Ch15 CodeBehind

mahir · May 6th, 2004, 10:07 AM

Hi,

I am encoutring the problem in the last example of Ch15 I am sending the error message please help.

If u need anything else please do tell me.

Object reference not set to an instance of an object.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:

[NullReferenceException: Object reference not set to an instance of an object.]
   HeaderClass.Page_Load() +122
   System.Web.Util.ArglessEventHandlerDelegateProxy.C allback(Object sender, EventArgs e) +10
   System.Web.UI.Control.OnLoad(EventArgs e) +67
   System.Web.UI.Control.LoadRecursive() +29
   System.Web.UI.Control.LoadRecursive() +92
   System.Web.UI.Control.LoadRecursive() +92
   System.Web.UI.Page.ProcessRequestMain() +724

--------------------------------------------------------------------------------
Version Information: Microsoft .NET Framework Version:1.0.3705.0; ASP.NET Version:1.0.3705.0

Thanks

Mahir Ali Ahmed

bmains · May 6th, 2004, 12:01 PM

Hello,

Could you post the code? I don't have the book.

Thanks.

mahir · May 8th, 2004, 01:58 AM

here are the three files used in this program

main3.aspx
<%@ Page Language="VB" Debug="True" %>
<%@ Register TagPrefix="WroxUC" TagName="FeaturedBooks" Src="featuredbooks.ascx" %>
<%@ Register TagPrefix="WroxUC" TagName="Header" Src="header_CB.ascx" %>
<script runat="server">

    ' Insert page code here
    '

</script>
<html>
<head>
    <title>User Control Examples</title>
    <link href="style.css" type="text/css" rel="stylesheet" />
</head>
<body>
    <form method="post" runat="server">
        <WroxUC:Header id="MyHeader" runat="server"></WroxUC:Header>
        <br />
        <table>
            <tbody>
                <tr>
                    <td valign="top" width="70%">
                        This is the Wrox shop, where you can find out more about Wrox Books. The links take
                        you to a page on the wrox site where you can find out more details about each title.
                    </td>
                    <td width="30%">
                        <WroxUC:FeaturedBooks id="MyFeaturedBooks" runat="server"></WroxUC:FeaturedBooks>
                    </td>
                </tr>
            </tbody>
        </table>
    </form>
</body>
</html>

header_CB.vb

Imports System
Imports System.Web.UI
Imports System.Web.UI.WebControls
Imports System.Collections

Public Class HeaderClass : Inherits UserControl

    Private Languages As New Hashtable()
    Private LanguageList As DropDownList
    Private WelcomeMessage As Label

    Public Sub Page_Load()

        Languages.Add("English", "Hello, and welcome to the shop")
        Languages.Add("French", "Bonjour, et bienvenue au magasin")
        Languages.Add("Spanish", "Buenas Dias, e bienvenido a la tienda")
        Languages.Add("German", "Guten Tag, und wilkommen ins geschaeft")

        If Not Page.IsPostBack Then

            LanguageList.DataSource = Languages.Keys
            Page.DataBind()

        End If

    End Sub

    Public Sub DropList_Changed(Sender As Object, E As EventArgs)

        WelcomeMessage.Text = Languages(LanguageList.SelectedItem.Text)

    End Sub

End Class

header_CB.ascx

<%@ Control Inherits="HeaderClass" Src="header_CB.vb" Language="VB" %>
<script runat="server">

    ' Insert page code here
    '

</script>
<table style="BACKGROUND-COLOR: #cc0033" cellspacing="0" width="100%" cellpading="10">
    <tbody>
        <tr>
            <td width="10%">
                <img src="logo.gif" align="left" />
            </td>
            <td width="60%">
                <asp:Label id="WelcomeMessage" runat="server"> Welcome
                to the Wrox Shop! </asp:Label></td>
            <td widt="30%">
                Select your Language:<br />
                <asp:DropDownList id="LanguageList" runat="server" AutoPostBack="True" OnSelectedIndexChanged="DropList_Changed"></asp:DropDownList>
                </td>
        </tr>
    </tbody>
</table>

Mahir Ali Ahmed