On Oct 4, 7:14 am, G?ran Andersson <gu...@guffa.com> wrote:

Goran, I am highly obliged to you for putting in so much effort & time
in trying to make me understand interfaces. I really appreciate it
from the bottom of my heart (& I really mean it). Now I am getting a
hang of interfaces & their uses. I guess you must be pleased to know
that your efforts aren't being wasted!

Finally I could make that code work. This is the class (.vb) code (I
am reproducing the entire code so that someone else can benefit from
it in the future; after all everyone won't be as fortunate as me to
have a helpful guide like you):

Imports System
Imports System.Data
Imports System.Data.SqlClient

Public Interface IDBSettings
   Property ConnectionString() As String
   Function QueryDB(ByVal qry As String) As SqlDataReader
End Interface

Public Class DBSettings
   Implements IDBSettings
   Public ConnString As String
   Private sqlCmd As SqlCommand
   Private sqlConn As SqlConnection

   Public Property ConnectionString() As String Implements
IDBSettings.ConnectionString
       Get
           ConnectionString = ConnString
       End Get
       Set(ByVal value As String)
           ConnString = value
       End Set
   End Property

   Public Function QueryDB(ByVal qry As String) As SqlDataReader
Implements IDBSettings.QueryDB
       sqlConn = New SqlConnection(ConnectionString)
       sqlCmd = New SqlCommand(qry, sqlConn)

       sqlConn.Open()
       Return sqlCmd.ExecuteReader
       sqlConn.Close()
   End Function
End Class

& this is the ASPX code:

<%@ Page Language="VB" Explicit="True" %>
<%@ Import Namespace="System.Data" %>
<%@ Import Namespace="System.Data.SqlClient" %>

<script runat="server">
   Sub Page_Load(ByVal obj As Object, ByVal ea As EventArgs)
       Dim boDBSettings As IDBSettings
       Dim sqlDReader As SqlDataReader

       boDBSettings = New DBSettings
       boDBSettings.ConnectionString = ".........."
       sqlDReader = boDBSettings.QueryDB("SELECT * FROM Table1")

       If Not (sqlDReader Is Nothing) Then
           dg1.DataSource = sqlDReader
           dg1.DataBind()

           sqlDReader.Close()
       End If
   End Sub
</script>
<form runat="server">
<asp:DataGrid ID="dg1" runat="server"/>
</form>

There is one thing I noticed when I made the reference to the
IDBSettings interface (instead of the DBSettings class) in the ASPX
code. I use Visual Web Developer 2005 for ASP.NET apps. When I typed

boDBSettings.

(notice the dot after boDBSettings), then VWD's intellisense lists
only 2 items - the property named ConnectionString & the function
named QueryDB but if I make the reference to the DBSettings class,
then apart from ConnectionString & QueryDB, VWD's intellisense also
lists other items like ConnString, Equals, GetHashCode, GetType,
ReferenceEquals, ToString etc.

So isn't this a disadvantage of using user-defined interfaces? Because
making a reference to the interface IDBSettings from the ASPX page
means I won't be able to use the built-in functions like Equals,
GetHashCode, GetType etc. (which would be available if I make the
reference to the DBSettings class instead). If I want to do the same
task which the function, say, Equals does, then I have to add more
code within the interface & the class (in the class file) which in
turn means more work for the programmer. So is using user-defined
interfaces worthwhile?

Sorry, Goran, I couldn't exactly understand the above statement. Could
you please elaborate on it a little bit (maybe with an example as I
find it easier to understand things with examples instead of just a
textual explanation)?

Thanks once again for your co-operation.

Regards.