how to iplement follwing functunality?

You need to use a ComboBox instead of a TextBox. Further, you don't want to necessarily change the contents of the combobox. You merely want to change the selection based on the currently typed text. Changing the binding every time a character is typed is going to cause too much overhead.

This Functionality is called as AutoComplete TextBox
in asp.net 3.5 it supports AjaxControlToolKit which is open source & can be used in ur application.
First Download AjaxControlToolKit from Following Location.

http://ajaxcontroltoolkit.codeplex.com/[^]

Then in ur asp.net bin Folder Copy the dll of AjaxControlToolKit.

& add Following Line of code at top of ur asp.net page.

<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="cc1" %>

Add ScriptManager to page, Which required for Ajax Application.

<asp:ScriptManager ID="ScriptManager1" runat="server">
    </asp:ScriptManager>

Add One WebService file(.asmx) into ur project.

after adding .asmx file .cs file will saved in App_code Folder. add this type of method in .cs file.

[WebMethod(EnableSession = true)]
    public string[] ItemName(string prefixText,int count)
    {
        int branchId = (int)Session["BranchId"];
        using (var db = new WanaDCDataContext())
        {
            var items = new List<String>();
            JavaScriptSerializer serailizer = new JavaScriptSerializer();
            var list = (from it in db.ItemMasters where it.BranchId == branchId && (it.ItemName).ToLower().StartsWith(prefixText) orderby it.ItemName ascending select it).Take(count);
            foreach (ItemMaster c in list)
            {
                var html = c.ItemId;
                //var item = AjaxControlToolkit.AutoCompleteExtender.CreateAutoCompleteItem(c.ItemName, c.ItemId);
                string item = AutoCompleteExtender.CreateAutoCompleteItem(c.ItemName, serailizer.Serialize(html));
                items.Add(item);
            }
            return items.ToArray();


        }
    }

This is Web Service Methods Which Returns String array. i have used linq To SQL Classes to retrieve data from Database.


Then call this web service from asp.net page as below.

<cc1:AutoCompleteExtender ID="AutoCompleteExtender1" TargetControlID="txtStkItem"
                                        OnClientItemSelected="OnItemSelected" CompletionSetCount="60" ServiceMethod="ItemName"
                                        ServicePath="AjaxAutoCompleteService.asmx" MinimumPrefixLength="1" CompletionInterval="100"
                                        CompletionListCssClass="completionList" CompletionListItemCssClass="listItem"
                                        CompletionListHighlightedItemCssClass="itemHighlighted" runat="server">
                                    </cc1:AutoCompleteExtender>

Make Sure You specify correct service Method,Service Path. reply for any difficulty.

Thanks & Regards,
satya.