Refresh child page on DropDownList change in UserControl using C# and VB.Net in ASP.Net

Last Reply one month ago By dharmendr

Posted one month ago

How to refresh child page after change in combo box located in user control

Here is my situation.

I have got #1 a master page, this master page contains #2 a child page where a #3 grid is located and a #4 user control. This user control contains a drop down box #5.

My idea is that when a user changes the item in the drop down box to refresh the grid located in the child page applying the value from the drop down as filter value.

So far, I used an autopostback on the drop down which stores the selected value in a session value, when the refresh occurs the whole page is reloaded but a SqlDataSource appears to be refreshed before the drop down updates the session value therefore, I am not showing the correct data.

Is there a better way to refresh de child page from a drop down located in a user control? Should I add a button? 

You are viewing reply posted by: dharmendr one month ago.
Posted one month ago Modified on one month ago

Hi Corobori,

Check this example. Now please take its reference and correct your code.


For this example I have used of Northwind database that you can download using the link given below.

Download Northwind Database



<asp:DropDownList runat="server" ID="ddlCountries" AutoPostBack="true" OnSelectedIndexChanged="OnCountryChanged">
    <asp:ListItem Value="0" Text="Select" />
    <asp:ListItem Value="Germany" Text="Germany" />
    <asp:ListItem Value="Mexico" Text="Mexico" />
    <asp:ListItem Value="UK" Text="UK" />
    <asp:ListItem Value="USA" Text="USA" />
    <asp:ListItem Value="Canada" Text="Canada" />


<%@ Register Src="~/UC_Country.ascx" TagName="Country" TagPrefix="uc" %>
<asp:Content ID="Content1" ContentPlaceHolderID="head" runat="Server">
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" runat="Server">
    <uc:Country ID="ucCountry" runat="server"></uc:Country>
    <hr />
    <asp:GridView runat="server" ID="gvCustomers" AutoGenerateColumns="false">
            <asp:BoundField DataField="CustomerID" HeaderText="Id" />
            <asp:BoundField DataField="ContactName" HeaderText="Name" />
            <asp:BoundField DataField="City" HeaderText="City" />



using System.Configuration;
using System.Data;
using System.Data.SqlClient;


Imports System.Configuration
Imports System.Data
Imports System.Data.SqlClient




public event EventHandler OnChangeValue;
protected void OnCountryChanged(object sender, EventArgs e)
    if (OnChangeValue != null)
        OnChangeValue(sender, e);


Public Event OnChangeValue As EventHandler
Protected Sub OnCountryChanged(ByVal sender As Object, ByVal e As EventArgs)
    RaiseEvent OnChangeValue(sender, e)
End Sub



protected void Page_Load(object sender, EventArgs e)
    ucCountry.OnChangeValue += new EventHandler(ValueChanged);

protected void ValueChanged(object sender, EventArgs e)
    DropDownList ddlCountry = (DropDownList)sender;
    string country = ddlCountry.SelectedValue.Trim();
    string conString = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    string query = "SELECT CustomerID,ContactName,City FROM Customers WHERE Country = @Country";
    using (SqlConnection con = new SqlConnection(conString))
        SqlCommand cmd = new SqlCommand(query);
        cmd.Parameters.AddWithValue("@Country", country);
        using (SqlDataAdapter sda = new SqlDataAdapter())
            cmd.Connection = con;
            sda.SelectCommand = cmd;
            using (DataTable dt = new DataTable())
                gvCustomers.DataSource = dt;


Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    ucCountry.OnChangeValue += New EventHandler(AddressOf ValueChanged)
End Sub

Protected Sub ValueChanged(ByVal sender As Object, ByVal e As EventArgs)
    Dim ddlCountry As DropDownList = CType(sender, DropDownList)
    Dim country As String = ddlCountry.SelectedValue.Trim()
    Dim conString As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
    Dim query As String = "SELECT CustomerID,ContactName,City FROM Customers WHERE Country = @Country"
    Using con As SqlConnection = New SqlConnection(conString)
        Dim cmd As SqlCommand = New SqlCommand(query)
        cmd.Parameters.AddWithValue("@Country", country)
        Using sda As SqlDataAdapter = New SqlDataAdapter()
            cmd.Connection = con
            sda.SelectCommand = cmd

            Using dt As DataTable = New DataTable()
                gvCustomers.DataSource = dt
            End Using
        End Using
    End Using
End Sub