Sys.Application.add_init Not Invoked on UpdatePanel Update

I have a custom UI control which has a JavaScript class written around the AJAX.NET framework. It inherits from the Sys.UI.Control. The control itself is a UserControl. In the render method I wrap the control in a span and give the span's id the ClientID of the user control. This way I can do this later on:

var control = $find('<%= ServerControlID.ClientID %>');

This allows me to get the client object that represents the UI control.

I create the control in Javascript by doing this (also in the render method)

writer.Write(@"<script type='text/javascript'>
Sys.Application.add_init(function() {
debugger;
    $create(General.Filters.AccountGroupFilter,
        " + GetProperties() + @",
        null,
        null,
        $get('" + this.ClientID + @"'));
});
</script>");

This creates the object. It's done inside of the init event of the life cycle.

The problem is that this control is wrapped inside of an UpdatePanel by a consuming page/control. When another control initiates an update all the controls' UIs get redrawn, BUT the init event NEVER FIRES again.

What happens then is when I do this:

var control = $find('<%= ServerControlID.ClientID %>');
if(control != null)
  control.doSomething();

Nothing happens because the $find does not find the control after the AJAX call. I know I'm NOT doing this correctly. Where am I going wrong. The MSDN article for this stuff is pointing me in circles!

EDIT: Figured I'd include the Render method that I'm doing in the UserControl.cs portion

    protected override void Render(HtmlTextWriter writer)
    {
        writer.Write("<span id=\"" + this.ClientID + "\" >");
        writer.Write(@"<script type='text/javascript'>
        Sys.Application.add_init(function() {

        $create(TradePMR.OMS.Resources.UserControls.General.Filters.AccountGroupFilter,
        " + GetProperties() + @",
        null,
        null,
        $get('" + this.ClientID + @"'));
        });
        </script>");

        base.开发者_运维技巧Render(writer);
        writer.WriteEndTag("span");
    }

You don't need to write all that Sys.Application.add_init stuff yourself; implement IScriptControl as per this MSDN article.

The key is the part about RegisterScriptControl and RegisterScriptDescriptors, which registers your control with the ScriptManager so that an async postback will recreate your client control as necessary.

As a footnote, there is a seperate but similar article here if you are implementing Sys.UI.Behavior instead.