen" Wrap="false"></HeaderStyle>
                        <ItemStyle Wrap="false" />
                        <ItemTemplate>
                            <%#CheckLength(Container.DataItem("DocumentNumber" ))%>
                        </ItemTemplate>
                    </asp:TemplateColumn>
And

 Protected Function CheckLength(ByVal DocumentNum As Object) As String
        'I passed it as an object to stop the DBNull Error.
        If DocumentNum.ToString().Length > 14 Then
            Return "xxxxxxxxxx" & DocumentNum.SubString(5, 4)
        Else
            Return DocumentNum.ToString()
        End If
    End Function

I get an error that sustring as long not found.
The datatype for my field is bigint.

Thank you any help!

Thank you,

Thanks anyway, I found My problem, SubString does not accept BigInt (Long).

Thank you,