Hidden field loses value in codebehind?

Question

I am trying to pass data from my client to server using a HiddenField.

Javascript/UI.ascx

<asp:HiddenField ID="PassArgs" runat="server" EnableViewState="true"/>
//Tried using EnableViewState, but still no luck


<script>

document.getElementById("<%=PassArgs.ClientID%>").value = JSON.stringify(SP.UI.ModalDialog.get_childDialog().get_args());
alert(document.getElementById("<%=PassArgs.ClientID%>").value); 
//Alert shows correct data to be passed

</script>

However when I try to access my HiddenField from the codebehind, my result is empty.

CodeBehind

var jss = new JavaScriptSerializer();

var dict = jss.Deserialize<Dictionary<string, dynamic>>(PassArgs.Value);
//PassArgs.Value = ""     --- whyyyy???

I am posting this question as a last resort because I have spent a full work day looking at similar questions, but I am not able to get this to work for my situation.

How come my alert of 'PassArgs' contains the correct values, but my code behind shows empty? I have tried using HiddenFields, TextBoxes, and Labels, but the result is the same for all of them.

EDIT: The HiddenField seems to have the correct values when the script is run, I dont think thats the problem, but I think the script is running AFTER iv already tried to access it in the codebehind. I think that may be why the HiddenField is showing empty, because the script hasent run yet. How can I get this to run in UI.ascx before my debugger gets to the codebehind (UI.ascx.cs) to access it?

Answer 1

you can fetch data from server variables, so you can get the value by calling Request.Form["PassArgs"] which returns the value of your request , and you can parse the result of the request collection of your form Convert.ToString(Request.Form) as well

otherwise you can use the TextBox field with a hidden style in case it is still not working

<asp:TextBox ID="PassArgs" runat="server" style="display:none;"></asp:TextBox>