เมื่อเลือกข้อมูลใน Combobox แล้วให้แสดงราคาที่ดึงมาจากฐานข้อมุลมาแสดงใน Textbox C# Access

namespace Product
{
    public partial class PO : Form
    {
        private OleDbConnection connection = new OleDbConnection();
        DataSet ds = new DataSet();
        DataTable dt = new DataTable();

        public PO()
        {
            InitializeComponent();
            connection.ConnectionString = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=database\Product.accdb;";
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            connection.Open();
            OleDbCommand command = new OleDbCommand();
            command.Connection = connection;
            string query = "select * from Product ";
            command.CommandText = query;

            OleDbDataAdapter da = new OleDbDataAdapter(command);
            DataTable dt = new DataTable();
            da.Fill(dt);
            cbname.DataSource = dt;
            cbname.DisplayMember = "NamePro";
            cbname.ValueMember = "IDPro";
            connection.Close();

            txtname.Text = "";
        }

        private void btcal_Click(object sender, EventArgs e)
        {
            int amounts = 0, prices = 0, pricetotal = 0;
            prices = Convert.ToInt32(txtprice.Text);
            amounts = Convert.ToInt32(txtamount.Text);

            pricetotal = amounts * prices;

            txttotal.Text = pricetotal.ToString();
        }

        private void btadd_Click(object sender, EventArgs e)
        {
            try
            {
                if (connection.State == ConnectionState.Open)
                {
                    connection.Close();
                }
                connection.Open();
                OleDbCommand command = new OleDbCommand();
                command.Connection = connection;

                command.CommandText = "INSERT INTO PO ([NamePO],[NamePoPro],[PricePoPro],[AmountPo],[TotalPo]) values(@Para1,@Para2,@Para3,@Para4,@Para5)";
                command.Parameters.Clear();
                command.Parameters.AddWithValue("@Para1", txtnamePO.Text);
                command.Parameters.AddWithValue("@Para2", txtname.Text);
                command.Parameters.AddWithValue("@Para3", txtprice.Text);
                command.Parameters.AddWithValue("@Para4", txtamount.Text);
                command.Parameters.AddWithValue("@Para5", txttotal.Text);

                int result = command.ExecuteNonQuery();
                if (result > 0)
                {
                    MessageBox.Show("Data Saved");
                }
                else
                {
                    connection.Close();
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show("Error" + ex);
            }
            finally
            {
                if (connection.State == ConnectionState.Open)
                {
                    connection.Close();
                }
            }

            string show;

            show = "ชื่อผู้สี่งซื้อ :" + txtnamePO.Text +
                   "\n" +
                   "ชื่อสินค้า :" + txtname.Text +
                   "\n" +
                   "ราคาสินค้าต่อหน่วย :" + txtname.Text + " บาท" +
                   "\n" +
                   "จำนวนสินค้าที่สั่ง :" + txtname.Text + " ชิ้น" +
                   "\n" +
                   "ราคารวมสินค้า :" + txtname.Text + " บาท";

            MessageBox.Show(show, "สั่งซื้อสินค้า");
        }

        private void cbname_SelectedIndexChanged(object sender, EventArgs e)
        {
            OleDbCommand command = new OleDbCommand();
            command.Connection = connection;

            if (cbname.Text == cbname.SelectedItem.ToString())
            {
                txtname.Text = cbname.Text;
            }
            else
            {
                txtname.Text = cbname.Text;
            }

        }
    }
}