ระบบการชื้อ-ขายอ่ะค่ะ อยากรบกวนหน่อยค่ะ ด่วน!!! ค่ะ มานอยากมากค่ะ นู้ทามไม่ได้อ่ะค่ะ

 Dim a, t, b, c As Integer
        For a = 0 To ListView1.SelectedItems.Count - 1
            Dim lvi1 As ListViewItem
            lvi1 = ListView1.SelectedItems(a)
            t = ListView1.SelectedItems(a).SubItems(4).Text
        Next

        Dim i As Integer = 0
        For i = 0 To ListView1.SelectedItems.Count - 1
            Dim lvi As ListViewItem
            lvi = ListView1.SelectedItems(i)
            ListView1.Items.Remove(lvi)
        Next

        textbox12.Text = textbox12.Text - ((t * 7) / 100)
        TextBox9.Text = TextBox9.Text - (t + textbox12.Text)


        For b = 0 To ListView1.SelectedItems.Count - 1
            c = c + ListView1.Items(b).SubItems(4).Text
        Next
        MsgBox(c)

Private Function UpdProductMinus(ByVal ProductId As String, ByVal Unitprice As Integer) As Boolean
        Dim sqlAdd As String
        sqlAdd = "UPDATE tblProduct "
        sqlAdd &= " SET UnitInstock = UnitInstock - " & Unitprice & ""
        sqlAdd &= " WHERE Product_ID = '" & ProductId & "'"
        Try
            With conn
                If .State = ConnectionState.Open Then .Close()
                .ConnectionString = strConn
                .Open()
            End With

            comBookType = New OleDbCommand
            With comBookType
                .CommandType = CommandType.Text
                .CommandText = sqlAdd
                .Connection = conn
                .ExecuteNonQuery()
            End With
        Catch
            MessageBox.Show("คุณป้อนรายการสั่งซื้อซั้า !!! ", "ข้อผิดพลาด", MessageBoxButtons.OK, MessageBoxIcon.Error)
            Return False
        End Try
        Return True
    End Function

Dim i As Integer = 0
For i = 0 To ListView1.SelectedItems.Count - 1
Dim lvi As ListViewItem
lvi = ListView1.SelectedItems(i)
ListView1.Items.Remove(lvi)
Next