How to clear a textbox from PageIndexChanged event

Anurag,
To determine that the callback is caused by changing the page index, use client-side properties enabled by the CustomJsProperties event.
Attached is a sample project illustrating this approach in action. Hope this helps.
BTW: Note that you can change hidden field values directly within the ASPxGridView.PageIndexChanged event handler.
Thanks,
Alex

Hi Alex,
Ideally I would like to change the hidden field value in pageindexchanged event but when I tried it didn't worked. the code is as given below. If I change these to ASPTextBox I can see the value is not set to blank.
string selectedContactInfoIds = hidSelectedContactInfoIds.Value.Trim();
            if (selectedContactInfoIds.EndsWith(","))
            {
                selectedContactInfoIds = selectedContactInfoIds.Substring(0, (selectedContactInfoIds.Length - 1));
            }
            string[] arrSelectedContactInfoIds = selectedContactInfoIds.Split(',');
            for (int i = 0; i < arrSelectedContactInfoIds.Length; i++)
            {
                if (arrSelectedContactInfoIds[i] != string.Empty && !SelectedCustomerIds.Contains(Convert.ToInt32(arrSelectedContactInfoIds[i])))
                    SelectedCustomerIds.Add(Convert.ToInt32(arrSelectedContactInfoIds[i]));
            }
hidSelectedContactInfoIds.Value = string.Empty;
            string unSelectedContactInfoIds = hidUnSelectedContactInfoIds.Value.Trim();
            if (unSelectedContactInfoIds.EndsWith(","))
            {
                unSelectedContactInfoIds = unSelectedContactInfoIds.Substring(0, (unSelectedContactInfoIds.Length - 1));
            }
            string[] arrUnSelectedContactInfoIds = unSelectedContactInfoIds.Split(',');
            for (int i = 0; i < arrUnSelectedContactInfoIds.Length; i++)
            {
                if (arrUnSelectedContactInfoIds[i] != string.Empty && SelectedCustomerIds.Contains(Convert.ToInt32(arrUnSelectedContactInfoIds[i])))
                    SelectedCustomerIds.Remove(Convert.ToInt32(arrUnSelectedContactInfoIds[i]));
            }
hidUnSelectedContactInfoIds.Value = string.Empty;

Hi Anurag,
Thanks for the response. I'm afraid this behavior is by design.
As mentioned in the Q142094 thread, it's not quite correct to modify other controls during the ASPxGridView callback.
To modify hidden fields within the PageIndexChanged event handler, you might need to disable callbacks (see the ASPxGridView.EnableCallBacks property) and place both the text box and grid control onto the UpdatePanel. Let me know whether this makes sense.
Thanks,
Alex