Auto refresh ASP.Net DropDownList without page refresh using jQuery AJAX and JSON in C# and VB.Net

Hi rakeshkuma,

Add HiddenField and set the valuein DropDownList change.

Then inside Ajax success set the selected value from DropDownList.

Refer below code.

Database

I have made use of the following table Customers with the schema as follows.

I have already inserted few records in the table.

You can download the database table SQL by clicking the download link below.

Download SQL file

HTML

<asp:DropDownList ID="ddlCustomers" runat="server">
</asp:DropDownList>
<asp:HiddenField ID="hfCountry" runat="server" />
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
<script type='text/javascript'>
    $(function () {
        BindDropDownList();
        $('[id*=ddlCustomers]').on('change', function () {
            $('[id*=hfCountry]').val($(this).find('option:selected').val());
        });
    })

    setInterval(function () {
        BindDropDownList();
    }, 2000);

    function BindDropDownList() {
        $.ajax({
            type: "POST",
            url: "Default.aspx/GetCustomers",
            data: '{}',
            contentType: "application/json; charset=utf-8",
            dataType: "json",
            success: function (r) {
                var ddlCustomers = $("[id*=ddlCustomers]");
                ddlCustomers.empty().append('<option selected="selected" value="0">Please select</option>');
                $.each(r.d, function () {
                    ddlCustomers.append($("<option></option>").val(this['Value']).html(this['Text']));
                });

                if ($('[id*=hfCountry]').val() != "") {
                    $(ddlCustomers).val($('[id*=hfCountry]').val());
                }
            }
        });
    }
</script>

Namespaces

C#

using System.Data;
using System.Data.SqlClient;
using System.Configuration;
using System.Web.Services;

VB.Net

Imports System.Data
Imports System.Data.SqlClient
Imports System.Configuration
Imports System.Web.Services

Code

C#

[WebMethod]
public static List<ListItem> GetCustomers()
{
    string query = "SELECT Country FROM Customers";
    string constr = ConfigurationManager.ConnectionStrings["conString"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        using (SqlCommand cmd = new SqlCommand(query))
        {
            List<ListItem> customers = new List<ListItem>();
            cmd.CommandType = CommandType.Text;
            cmd.Connection = con;
            con.Open();
            using (SqlDataReader sdr = cmd.ExecuteReader())
            {
                while (sdr.Read())
                    customers.Add(new ListItem()
                    {
                        Value = sdr["Country"].ToString(),
                        Text = sdr["Country"].ToString()
                    });
            }
            con.Close();
            return customers;
        }
    }
}

VB.Net

<WebMethod>
Public Shared Function GetCustomers() As List(Of ListItem)
    Dim query As String = "SELECT Country FROM Customers"
    Dim constr As String = ConfigurationManager.ConnectionStrings("conString").ConnectionString
    Using con As SqlConnection = New SqlConnection(constr)
        Using cmd As SqlCommand = New SqlCommand(query)
            Dim customers As List(Of ListItem) = New List(Of ListItem)()
            cmd.CommandType = CommandType.Text
            cmd.Connection = con
            con.Open()
            Using sdr As SqlDataReader = cmd.ExecuteReader()
                While sdr.Read()
                    customers.Add(New ListItem() With {
                        .Value = sdr("Country").ToString(),
                        .Text = sdr("Country").ToString()
                    })
                End While
            End Using
            con.Close()
            Return customers
        End Using
    End Using
End Function