how to add new row in gridview on button click?

protected void Button1_Click(object sender, EventArgs e)
   {
        DataTable dt = new DataTable();
        DataColumn dc = new DataColumn();

       if (dt.Columns.Count == 0)
        {
            dt.Columns.Add("PayScale", typeof(string));
            dt.Columns.Add("IncrementAmt", typeof(string));
            dt.Columns.Add("Period", typeof(string));
        }

        DataRow NewRow = dt.NewRow();
        NewRow[0] = TextBox1.Text;
        NewRow [1]=TextBox2.Text;
        dt.Rows.Add(NewRow); 
        GridView1.DataSource = dt;
        GridViewl.DataBind();

   }