Question

I have created an item swapper control consisting in two listboxes and some buttons that allow me to swap items between the two lists. The swapping is done using javascript. I also move items up and down in the list. Basically when I move the items to the list box on the right I store the datakeys of the elements (GUIDs) in a hiddenfield. On postback I simply read the GUIDs from the field. Everything works great but on postback, I get the following exception:

Invalid postback or callback argument. Event validation is enabled using in configuration or <%@ Page EnableEventValidation=’true’ %> in a page. For security purposes, this feature verifies that arguments to postback or callback events originate from the server control that originally rendered them. If the data is valid and expected, use the ClientScriptManager.RegisterForEventValidation method in order to register the postback or callback data for validation.

I’ve prepared a test application. All you have to do is download the archive and run the project. On the web page select the 3 items, press Add all, then move the third element up one level and then hit ‘Button’. The error will show up. Turning event validation off is by no means acceptable. Can anyone help me, I’ve spent two already days without finding a solution.

TEST APPLICATION

Answer 1

The first option will bring considerable overhead. I have defined my own custom listbox control derived from the listbox class and performed an override of the loadpostback data:

public class CustomListBox : ListBox {     protected override bool LoadPostData(string postDataKey, System.Collections.Specialized.NameValueCollection postCollection)     {         return true;     } } 

Using this instead of the regular listbox in my user control solved the problem, however are there any risks associated with my approach?