Have you ever encountered this error:
Invalid postback or callback argument. Â Event validation is enabled using <pages enableEventValidation=”true”/> in configuration or <%@ Page EnableEventValidation=”true” %> in a page. Â For security purposes, this feature verifies that arguments to postback or callback events originate from the server control that originally rendered them. Â If the data is valid and expected, use the ClientScriptManager.RegisterForEventValidation method in order to register the postback or callback data for validation.
That’s pretty long error message. I get this exception if I add items to drop-down control from JavaScript. The question is how to use ClientScriptManager.RegisterForEventValidation method?
First, let’s reproduce the problem. Create a new website and copy/paste this code:
<asp:DropDownList ID="dd" runat="server">
<asp:ListItem>One</asp:ListItem>
<asp:ListItem>Two</asp:ListItem>
</asp:DropDownList>
<asp:Button ID="Button1" runat="server" Text="Test" />
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js"
type="text/javascript"></script>
<script type="text/javascript">
$(function()
$("#<%= dd.ClientID %>").append($("<option />")
.val(3)
.text("Three!"));
</script>
If you select option “Three” sure enough, exception is thrown. To prevent it you need to supply all possible values for drop-down control:
protected override void Render(HtmlTextWriter writer)
Page.ClientScript.RegisterForEventValidation(dd.UniqueID, "3");
Page.ClientScript.RegisterForEventValidation(dd.UniqueID, "4");
Page.ClientScript.RegisterForEventValidation(dd.UniqueID, "11");
// and so on
base.Render(writer);
The exception is fixed but server variable for drop-down control is useless – it has no idea that you’ve added new item so dd.SelectedValue will give One, not 3. You need to read POST variable directly instead, like this:
protected void Page_Load(object sender, EventArgs e)
if (IsPostBack)
Response.Write(Request.Form[dd.UniqueID]);
Related
Thanks man, really helpful, as I just did the same type of code (including the jQuery option building 🙂 ) and encountered the same problem !
Keep posting !
If you select option “Three” sure enough, exception is thrown. To prevent it you need to supply all possible values for drop-down control:
>> meaning you really need to supply all possible value literally? how about for the dynamic values like the possible values would range from 1 to a 100. are we still gonna input that?
@Pavel Chuchuva: This is further complicated by having to run the code in the Render() event; so I fill a GridView with rows and custom postbacks, then have to repeat in the render event. However I disagree with Pavel, the event validation is important and should NOT be disabled – it’s not perfect, but it still goes a long way from preventing the page being modified by malicious code.
Great post but I could not get the Request.Form to work. The postback data didn’t contain the new data in my Listbox (html select). I inserted the data to the html select with jquery. I am using the UpdatePanel now to save me head aches. MVC 3 works so much better for this sort of thing. Thanks anyway.
Hi, thanks for the info…..i have a problem though.
im using an update panel for a drop down list with a selectedindexchange event, when am i suposse to put the “Response.Write(Request.Form[dd.UniqueID]);” if there’s only a postback on my drop down list…i tried to put it inside the selectedindexchange event, and i tried to disable the event validation, but none work….please! help!
