การเขียนโปรแกรมที่มี User ใช้ หลาย ๆ คน นั้น อยากทราบแนวทางในการเขียนครับว่าควรคำนึงถึงอะไรบ้างครับ

Public Class usrCtrSales3

    Private bsSales As New BindingSource 'เก็บข้อมูลรายละเอียดการขาย (Item1, Item2, Item3, ...)

    Private Sub usrCtrProduct_Load(sender As Object, e As EventArgs) Handles Me.Load
        dgvSaleItems.Columns(2).HeaderCell.Style.Alignment = DataGridViewContentAlignment.MiddleRight
        dgvSaleItems.Columns(3).HeaderCell.Style.Alignment = DataGridViewContentAlignment.MiddleRight
        dgvSaleItems.Columns(4).HeaderCell.Style.Alignment = DataGridViewContentAlignment.MiddleRight
        dgvSaleItems.Columns(5).HeaderCell.Style.Alignment = DataGridViewContentAlignment.MiddleRight
        Call MakeDataTableDEMO_Data()
    End Sub
    Private Sub MakeDataTableDEMO_Data()
        Dim dtSales As New DataTable
        dtSales.Columns.Add("Part_NO", GetType(String))
        dtSales.Columns.Add("Part_Desc", GetType(String))
        dtSales.Columns.Add("xQTY", GetType(Double))
        dtSales.Columns.Add("xPrice", GetType(Double))
        dtSales.Columns.Add("xTotal", GetType(Double))
        dtSales.Columns.Add("xDiscount", GetType(Double))

        dtSales.Rows.Add(New Object() {"P-001", "สินค้าตัวอย่าง1", 2, 50, 100, 0})
        dtSales.Rows.Add(New Object() {"P-002", "สินค้าตัวอย่าง2", 5, 30, 150, 0})
        dtSales.Rows.Add(New Object() {"P-003", "สินค้าตัวอย่าง3", 4, 6, 24, 0})

        dtSales.AcceptChanges() 'Commit Change.

        bsSales.DataSource = dtSales

        SetDGVInfo(bsSales)
    End Sub
    Private Sub SetDGVInfo(ByVal bs As BindingSource)
        dgvSaleItems.AutoGenerateColumns = False
        dgvSaleItems.Columns(0).DataPropertyName = "Part_NO"
        dgvSaleItems.Columns(1).DataPropertyName = "Part_Desc"
        dgvSaleItems.Columns(2).DataPropertyName = "xQTY"
        dgvSaleItems.Columns(3).DataPropertyName = "xPrice"
        dgvSaleItems.Columns(4).DataPropertyName = "xTotal"
        dgvSaleItems.Columns(5).DataPropertyName = "xDiscount"
        dgvSaleItems.DataSource = bsSales
    End Sub
    'กลับไปก่อนหน้า
    Private Sub BacktoPanelHead()
        pnlDetail1.Visible = False
        pnlDetail2.Visible = False
        pnlHead.Visible = True
        pnlDetail2.Dock = DockStyle.Bottom
        pnlDetail1.Dock = DockStyle.Bottom
        pnlHead.Dock = DockStyle.Fill
    End Sub
    'คลิ๊กปุ่ม เพิ่มข้อมูล
    Private Sub tsbAction_Click(sender As Object, e As EventArgs) Handles tsbAdd.Click
        Actions("A")
    End Sub
    'คลิ๊กปุ่มแก้ไขข้อมูล
    Private Sub tsbEdit_Click(sender As Object, e As EventArgs) Handles tsbEdit.Click
        Actions("E")
    End Sub
    'RowState (A/E/D)
    Private Sub Actions(ByVal mode As String)
        pnlDetail1.Visible = True
        pnlDetail2.Visible = False
        pnlHead.Visible = False
        pnlDetail1.Dock = DockStyle.Fill
        pnlDetail2.Dock = DockStyle.None
        pnlHead.Dock = DockStyle.None
        lblActions.Text = If(mode = "A", "เพิ่มข้อมูล", "แก้ไขข้อมูล")
        If mode = "E" Then
            'Binding to ALL TextBox
            For i As Integer = 0 To Me.Controls.Count - 1
                'Binding To TextBox Control
                'Binding to ComboBox Control
                'and so on.
            Next
        Else 'Edit Mode
            'Reset All TextBox/ComboBox/etc...
            mduControlManager.GetAllControl(pnlDetail1, GetType(WL_Controls.usrCtrlTextBox)).ToList().ForEach(Sub(x) DirectCast(x, WL_Controls.usrCtrlTextBox).ResetValue())
            mduControlManager.GetAllControl(pnlDetail1, GetType(WL_Controls.usrCtrComboBox)).ToList().ForEach(Sub(x) DirectCast(x, WL_Controls.usrCtrComboBox).ResetValue())
        End If
    End Sub
    'กลับไปก่อนหน้า
    Private Sub tsbBack_Click(sender As Object, e As EventArgs) Handles tsbBack.Click
        'ถ้าไม่มีการใช้ BindingSource (Me.dgvSaleItems.Rows.Clear())
        BacktoPanelHead()
    End Sub
    Private Sub dgvSaleItems_EditingControlShowing(sender As Object, e As DataGridViewEditingControlShowingEventArgs) Handles dgvSaleItems.EditingControlShowing
        'TODO
        'More...
    End Sub
    Private Sub dgvSaleItems_CellValidating(sender As Object, e As DataGridViewCellValidatingEventArgs) Handles dgvSaleItems.CellValidating
        'Clear All error message.
        dgvSaleItems.Rows(e.RowIndex).ErrorText = String.Empty
        If dgvSaleItems.Rows(e.RowIndex).IsNewRow Then 'มีอยู่ 1 แถวและไม่มีอะไรเลย
            Exit Sub 'Return 'Exist Sub
        End If
        If dgvSaleItems.CurrentCell.IsInEditMode Then
            If e.ColumnIndex = 0 Then
                dgvSaleItems.Rows(e.RowIndex).Cells(1).Value = Guid.NewGuid()
                dgvSaleItems.Rows(e.RowIndex).Cells(2).Value = 1.0
                dgvSaleItems.Rows(e.RowIndex).Cells(3).Value = 200.0
                dgvSaleItems.Rows(e.RowIndex).Cells(4).Value = 200.0
                dgvSaleItems.Rows(e.RowIndex).Cells(5).Value = 0.0
            End If
        End If
        If e.ColumnIndex > 1 Then 'Column 2 is readonly (array zero base.)
            Dim newDouble As Double
            If Not Double.TryParse(If(e.FormattedValue = String.Empty, 0, e.FormattedValue.ToString()), newDouble) OrElse newDouble < 0 Then
                e.Cancel = True
                Me.dgvSaleItems.Rows(e.RowIndex).ErrorText = "ต้องป้อนเป็นตัวเลขเท่านั้น"
            End If
        End If
    End Sub
    'คำนวณ รวมเงิน = จำนวน x ราคา/หน่วย
    Private Sub dgvSaleItems_CellValidated(sender As Object, e As DataGridViewCellEventArgs) Handles dgvSaleItems.CellValidated
        If Not dgvSaleItems.CurrentRow.IsNewRow Then
            If e.ColumnIndex > 1 Then
                dgvSaleItems.Rows(e.RowIndex).Cells(4).Value = dgvSaleItems.Rows(e.RowIndex).Cells(2).Value * dgvSaleItems.Rows(e.RowIndex).Cells(3).Value
            End If
        End If
    End Sub
    Private Sub dgvSaleItems_CellMouseClickORDbClick(ByVal sender As Object, ByVal e As System.Windows.Forms.DataGridViewCellMouseEventArgs) Handles dgvSaleItems.CellMouseClick, dgvSaleItems.CellMouseDoubleClick
            Try
                If String.IsNullOrEmpty(dgvSaleItems.Rows(e.RowIndex).Cells(0).Value) Then
                    dgvSaleItems.CurrentCell = dgvSaleItems(0, e.RowIndex)
                    Return
                End If
                Dim col As Short = dgvSaleItems.CurrentCell.ColumnIndex
                If dgvSaleItems.Columns(col).Visible = False OrElse dgvSaleItems.Columns(col).ReadOnly = True OrElse dgvSaleItems.Columns(col).CellType.ToString = "System.Windows.Forms.DataGridViewImageCell" Then
                    For iSub As Short = col To dgvSaleItems.ColumnCount - 1
                        col = (col + 1) Mod dgvSaleItems.ColumnCount
                        If dgvSaleItems.Columns(col).Visible = True AndAlso dgvSaleItems.Columns(col).ReadOnly = False AndAlso _
                            dgvSaleItems.Columns(col).CellType.ToString <> "System.Windows.Forms.DataGridViewImageCell" Then
                            Exit For
                        End If
                    Next
                End If
                dgvSaleItems.CurrentCell = dgvSaleItems.CurrentRow.Cells(col)
            Catch ex As Exception
                'log hear.
            End Try
    End Sub
    '
    'ถ้าอยู่ใน EditMode มันจะไม่เข้ามาที่อีเวนต์นี้
    Private Sub dgvSaleItems_KeyDown(sender As Object, e As KeyEventArgs) Handles dgvSaleItems.KeyDown
        If dgvSaleItems.CurrentCell.ColumnIndex = 0 AndAlso e.KeyCode = Keys.Right Then
            e.Handled = True
            dgvSaleItems.CurrentCell = dgvSaleItems(2, dgvSaleItems.CurrentCell.RowIndex)
        End If
        If dgvSaleItems.CurrentCell.ColumnIndex = 2 AndAlso e.KeyCode = Keys.Left Then           
            e.Handled = True
            dgvSaleItems.CurrentCell = dgvSaleItems(0, dgvSaleItems.CurrentCell.RowIndex)
        End If
        If dgvSaleItems.CurrentCell.ColumnIndex > 1 AndAlso (e.KeyCode = Keys.Down OrElse e.KeyCode = Keys.Enter) Then
            e.Handled = True
            If dgvSaleItems.CurrentCell.RowIndex + 2 >= dgvSaleItems.Rows.Count Then
                dgvSaleItems.CurrentCell = dgvSaleItems(0, dgvSaleItems.Rows.Count - 1)
            Else
                If dgvSaleItems.CurrentCell.ColumnIndex = 5 Then
                    dgvSaleItems.CurrentCell = dgvSaleItems.Rows(dgvSaleItems.CurrentCell.RowIndex).Cells(0)
                Else
                    dgvSaleItems.CurrentCell = dgvSaleItems.Rows(dgvSaleItems.CurrentCell.RowIndex).Cells(dgvSaleItems.CurrentCell.ColumnIndex + 1)
                End If
            End If
        End If
    End Sub

    'แสดงลำดับที่ของแถว 1, 2, 3, ...
    '
    Private Sub dgvSaleItems_RowPostPaint(ByVal sender As Object, ByVal e As System.Windows.Forms.DataGridViewRowPostPaintEventArgs) Handles dgvSaleItems.RowPostPaint
        Try
            Dim length As String = dgvSaleItems.RowCount.ToString.Length
            Dim row As String = (e.RowIndex + 1).ToString.PadLeft(length, " ")
            Dim size As SizeF = e.Graphics.MeasureString("ก", Me.Font)
            Using b As SolidBrush = New SolidBrush(dgvSaleItems.RowHeadersDefaultCellStyle.ForeColor)            
                e.Graphics.DrawString(row, dgvSaleItems.DefaultCellStyle.Font, b, e.RowBounds.Location.X + ((dgvSaleItems.RowHeadersWidth - size.Width) / 2) + 1, e.RowBounds.Location.Y + ((e.RowBounds.Height - size.Height) / 2))
            End Using
        Catch
            'logger error.
        End Try
    End Sub
    'ทดสอบการลบข้อมูลโดยการ Double Click ณ. หัวแถวนั้นฯ (ทดสอบ)
    Private Sub dgvSaleItems_RowHeaderMouseDoubleClick(sender As Object, e As DataGridViewCellMouseEventArgs) Handles dgvSaleItems.RowHeaderMouseDoubleClick
        If bsSales.Position <> -1 Then
            DirectCast(bsSales.DataSource, DataTable).Rows(bsSales.Position).Delete() 'By Ref
        End If
    End Sub
    'ตรวจสอบ RowState (FoxPro ทำได้ตั้งแต่ 20 ปีที่แล้ว ทั้ง Field State และ Row State)
    Private Sub btnGetRowState_Click(sender As Object, e As EventArgs) Handles btnGetRowState.Click
        Dim dt = DirectCast(bsSales.DataSource, DataTable)
        If dt IsNot Nothing Then
            Dim rowStateDeleted = dt.GetChanges(DataRowState.Deleted)
            Dim rowStateModifyed = dt.GetChanges(DataRowState.Modified)
            Dim rowStateAdded = dt.GetChanges(DataRowState.Added)

            'F9 Break 
            If "ขนขึ้น" <> "หอยไม่ขึ้น" Then

            End If
        End If
    End Sub
End Class

Imports System.Windows.Forms
Public Class myTextBoxColumn : Inherits System.Windows.Forms.DataGridViewColumn
    Private mAllowDecimal As Boolean
    Private mAllowMinus As Boolean
    Private mAllowDateSep As Boolean
    Private mAllowInputType As String
    Private mMaxInputlength As Integer
    Private mCelltemplate As myTextBoxCell

#Region "Properties"
    Public Property AllowInputType As String
        Get
            Return mAllowInputType
        End Get
        Set(value As String)
            mAllowInputType = value
            mCelltemplate.AllowInputType = value
        End Set
    End Property

    Public Property AllowDecimal() As Boolean
        Get
            Return mAllowDecimal
        End Get
        Set(ByVal value As Boolean)
            mAllowDecimal = value
            mCelltemplate.AllowDecimal = value
        End Set
    End Property

    Public Property AllowMinus() As Boolean
        Get
            Return mAllowMinus
        End Get
        Set(ByVal value As Boolean)
            mAllowMinus = value
            mCelltemplate.AllowMinus = value
        End Set
    End Property

    Public Property AllowDateSep() As Boolean
        Get
            Return mAllowDateSep
        End Get
        Set(ByVal value As Boolean)
            mAllowDateSep = value
            mCelltemplate.AllowDateSep = value
        End Set
    End Property

    Public Property MaxInputLength() As Integer
        Get
            Return mMaxInputlength
        End Get
        Set(ByVal value As Integer)
            mMaxInputlength = value
            mCelltemplate.MaxInputLength = value
        End Set
    End Property
#End Region

    Public Sub New()
        MyBase.New(New myTextBoxCell)
        mCelltemplate = MyBase.CellTemplate
    End Sub
    Public Sub New(ByVal dec As Boolean, ByVal min As Boolean, ByVal sep As Boolean, ByVal len As Integer, ByVal inputType As String)
        MyBase.New(New myTextBoxCell(dec, min, sep, len, inputType))
        mCelltemplate = MyBase.CellTemplate
        Me.mAllowDecimal = dec
        Me.mAllowMinus = min
        Me.mAllowDateSep = sep
        Me.mMaxInputlength = len
        Me.mAllowInputType = inputType
    End Sub
    Public Overrides Property CellTemplate() As DataGridViewCell
        Get
            Return MyBase.CellTemplate
        End Get
        Set(ByVal value As DataGridViewCell)
            MyBase.CellTemplate = value
        End Set
    End Property

    ''' <summary>
    ''' Fixed Bug Design time. lose value
    ''' </summary>
    ''' <returns></returns>
    ''' <remarks></remarks>
    Public Overrides Function Clone() As Object
        Dim myClone As myTextBoxColumn = CType(MyBase.Clone, myTextBoxColumn)
        myClone.AllowDecimal = AllowDecimal
        myClone.AllowMinus = AllowMinus
        myClone.AllowDateSep = AllowDateSep
        myClone.MaxInputLength = MaxInputLength
        myClone.AllowInputType = AllowInputType
        Return myClone
    End Function
End Class

Imports System.Windows.Forms
Public Class myTextBoxEditingControl : Inherits DataGridViewTextBoxEditingControl
    Private Const mDec As Char = "."
    Private Const mMinus As Char = "-"c
    Private Const mDateSep As Char = "/"c
    Private mAllowDecimal As Boolean
    Private mAllowMinus As Boolean
    Private mAllowDateSep As Boolean
    Private mMaxInputlength As Integer
    Private mAllowInputType As String

#Region "Properties"
    Public Property AllowInputType() As String
        Get
            Return mAllowInputType
        End Get
        Set(ByVal value As String)
            mAllowInputType = value
        End Set
    End Property
    Public Property AllowDecimal() As Boolean
        Get
            Return mAllowDecimal
        End Get
        Set(ByVal value As Boolean)
            mAllowDecimal = value
        End Set
    End Property

    Public Property AllowMinus() As Boolean
        Get
            Return mAllowMinus
        End Get
        Set(ByVal value As Boolean)
            mAllowMinus = value
        End Set
    End Property

    Public Property AllowDateSep() As Boolean
        Get
            Return mAllowDateSep
        End Get
        Set(ByVal value As Boolean)
            mAllowDateSep = value
        End Set
    End Property

    Public Property MaxInputLength() As Integer
        Get
            Return mMaxInputlength
        End Get
        Set(ByVal value As Integer)
            mMaxInputlength = value
        End Set
    End Property
#End Region

    Public Sub New()
        MyBase.New()
    End Sub
    Public Sub New(ByVal dec As Boolean, ByVal min As Boolean, ByVal sla As Boolean, ByVal len As Integer, ByVal inputType As String)
        MyBase.New()
        mAllowDecimal = dec
        mAllowMinus = min
        mAllowDateSep = sla
        mMaxInputlength = len
        mAllowInputType = inputType
    End Sub

    Protected Overrides Sub OnKeyPress(ByVal e As System.Windows.Forms.KeyPressEventArgs)
        Select Case AllowInputType.ToLower()
            Case "integer"
                If e.KeyChar < "0" Or e.KeyChar > "9" Then
                    If AscW(e.KeyChar) = Keys.Back Then    'Backspace
                        e.Handled = False
                    Else
                        e.Handled = True
                    End If
                Else
                    MyBase.OnKeyPress(e)
                End If
            Case "double"
                If e.KeyChar < "0" Or e.KeyChar > "9" Then
                    If AscW(e.KeyChar) = Keys.Back Then
                        e.Handled = False
                    Else
                        If e.KeyChar = "." And MyBase.Text.Contains(".") = False Then
                            e.Handled = False
                        ElseIf e.KeyChar = "-" And MyBase.Text.Contains("-") = False Then
                            e.Handled = False
                        Else
                            e.Handled = True
                        End If
                    End If
                Else
                    MyBase.OnKeyPress(e)
                End If
        End Select
    End Sub
    Protected Overrides Sub OnKeyDown(ByVal e As System.Windows.Forms.KeyEventArgs)
        If Me.Text.Length >= mMaxInputlength Then
            e.Handled = True
        Else
            MyBase.OnKeyDown(e)
        End If
    End Sub
End Class

Imports System.Windows.Forms
Public Class myTextBoxEditingControl : Inherits DataGridViewTextBoxEditingControl
    Private Const mDec As Char = "."
    Private Const mMinus As Char = "-"c
    Private Const mDateSep As Char = "/"c
    Private mAllowDecimal As Boolean
    Private mAllowMinus As Boolean
    Private mAllowDateSep As Boolean
    Private mMaxInputlength As Integer
    Private mAllowInputType As String

#Region "Properties"
    Public Property AllowInputType() As String
        Get
            Return mAllowInputType
        End Get
        Set(ByVal value As String)
            mAllowInputType = value
        End Set
    End Property
    Public Property AllowDecimal() As Boolean
        Get
            Return mAllowDecimal
        End Get
        Set(ByVal value As Boolean)
            mAllowDecimal = value
        End Set
    End Property

    Public Property AllowMinus() As Boolean
        Get
            Return mAllowMinus
        End Get
        Set(ByVal value As Boolean)
            mAllowMinus = value
        End Set
    End Property

    Public Property AllowDateSep() As Boolean
        Get
            Return mAllowDateSep
        End Get
        Set(ByVal value As Boolean)
            mAllowDateSep = value
        End Set
    End Property

    Public Property MaxInputLength() As Integer
        Get
            Return mMaxInputlength
        End Get
        Set(ByVal value As Integer)
            mMaxInputlength = value
        End Set
    End Property
#End Region

    Public Sub New()
        MyBase.New()
    End Sub
    Public Sub New(ByVal dec As Boolean, ByVal min As Boolean, ByVal sla As Boolean, ByVal len As Integer, ByVal inputType As String)
        MyBase.New()
        mAllowDecimal = dec
        mAllowMinus = min
        mAllowDateSep = sla
        mMaxInputlength = len
        mAllowInputType = inputType
    End Sub

    Protected Overrides Sub OnKeyPress(ByVal e As System.Windows.Forms.KeyPressEventArgs)
        'If e.KeyChar < "0"c OrElse e.KeyChar > "9"c Then
        '    If e.KeyChar <> Convert.ToChar(System.Windows.Forms.Keys.Back) Then
        '        If mAllowDecimal AndAlso e.KeyChar = mDec _
        '          OrElse mAllowMinus AndAlso e.KeyChar = mMinus _
        '          OrElse mAllowDateSep AndAlso e.KeyChar = mDateSep Then
        '            MyBase.OnKeyPress(e)
        '        Else
        '            e.Handled = True
        '        End If
        '    Else
        '        MyBase.OnKeyPress(e)
        '    End If
        'Else
        '    MyBase.OnKeyPress(e)
        'End If
        Select Case AllowInputType.ToLower()
            Case "integer"
                If e.KeyChar < "0" Or e.KeyChar > "9" Then
                    If AscW(e.KeyChar) = Keys.Back Then    'Backspace
                        e.Handled = False
                    Else
                        e.Handled = True
                    End If
                Else
                    MyBase.OnKeyPress(e)
                End If
            Case "double"
                If e.KeyChar < "0" Or e.KeyChar > "9" Then
                    If AscW(e.KeyChar) = Keys.Back Then
                        e.Handled = False
                    Else
                        If e.KeyChar = "." And MyBase.Text.Contains(".") = False Then
                            e.Handled = False
                        ElseIf e.KeyChar = "-" And MyBase.Text.Contains("-") = False Then
                            e.Handled = False
                        Else
                            e.Handled = True
                        End If
                    End If
                Else
                    MyBase.OnKeyPress(e)
                End If
        End Select
    End Sub
    Protected Overrides Sub OnKeyDown(ByVal e As System.Windows.Forms.KeyEventArgs)
        If Me.Text.Length >= mMaxInputlength Then
            e.Handled = True
        Else
            MyBase.OnKeyDown(e)
        End If
    End Sub
End Class

    ''' <summary>
    ''' Fixed Bug Design time. lose value
    ''' </summary>
    ''' <returns></returns>
    ''' <remarks></remarks>
    Public Overrides Function Clone() As Object
        Dim myClone As myTextBoxColumn = CType(MyBase.Clone, myTextBoxColumn)
        myClone.AllowDecimal = AllowDecimal
        myClone.AllowMinus = AllowMinus
        myClone.AllowDateSep = AllowDateSep
        myClone.MaxInputLength = MaxInputLength
        myClone.AllowInputType = AllowInputType
        Return myClone
    End Function