Add multiple data GridView and Display GridView Edit Row Data in TextBox Outside GridView in ASP.NET

DataTable dt = null;
protected void Page_Load(object sender, EventArgs e) {
    if (!IsPostBack) {
        if (ViewState["Details"] == null) {
            DataTable dataTable = new DataTable();
            dataTable.Columns.Add("Name");
            dataTable.Columns.Add("Address");
            ViewState["Details"] = dataTable;
        }
    }
    //if (!this.IsPostBack)
    //{
    // DataTable dt = new DataTable();
    // dt.Columns.AddRange(new DataColumn[3] { new DataColumn("Id", typeof(int)),
    // new DataColumn("Name", typeof(string)),
    // new DataColumn("Country",typeof(string)) });
    // dt.Rows.Add(1, "John Hammond", "United States");
    // dt.Rows.Add(2, "Mudassar Khan", "India");
    // dt.Rows.Add(3, "Suzanne Mathews", "France");
    // dt.Rows.Add(4, "Robert Schidner", "Russia");
    // GridView1.DataSource = dt;
    // GridView1.DataBind();
    //}
}
protected void OnSelectedIndexChanged(object sender, EventArgs e) {
    GridViewRow row = GridView1.SelectedRow;
    // txtId.Text = row.Cells[0].Text;
    txtName.Text = row.Cells[0].Text;
    txtCountry.Text = row.Cells[1].Text;
    txtCountry.Text = (row.FindControl("lblCountry") as Label).Text;
}
protected void Button1_Click(object sender, EventArgs e) {
    // string strs = txtId.Text.Trim();
    string str = txtName.Text.Trim();
    string str1 = txtCountry.Text.Trim();
    dt = (DataTable) ViewState["Details"];
    dt.Rows.Add(str, str1);
    ViewState["Details"] = dt;
    GridView1.DataSource = dt;
    GridView1.EmptyDataText = "Name";
    GridView1.EmptyDataText = "Address";
    GridView1.DataBind();
    txtId.Text = "";
    txtName.Text = "";
    txtCountry.Text = "";
}
}