Turns out my previous solution was a trip down an evil rabbit hole due to reusing a global variable from my JavaScript in my code behind (doh). Here is the corrected solution, which is a bit uglier: First, in the custom control I made a public property for the listbox ClientID within the control I wished to access in my Javascript:

public partial class Controls_Locations : System.Web.UI.UserControl
{
public ListBox Locations
{
get {return lbControlVehicles.ClientID; }

}

Then in my page code behind I provided a public property for this listbox ClientID string:

private Controls_Locations userLocations;

public string UserVehiclesListBox
{
get { return userLocations.Locations; }

}

In my Page_Load I initialize userLocations:

protected void Page_Load(object sender, EventArgs e)
{
if (Page.IsPostBack == false)
{
userLocations = this._Locations1;// _Locations1 is the custom control in my aspx file which contains the listbox I want to access

In my aspx file using Javascript:

<uc1:RastracUserVehicle_Locations ID="RastracUserVehicle_Locations1" runat="server" />

<script type="text/javascript" language="javascript">

var myLocationList;

function getLocationListBox()
{
myLocationList = $get("<%=UserVehiclesListBox%>");

//myLocationList is now the listbox contained within the custom control

}

I used a "global" Javascript variable so that I only need to get the list once. I have not yet discovered whether accessing the list will cause a post back to the server everytime.

When I try this:

var foo = $find<"%=_Locations1.ClientID%>");

The dynamic page during debug shows:

var foo = $find"ctl00_ctl00_ContentPlaceHolder1_ContentPlaceHolderMain__Locations1");

and foo is null after stepping through it.

Yes I am aware of the name mangling, and have tried all my usual solutions. I will post more details and examples later. Thanks for trying to help.

I have been tasked with replacing some DOM and javascript with an ASP custom control. The aspx page is using master pages. What I need to do is access the custom control with javascript in the aspx page. The control and its C# code behind are working, but I need to access a listbox contained within the control. I seem to be unable to access the control at all. For example, in the aspx page I have the custom control like this:

;

In another page using an AJAX slider control, I have been able to access it like this:

var sliderUpdater = $find("SliderBehavior");

... then I am able to get and set properties for the slider. However, trying similar approaches with our custom control all results in returning null from the $find. Note: our control does not currently have any extenders or BehaviorID. I will post more code details if necessary. Any ideas, help, or links would be appreciated. Thank you.