Having issues in updating the existing controls in SDL tridion

Question

I am new to Tridion and I need to remove the dropdown from the control and the moment i do that the file gives null exception error.

Control code:
<%@ Control Language="C#" AutoEventWireup="true" Inherits="xxx.Codebehind.Controls.Listing" %>
<%@ Register Assembly="xxx.Codebehind" Namespace="xxx.Codebehind.Utilities" TagPrefix="xxx" %>

    <section class="articlesList">
         <p><%=subHeading%></p>
         <h2><%=titleText%></h2>
        <div class="liner">
            <label>##resultsPerPage##:</label>    
            <asp:DropDownList runat="server" ID="ResultsPerPage" CssClass="resultsPerPage" AutoPostBack="true">
                <asp:ListItem Value="5">5</asp:ListItem>
                <asp:ListItem Selected="True" Value="10">10</asp:ListItem>
                <asp:ListItem Value="15">15</asp:ListItem>
                <asp:ListItem Value="20">20</asp:ListItem>
                <asp:ListItem Value="25">25</asp:ListItem>
                <asp:ListItem Value="30">30</asp:ListItem>
                <asp:ListItem Value="35">35</asp:ListItem>
                <asp:ListItem Value="40">40</asp:ListItem>
                <asp:ListItem Value="45">45</asp:ListItem>
                <asp:ListItem Value="50">50</asp:ListItem>
            </asp:DropDownList>    
        </div>
        <table class="layout">
            <thead>
                <tr>
                <th>##documentArticle##</th>
                <th>##date##</th>
                </tr>
            </thead>
            <tbody>
                <asp:ListView runat="server" ID="PressReleases" >
                    <LayoutTemplate>
                        <asp:PlaceHolder runat="server" ID="itemPlaceholder" />                                            
                    </LayoutTemplate>
                    <ItemTemplate>
                        <tr>
                            <td>
                                <ul class="linkList">
                                    <li>
                                        <a <%# ((PressReleaseItem)Container.DataItem).URLMarkup %> ><%# ((PressReleaseItem)Container.DataItem).Title %></a>
                                    </li>
                                </ul>
                            </td>
                            <td><%# ((PressReleaseItem)Container.DataItem).Date.ToString("dd MMM yyyy") %></td>
                        </tr>
                    </ItemTemplate>                           
                </asp:ListView>     
            </tbody>
        </table>

        </section>

I removed all the references of the dropdown from the codebehind. It doesn't give any error or even the page is fine. But the moment i remove the the dropdown from this file it gives null exception error.

The code that i commented from the codebehind is

//DropDownList ResultsPerPage = base.FindControl("ResultsPerPage") as DropDownList;
 //itemsPerPage = int.Parse(ResultsPerPage.SelectedValue);

Any idea what may be the issue or how these dropdowns are working?

Answer 1

The good news is that nothing in your question is specific to Tridion :) So you can probably search the internet for a solution without limiting yourself to the realm of Tridion.

Now for my suggestion on what might be going wrong: you either missed a reference to the drop-down (maybe in other code files) -- or you did not rebuild and copy the DLL to the website before requesting the page again.

The code in the code-behind file gets compiled into an assembly (DLL) and if that hasn't been updated on the website, it will still try to find the drop-down list in your markup (which is compiled just-in-time), resulting in a NullReferenceException.