how to add a textbox and dropdownlist vales into gridview view in asp.net by using Vb language?

Imports System.Data
Imports System.Data.SqlClient
Imports System.Configuration
Partial Class ServiceInvoice
Inherits System.Web.UI.Page
Dim con As New SqlConnection
Dim cmd As New SqlCommand
Dim dr As SqlDataReader
Dim dt As New DataTable

Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click

Dim dt As New DataTable
Dim i As Integer
i = GridView1.Rows.Count

Dim gvr As New DataTable
gvr.Columns.Add(i + 1)
gvr.Columns.Add(DropDownList15.SelectedValue.ToString)
gvr.Columns.Add(DropDownList16.SelectedValue.ToString)
gvr.Columns.Add(TextBox3.Text)
gvr.Columns.Add(TextBox4.Text)

End Sub

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
dt.Columns.Add(New DataColumn(" S.NO "))
dt.Columns.Add(New DataColumn(" TOOLS "))
dt.Columns.Add(New DataColumn(" UNIT PRICE "))
dt.Columns.Add(New DataColumn(" SALES QTY "))
dt.Columns.Add(New DataColumn(" AMOUNT "))

Dim dr As DataRow
dr = dt.NewRow
dt.Rows.Add(dr)
dt.AcceptChanges()
GridView1.DataSource = dt
GridView1.DataBind()

End Sub

Thanks for your comment.

This is what i did but unable to add row into grid view