.NET User/server Control With Custom List Items

Question

I'm attempting to create a simple menu user control just as outlined here.

The attached code results in an "Object reference not set to an instance of an object" error, but I can't figure out why. Any thoughts?

<%@ Master Language="VB" CodeFile="MySite.master.vb" Inherits="MySite" %>
<%@ Register src="Controls/Menu.ascx" tagname="Menu" tagprefix="my"  %>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>MySite</title>
    <link href="Styles/MySite.css" rel="stylesheet" type="text/css" />
    <asp:ContentPlaceHolder id="headContent" runat="server">
    </asp:ContentPlaceHolder>    
</head>
<body id="masterBody" runat="server">
    <form id="form1" runat="server">
        <my:Menu ID="Menu1" runat="server">
            <MenuItems>
                <my:MenuItem Text="Test" NavigateUrl="~/Default.aspx" />
            </MenuItems>
         </my:Menu>
    </form>
</body>
</html>

Partial Class Controls_Menu
        Inherits System.Web.UI.UserControl

    Private m_Items As List(Of MenuItem) = Nothing
        <PersistenceMode(PersistenceMode.InnerProperty)> _
        Public Property MenuItems() As List(Of MenuItem)
            Get
                Return m_Items
            End Get
            Set(ByVal value As List(Of MenuItem))
                m_Items = value
            End Set
        End Property

    End Class

    Public Class MenuItem
        Private m_Text As String
        Public Property Text() As String
            Get
                Return m_Text
            End Get
            Set(ByVal value As String)

            End Set
        End Property
        Private m_NavigateUrl As String
        Public Property NavigateUrl() As String
            Get
                Return m_NavigateUrl
            End Get
            Set(ByVal value As String)
                m_NavigateUrl = value
            End Set
        End Property
    End Class

score 0 · Answer 1 · answered Feb 18 '11 at 20:41

0

The problem is that here:

<MenuItems>
     <my:MenuItem Text="Test" NavigateUrl="~/Default.aspx" />
</MenuItems>

ASP.net is trying to Add to your MenuItems list, it does this by calling

MenuItems.Add(...)

However, since m_Items is equal to Nothing, this gives you the error. To fix this replace

Private m_Items As List(Of MenuItem) = Nothing

With

Private m_Items As List(Of MenuItem) = New List(Of MenuItem)()

answered Feb 18 '11 at 20:41

spaetzel

1,252
3
16
23

Are you displaying the MenuItem.Text? If so, you should change Private m_Text As String To Private m_Text As String = "" To avoid the null problem when displaying MenuItem.Text If you are still getting the problem, can you post the full Error message including the stack trace? – spaetzel Feb 18 '11 at 20:55
My page is exactly as shown in the code -- I'm not displaying anything as of yet. Error 2 Object reference not set to an instance of an object. C:\Websites\MySite\MySite.master 58 – Andy Feb 18 '11 at 21:03
Please post the text for Menu.ascx – spaetzel Feb 18 '11 at 21:11
`<%@ Control Language="VB" AutoEventWireup="false" CodeFile="Menu.ascx.vb" Inherits="Controls_Menu" %> ` – Andy Feb 18 '11 at 21:15

.NET User/server Control With Custom List Items

1 Answers1