callback implementation

[abhi81]

Hi All,

I was trying to implement the callback functionality to dynamically populate a second dropdown based on the value of the first 1 .....a very simple task but all my tries failed.

I have the first dropdown populated from a table for countries and second dropdown again populated by a table for states in that country. I have them both populated during the page load based on the default values.

Now i want the state dropdown to reload with new values from the table based on the country when the country is changed through a callback rather than a postback. I tried to manipulate the msdn code but wasn;t successfull.

Note:
->i am trying to implement it on page based on a master page.
->am using vb.net in vs2005

Also before trying this i used the sample code provided by microsoft (

http://msdn2.microsoft.com/en-us/library/ms178209(VS.80).aspx

) and tested it on a new page and it worked fine as described however when i copied the same code over to a page which was based on a master page it was giving me a javascript error saying "ReceiveServerData is undefined"(javascript function to receive the result back from server).

Can some one please provide me with proper guidance/code to get this accomplished(even on a page based on a master page)? Am trying to implement callback for the first time.

I am also putting the case that i tried:
Default2.aspx

<%@ Page Language="VB" MasterPageFile="~/Administrator/SuperAdmin.master" AutoEventWireup="false" CodeFile="Default2.aspx.vb" Inherits="Administrator_Default2" title="Untitled Page" %>

<asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
<script type="text/javascript">

function LookUpStock()
{

var lb = document.getElementById("ListBox1");
var product = lb.options[lb.selectedIndex].text;

CallServer(product, "");
}



function ReceiveServerData(rValue)
{

document.getElementById("ResultsSpan").innerHTML = rValue;
}

</script>
<div>

<asp:ListBox ID="ListBox1" Runat="server"></asp:ListBox>

<br />

<br />

<button type="Button" onclick="LookUpStock()">Look Up Stock</button>

<br />

<br />

Items in stock: <span id="ResultsSpan" runat="server"></span>

<br />

</div>
</asp:Content>



Default2.aspx.vb

Partial Class Administrator_Default2
Inherits System.Web.UI.Page

Implements System.Web.UI.ICallbackEventHandler
Protected catalog As ListDictionary

Protected returnValue As String

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Dim cbReference As String

cbReference = Page.ClientScript.GetCallbackEventReference(Me, _
"arg", "ReceiveServerData", "context")

Dim callbackScript As String = ""

callbackScript &= "function CallServer(arg, context) { " & _
cbReference & "} ;"

Page.ClientScript.RegisterClientScriptBlock(Me.GetType(), _
"CallServer", callbackScript, True)

' Populate List Dictionary with invented database data

catalog = New ListDictionary()
catalog.Add("monitor", 12)

catalog.Add("laptop", 10)
catalog.Add("keyboard", 23)

catalog.Add("mouse", 17)
ListBox1.DataSource = catalog

ListBox1.DataTextField = "key"

ListBox1.DataBind()

End Sub

Public Sub RaiseCallbackEvent(ByVal eventArgument As String) _
Implements System.Web.UI.ICallbackEventHandler.RaiseCallbackEvent

If catalog(eventArgument) Is Nothing Then

returnValue = "-1"

Else

returnValue = catalog(eventArgument).ToString()

End If

End Sub

Public Function GetCallbackResult() _As String Implements _
System.Web.UI.ICallbackEventHandler.GetCallbackResult

Return returnValue

End Function
End Class

The exact same code runs fine if i implement it on a standalone page. But since this is based on a master page may be there is some other way to do it that i am not aware of.