รบกวนถามเรื่อง การดึงค่าจาก DataGridView มาโชวใน TextBox เมื่อ คลิกที่แถวใดๆขณะที่รันโปรแกรมอยู่ครับ

TextBox1.Text = DataGridView1.Rows(e.RowIndex).Cells(0).ToString;

private void dataGridView1_CellContentClick(object sender, DataGridViewCellEventArgs e)
        {
            
            string MyConString = "SERVER=localhost;" +
              "DATABASE=test;" +
              "UID=root;" +
              "PASSWORD=1234;";
            MySqlConnection connection = new MySqlConnection(MyConString);
            MySqlCommand command = connection.CreateCommand();
            MySqlDataReader Reader;
            command.CommandText = "select rental.ID_Member from rental ";
            connection.Open();
            Reader = command.ExecuteReader();

            string Index = dataGridView1.CurrentRow.Index.ToString();
            int Number = -1;

            while (Reader.Read())
            {
                Number += 1;
                if (Index == Convert.ToString(Number))
                {
                    textBox8.Text = Reader["ID_Member"].ToString();
                }


            }
        }

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using MySql.Data.MySqlClient;
using System.Data.SqlClient;


namespace Test1
{
    public partial class Form5 : Form
    {
        bool Membercheck = false;

        public Form5()
        {
            InitializeComponent();
        }

        public string _ID_Member  { get; set; }
        public string _FNAme      { get; set; }
        public string _LName      { get; set; }
        public string _ID_Book    { get; set; }
        public string _Name       { get; set; }
        public string _Start_Rent { get; set; }
        public string _End_Rent   { get; set; }


        private void Showdata1()
        {
            string MyConString = "SERVER=localhost;" +
              "DATABASE=test;" +
              "UID=root;" +
              "PASSWORD=1234;";
            MySqlConnection connection = new MySqlConnection(MyConString);
            MySqlCommand command = connection.CreateCommand();
            MySqlDataReader Reader;
            
            command.CommandText  = " SELECT M.ID_Member,M.FNAme,M.LName,B.ID_Book,B.Name,R.Start_Rent,R.End_Rent ";
            command.CommandText += " FROM  rental AS R INNER JOIN member AS M  ON R.ID_Member = M.ID_Member  ";
            command.CommandText += "                   INNER JOIN book   AS B  ON R.ID_Book   = B.ID_Book    ";
            if (Membercheck == false)
            {
                command.CommandText += " WHERE R.Re_Rent = '' ";

            }
            if (Membercheck == true)
            {
                command.CommandText += " WHERE R.ID_Member = '" + textBox1.Text + "'";

            } connection.Open();
            Reader = command.ExecuteReader();

          
            DataTable member_table = new DataTable();
            member_table.Load(Reader);
            connection.Close();

            dataGridView1.DataSource = member_table;
            dataGridView1.Columns[0].HeaderText = "รหัสสมาชิก";
            dataGridView1.Columns[1].HeaderText = "ชื่อผู้ยืม";
            dataGridView1.Columns[2].HeaderText = "นามสกุล";
            dataGridView1.Columns[3].HeaderText = "รหัสหนังสือ";
            dataGridView1.Columns[4].HeaderText = "ชื่อหนังสือที่ยืม";
            dataGridView1.Columns[5].HeaderText = "วันที่ยืม";
            dataGridView1.Columns[6].HeaderText = "กำหนดคืน";

        }

        private void dataGridView1_CellMouseDoubleClick(object sender, DataGridViewCellMouseEventArgs e)
        {
            if (e.RowIndex == -1)
            {
                return;
            }

            _ID_Member  = dataGridView1.Rows[e.RowIndex].Cells[0].Value.ToString();
            _FNAme      = dataGridView1.Rows[e.RowIndex].Cells[1].Value.ToString();
            _LName      = dataGridView1.Rows[e.RowIndex].Cells[2].Value.ToString();
            _ID_Book    = dataGridView1.Rows[e.RowIndex].Cells[3].Value.ToString();
            _Name       = dataGridView1.Rows[e.RowIndex].Cells[4].Value.ToString();
            _Start_Rent = dataGridView1.Rows[e.RowIndex].Cells[5].Value.ToString();
            _End_Rent   = dataGridView1.Rows[e.RowIndex].Cells[6].Value.ToString();

            this.Close();
        }


        private void Form5_Load(object sender, EventArgs e)
        {
            Membercheck = false;
            Showdata1();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            Membercheck = false;
            Showdata1();
            button2.Enabled = true;
            textBox1.Clear();
            textBox1.Enabled = true;
        }

        private void button2_Click(object sender, EventArgs e)
        {
            Membercheck = true;
            Showdata1();
            button2.Enabled = false;
            textBox1.Enabled = false;
        }
    }
}

private void _DGV_Dis_CellMouseDoubleClick(object sender, DataGridViewCellMouseEventArgs e)
{ 
            // กำหนดค่า Index ให้กับชื่อของตาราง Datagrid = rowClickDis
            int rowClickDis = _DGV_Dis.CurrentRow.Index;
            // กำหนดว่าแต่ละคอลัมน์ของแถวตั้งอยู่ที่ Cell หรือ คอลัมน์ที่อ้างถึง ชื่อ Textbox ที่จะส่งค่าไป
            
            dtp_DocDate.Text = _DGV_Dis.Rows[rowClickDis].Cells[0].Value.ToString(); //ตรงนี้เป็นการเอาในดาต้ากริดไปใส่textbox ถ้าเกิดตรง Cell[Index] ตามช่องจะข้ามและเกินไม่ได้นะครับ
            dtp_DocDate.Text = _DGV_Dis.Rows[rowClickDis].Cells[1].Value.ToString();

}