Question

I have an ascx control;

<%@ Control Language="C#" AutoEventWireup="true" CodeBehind="LanguageSelect.ascx.cs" Inherits="MyNamespace.LanguageSelect" %>

with code behind:

protected void Page_Load(object sender, EventArgs e)
        {
            Languages = GetSiteLanguagesService();
            if (Languages.Count > 1)
            {

                //null reference exception here!! languageDropdown is null!
                LanguageDropdown.Visible = true;
                LanguageDropdown.DataTextField = "DisplayName";
                LanguageDropdown.DataValueField = "LangUrl";
                LanguageDropdown.DataSource = Languages ;
                LanguageDropdown.DataBind();
            }
        }

inside another control:

<%@ Control Language="C#" AutoEventWireup="true" CodeBehind="SomePage.ascx.cs" Inherits="myNamespace.SomePage" %>
<div id="main" role="main"> 
    <myTag:LanguageSelect id="langSelect" runat="server" />
    <div class="section columns"> 
        <div class="main-column"> ....

With the debugger i hit on the page_load of LanguageSelect, but the dropdown is null! if i’m adding the drop down control in the markup, i thought it should always exists, in this case it is behaving like it was just a dynamic control..

now, the control SomePage is being rendered in the html, but this one in the myTag is not being rendered at all, does not matter if i wrap the dropdown list in a div, the div won’t be rendered either!!

If i put the breakpoint in the SomePage page_load, the langSelect control will be there (not null), but it itself has a null LanguageDropdown

Answer 1

Finally, figured out the problem; when the control is embedded in other control, ASP.NET assumes that you will override rendering (it will not render the sub-controls automatically)

I had to made the following changes to Page_Load, basically allocating the control:

protected void Page_Load(object sender, EventArgs e)
        {
            Languages = GetSiteLanguagesService();
            if (Languages.Count > 1)
            {

                LanguageDropdown = new DropDownList(); //allocate the control
                LanguageDropdown.Visible = true;
                LanguageDropdown.DataTextField = "DisplayName";
                LanguageDropdown.DataValueField = "LangUrl";
                LanguageDropdown.DataSource = Languages ;
                LanguageDropdown.DataBind();
            }
        }

and then, add an override for the OnRender handler:

protected override void Render(HtmlTextWriter writer)
        {
            base.Render(writer);
            LanguageDropdown.RenderControl(writer);
        }

After this, the control rendered perfectly!