In the gridview, I want to bind data to a textbox. How do I do that? Any help would be greatly appreciated.

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false" 
            onrowdatabound="GridView1_RowDataBound">
        <Columns>
            <asp:BoundField DataField="Id" HeaderText="Id" />
            <asp:BoundField DataField="Field1" HeaderText="Field 1" />
            <asp:TemplateField>
                <ItemTemplate>
                    <tr>
                        <td colspan="3">
                            <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
                        </td>
                    </tr>
                </ItemTemplate>
            </asp:TemplateField>
        </Columns>
     </asp:GridView>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace WebFormDemo
{
    public partial class Repeater : System.Web.UI.Page
    {

        protected void Page_Load(object sender, EventArgs e) {
            if (!IsPostBack) {
                BindGridView();
            }

        }

        private void BindGridView() {
            var data = GetSampleData();

            GridView1.DataSource = data;
            GridView1.DataBind();
        }


        private List<Student> GetSampleData() {
            List<Student> students = new List<Student>();
            students.Add(new Student() { Id = 1, Field1 = "SomeText 1", Field2 = "SomeText 1" });
            students.Add(new Student() { Id = 2, Field1 = "SomeText 2", Field2 = "SomeText 2" });
            students.Add(new Student() { Id = 3, Field1 = "SomeText 3", Field2 = "SomeText 3" });

            return students;
        }

        protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e) {
            if (e.Row.RowType == DataControlRowType.DataRow) {
                //access first column
                int id = Convert.ToInt32(e.Row.Cells[0].Text);

                //access the TexBox
                TextBox tb = (TextBox)e.Row.FindControl("TextBox1");
                tb.Text = "Assign whatever value here";
            }
        }
    }

    public class Student
    {
        public int Id { get; set; }
        public string Field1 { get; set; }
        public string Field2 { get; set; }
    }
}

Imports System
Imports System.Collections.Generic
Imports System.Linq
Imports System.Web
Imports System.Web.UI
Imports System.Web.UI.WebControls

Namespace WebFormDemo
    Public Partial Class Repeater
        Inherits System.Web.UI.Page

        Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
            If Not IsPostBack Then
                BindGridView()
            End If
        End Sub

        Private Sub BindGridView()
            Dim data = GetSampleData()
            GridView1.DataSource = data
            GridView1.DataBind()
        End Sub

        Private Function GetSampleData() As List(Of Student)
            Dim students As List(Of Student) = New List(Of Student)()
            students.Add(New Student() With {
                .Id = 1,
                .Field1 = "SomeText 1",
                .Field2 = "SomeText 1"
            })
            students.Add(New Student() With {
                .Id = 2,
                .Field1 = "SomeText 2",
                .Field2 = "SomeText 2"
            })
            students.Add(New Student() With {
                .Id = 3,
                .Field1 = "SomeText 3",
                .Field2 = "SomeText 3"
            })
            Return students
        End Function

        Protected Sub GridView1_RowDataBound(ByVal sender As Object, ByVal e As GridViewRowEventArgs)
            If e.Row.RowType = DataControlRowType.DataRow Then
                Dim id As Integer = Convert.ToInt32(e.Row.Cells(0).Text)
                Dim tb As TextBox = CType(e.Row.FindControl("TextBox1"), TextBox)
                tb.Text = "Assign whatever value here"
            End If
        End Sub
    End Class

    Public Class Student
        Public Property Id As Integer
        Public Property Field1 As String
        Public Property Field2 As String
    End Class
End Namespace