Using jQuery to piggyback JSON data onto an UpdatePanel Trigger

Question

Okay, well looks like I'll have to answer my own question then. Here are the snippets people will need if you wanna do it the same way I did.

Hope it helps somebody,

Cheers, .pd.

In the page you've put the user control on, you need to catch the click that submits the updatepanel.

<script type="text/javascript">
    $(subscribeClicks);

    // for use on pages with updatepanels.  once the panel has reloaded, the jquery
    // events get slagged so we need to rebind them here.
    var prm = Sys.WebForms.PageRequestManager.getInstance();
    prm.add_endRequest(subscribeClicks);

    function subscribeClicks() {
        // catch the search button before it (partially) posts back and send
        // data 
        $('input[id*="btnSearch"]').click(function (e) {
           // this function is in a script in your usercontrol
           senddataFromUserControl('ThisPage.aspx/NameOfYourWebMethod');
        });
    }
</script>

In your usercontrol you need senddataFromUserControl to ajax your form data to the codebehind. Note the success part where the hidden element receives the Session key. And also the async : false (thanks Kevin B).

function senddataFromUserControl(url) {
    var arr = new Array();
    var ele = $('.jq_idt_selected');
    for (var i = 0; i < ele.length; i++) {
        arr.push({ Name: $(ele[i]).find('.jq_idt_path').text(), Value: $(ele[i]).find(':hidden').val() });
    }

    $.ajax({
        type: "POST",
        async: false,
        url: url,
        data: "{args:" + JSON.stringify(arr) + "}",
        dataType: "text",
        contentType: "application/json; charset=utf-8",
        success: function (data) {
            $('input[id*="hdnSessionKey"]').val($.parseJSON(data)["d"]);
        },
        error: function (data) {
            alert(data.responseText);
        }
    });
}

In your code behind, set up the class to receive name/value pairs (this one's in VB)

Public Class SearchArgs
    Public Name As String
    Public Value As String
End Class

And in C#:

public class SearchArgs {
    public string Name;
    public string Value;
}

Then code your webmethod (VB first)

<System.Web.Services.WebMethod()> _
Public Shared Function NameOfYourWebMethod(args As List(Of SearchArgs)) As String
    ' generate a session key for the client to pass back when the page postback occurs
    Dim key As String = String.Format("IDT_{0:yyMMddhhmmss}", Now)
    HttpContext.Current.Session(key) = args
    Return key
End Function

Here's a C# version:

[System.Web.Services.WebMethod()]
public static string NameOfYourWebMethod(List<SearchArgs> args)
{
    // generate a session key for the client to pass back when the page postback occurs
    string key = string.Format("IDT_{0:yyMMddhhmmss}", DateAndTime.Now);
    HttpContext.Current.Session[key] = args;
    return key;
}

Finally in the submit button click, grab the extra data from Session.

    Dim o As Object = yourUserControl.FindControl("hdnSessionKey")
    Dim hdn As HtmlInputHidden = CType(o, HtmlInputHidden)
    If hdn IsNot Nothing Then
        Dim key As String = hdn.Value
        Dim filterValues As List(Of SearchArgs) = CType(Session(key), List(Of SearchArgs))
        For Each filterValue As SearchArgs In filterValues
            ' do what you need to prep this for your data layer
        Next
        Session(key) = Nothing
    End If

And in C#:

object o = yourUserControl.FindControl("hdnSessionKey");
HtmlInputHidden hdn = (HtmlInputHidden)o;
if (hdn != null) {
    string key = hdn.Value;
    List<SearchArgs> filterValues = List<SearchArgs>)Session[key];
    foreach (SearchArgs filterValue in filterValues) {
        // do what you need to prep this for your data layer
    }
    Session[key] = null;
}