HOw to add new blank row at specific location

protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            DataTable dt =GetTable();
            GridView1.DataSource = dt;
            GridView1.DataBind();
            ViewState["Table"] = dt;
        }

    }


    protected void Button1_Click(object sender, EventArgs e)
    {
        int index = GridView1.SelectedIndex;
        //you may need to validate the index
        DataTable dt = (DataTable)ViewState["Table"];
        DataRow row = dt.NewRow();
        dt.Rows.InsertAt(row, index);
        dt.AcceptChanges();
        GridView1.DataSource = dt;
        GridView1.DataBind();
        ViewState["Table"] = dt;
    }