RegisterForEventValidation can only be called during Render

Question

I have a webmethod which will be called from jquery ajax:

[WebMethod]
public string TestMethod(string param1, string param2)
{
    StringBuilder b = new StringBuilder();
    HtmlTextWriter h = new HtmlTextWriter(new StringWriter(b));
    this.LoadControl("~/Pages/Controls/Listing.ascx").RenderControl(h);
    string controlAsString = b.ToString();
    return controlAsString;
}

(it's a non-static method and we are able to hit it. That's not an issue)

When the loadControl() method is executed, I get an error saying: RegisterForEventValidation can only be called during Render.

I have already included EnableEventValidation="false" for the current aspx, disabled viewstate also. but still i get the same error. Any ideas on this?

Answer 1

Solution is to disable the Page's Event Validation as

<%@ Page ............ EnableEventValidation="false" %>

and Override VerifyRenderingInServerForm by adding following method in your C# code behind

public override void VerifyRenderingInServerForm(Control control)
{
    /* Confirms that an HtmlForm control is rendered for the specified ASP.NET
       server control at run time. */
}

Refer the Below Link

http://www.codeproject.com/Questions/45450/RegisterForEventValidation-can-only-be-called-duri

Answer 2

As per Brian's second link, without hopping further, just do this:

StringBuilder sb = new StringBuilder();
StringWriter sw = new StringWriter(sb);
Html32TextWriter hw = new Html32TextWriter(sw);

Page page = new Page();
HtmlForm f = new HtmlForm();
page.Controls.Add(f);
f.Controls.Add(ctrl);
// ctrl.RenderControl(hw); 
// above line will raise "RegisterForEventValidation can only be called during Render();"
HttpContext.Current.Server.Execute(page, sw, true);
Response.Write(sb); 

Answer 3

You need to notify ASP.Net that not to validate the event by setting the EnableEventValidation flag to false.

You can set it in the Web.Config in the following way

<%@ Page Language="C#" AutoEventWireup="true" EnableEventValidation = "false"