Data Grid View is not showing data. C#

Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index

 public Form1()
        {
            InitializeComponent();
        }
        int buyItem = 0;
        connection con = new connection();

  private void btnOk_Click(object sender, EventArgs e)
        {


            dataGridView1.Rows[buyItem].Cells[0].Value = buyItem + 1;
            dataGridView1.Rows[buyItem].Cells[1].Value = txtItemno.Text;
            dataGridView1.Rows[buyItem].Cells[2].Value = cbxItem.Text;
            dataGridView1.Rows[buyItem].Cells[3].Value = cbxBrand.Text;
            dataGridView1.Rows[buyItem].Cells[4].Value = txtQty.Text;
            dataGridView1.Rows[buyItem].Cells[5].Value = txtPrice.Text;
            dataGridView1.Rows[buyItem].Cells[6].Value = txtPoint.Text;
            dataGridView1.Rows[buyItem].Cells[7].Value =txtLineTotal.Text;

            buyItem++;
}