MY GRID IN THE UPDATE PANEL IS NOT REFRESHING

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Ajax

ASP.NET4

Hi,
I have an gird which should refresh after a new data is being inserted into it,for which i used the update panel,but the problem is the update panel is not refreshing after the click event.

<asp:Content ID="Content3" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
    <p>
        &nbsp;</p>
    <p><asp:ScriptManager ID="MainScriptManager" runat="server" />
        <asp:UpdatePanel ID="pnlHelloWorld" runat="server"  UpdateMode="Conditional">
      
            <ContentTemplate>

            <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false" 
                    DataSourceID="SqlDataSource1">
                    <Columns>
                        <asp:BoundField DataField="username" HeaderText="username" 
                            SortExpression="username" />
                        <asp:BoundField DataField="comments" HeaderText="comments" 
                            SortExpression="comments" />
                    </Columns>
                </asp:GridView>

            <asp:Button ID="Button2" runat="server" onclick="Button2_Click" 
        style="position: relative; top: 0px; left: 0px; width: 379px" Text="Button" 
                    />
                 
            
            </ContentTemplate>

               <Triggers>
                <asp:AsyncPostBackTrigger ControlID="Button2" EventName="Click" />
                </Triggers>
            </asp:UpdatePanel>

my code behind click event:

protected void Button2_Click(object sender, EventArgs e)
        {
            string username = TextBox1.Text;
            string comments = TextBox2.Text;
            SqlConnection conn = new SqlConnection(WebConfigurationManager.ConnectionStrings["ForumDBConnectionString"].ConnectionString);//create our sql command object
            SqlCommand cmd = new SqlCommand("Insert INTO tests(username,comments) VALUES (@username, @comments)", conn);
            cmd.CommandType = CommandType.Text;
            cmd.Parameters.AddWithValue("@username", username);
            cmd.Parameters.AddWithValue("@comments", comments);

            using (conn)
            {
                conn.Open();
                cmd.ExecuteNonQuery();
            }

pls help me out