Loading items from WebService

[Alex]

I have a textbox and a listbox that displays customer information. On page load my listbox populates just fine from a webmethod and shows in a ClientItemTemplate. I want to be able to call this webmethod from code-behind and repopulate the listbox based on what text is typed in the textbox (onkeyup). The problem is I keep getting the error "JavaScript runtime error: Object doesn't support property or method 'get_parent'"

 

Here is the server-side code:

<WebMethod()> _
    Public Shared Function GetCustomers() As RadListBoxItemData()
        Dim data As DataTable = GetData("248")

        Dim result As New List(Of RadListBoxItemData)()

        For i As Integer = 0 To data.Rows.Count - 1
            Dim itemData As New RadListBoxItemData()

            Dim FullName As String = data.Rows(i)("FName").ToString() & " " & data.Rows(i)("LName").ToString()
            itemData.Text = data.Rows(i)("CPhone").ToString()
            itemData.Value = data.Rows(i)("CPhone").ToString()
            itemData.Attributes.Add("FullName", FullName)
            itemData.Attributes.Add("Phone", data.Rows(i)("CPhone").ToString().Insert(0, "(").Insert(4, ") ").Insert(9, "-"))

            '--Determine opt-in icon
            Select Case data.Rows(i)("OptIn").ToString()
                Case -1
                    itemData.Attributes.Add("OptIn", "<img alt='Opted-In' src='images_zw/OptIn_OptedIn.png' />")
                Case 0
                    itemData.Attributes.Add("OptIn", "<img alt='Blocked / Opted-Out' src='images_zw/OptIn_Blocked.png' />")
                Case 1
                    itemData.Attributes.Add("OptIn", "<img alt='Pending Opt-In' src='images_zw/OptIn_Pending.png' />")
                Case 2
                    itemData.Attributes.Add("OptIn", "")
            End Select

            result.Add(itemData)
        Next

        Return result.ToArray()
    End Function

 

Here is my client-side code:

<script type="text/javascript">
        function Generate()
        {
            var listbox = $find("<%= lstContacts.ClientID%>");
            var result = PageMethods.GetCustomers(function (response) {
                response.forEach(function (listitem) {
                    listbox.trackChanges();
                    listbox.get_items().add(listitem);
                    listbox.commitChanges();
                });
                //listbox.insertItems(response);
            });
        }
    </script>

    <div>

        <div><telerik:RadTextBox runat="server" id="txtSearch" AutoPostBack="False" onkeyup="Generate();" Text="248"></telerik:RadTextBox></div>

        <div>
            <telerik:RadListBox runat="server" ID="lstContacts" width="300" height="500" AutoPostBack="False">
                <ClientItemTemplate>
                    <div class="Search_Conversation_Container">
                        <div class="Search_OptIn">
                            #= Text #
                        </div>
                    </div>
                </ClientItemTemplate>
                <WebServiceSettings Path="testlist.aspx" Method="GetCustomers"></WebServiceSettings>
            </telerik:RadListBox>

        </div>
    </div>

[Alex]

In the javascript I have tried both .insertItems(response) and .add(listitem) and both result in the same get_parent error