ทำ textbox รับค่าผลรวมอัตโนมัติ ต้องการโค้ดให้ textbox รับค่าจาก คอลัมน์รวมเป็นเงินใน datagridview อัตโนมัติ

Imports System.Data
Imports System.Data.SqlClient
Imports System.Text
Public Class Form2
    Dim dr As SqlDataReader
    Dim cn As SqlConnection
    Dim cm As SqlCommand
    Dim sb As New StringBuilder
    Dim strSql As String
    Dim strCn As String = "Data Source=bkk314;Initial Catalog=DB_For_Webboard;Integrated Security=True"
    Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        cn = New SqlConnection()
        With cn
            If .State = ConnectionState.Open Then .Close()
            .ConnectionString = strCn '' string ที่ใช้ต่อ connection
            .Open()
        End With
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        sb.Remove(0, sb.Length) '' คำสั่ง Query ข้อมูล
        sb.Append("Select productid,productname,price,qty,totalprice,datesales From Product")
        sb.Append(" Where  (datesales Between '" & DateTimePicker1.Value.ToString("MM/dd/yyy") & "' And '" & DateTimePicker2.Value.ToString("MM/dd/yyy") & "')")
        strSql = sb.ToString() '' เก็บใน String 

        com = New SqlCommand()

        With com
            .CommandText = strSql
            .CommandType = CommandType.Text
            .Connection = cn
            dr = .ExecuteReader()
        End With
        If dr.HasRows Then ''check dr
            Dim dtSql As DataTable
            dtSql = New DataTable()
            dtSql.Load(dr)
            With DataGridView1
                .DataSource = dtSql ''**

                Dim i As Integer = 0 '' วิธีแรกครับ
                Dim SumPrice As Double = 0
                For i = 0 To DataGridView1.Rows.Count - 1
                    SumPrice += CDbl(DataGridView1.Rows(i).Cells(4).Value)
                Next
                TextBox1.Text = SumPrice.ToString("#,##0.00")
                '---------------------------------
                Dim i2 As Integer = 0 ''วิธีที่สอง
                Dim SumPrice2 As Double = 0
                For i2 = 0 To dtSql.Rows.Count - 1 ''**
                    SumPrice2 += CDbl(dtSql.Rows(i2).Item("totalprice"))
                Next
                TextBox1.Text = SumPrice2.ToString("#,##0.00")
            End With
        End If
    End Sub
End Class