本实例利用Paint方法添加一个下拉框到DataGrid1上

1、新建一个Visual Basic Project 。
2、添加一个DataGrid control到窗体上。
3、加入以下代码

Imports System.Data.SqlClient

Public Class Form1

    Inherits System.Windows.Forms.Form

#Region " Windows 窗体设计器生成的代码 "

    Public Sub New()

        MyBase.New()

        '该调用是 Windows 窗体设计器所必需的。

        InitializeComponent()

        '在 InitializeComponent() 调用之后添加任何初始化

    End Sub

    '窗体重写处置以清理组件列表。

    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)

        If disposing Then

            If Not (components Is Nothing) Then

                components.Dispose()

            End If

        End If

        MyBase.Dispose(disposing)

    End Sub

    'Windows 窗体设计器所必需的

    Private components As System.ComponentModel.IContainer

    '注意：以下过程是 Windows 窗体设计器所必需的

    '可以使用 Windows 窗体设计器修改此过程。

    '不要使用代码编辑器修改它。

    Friend WithEvents DataGrid1 As System.Windows.Forms.DataGrid

    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()

        Me.DataGrid1 = New System.Windows.Forms.DataGrid()

        CType(Me.DataGrid1, System.ComponentModel.ISupportInitialize).BeginInit()

        Me.SuspendLayout()

        '

        'DataGrid1

        '

        Me.DataGrid1.DataMember = ""

        Me.DataGrid1.HeaderForeColor = System.Drawing.SystemColors.ControlText

        Me.DataGrid1.Location = New System.Drawing.Point(72, 56)

        Me.DataGrid1.Name = "DataGrid1"

        Me.DataGrid1.Size = New System.Drawing.Size(416, 184)

        Me.DataGrid1.TabIndex = 0

        '

        'Form1

        '

        Me.AutoScaleBaseSize = New System.Drawing.Size(6, 14)

        Me.ClientSize = New System.Drawing.Size(552, 285)

        Me.Controls.AddRange(New System.Windows.Forms.Control() {Me.DataGrid1})

        Me.Name = "Form1"

        Me.Text = "Form1"

        CType(Me.DataGrid1, System.ComponentModel.ISupportInitialize).EndInit()

        Me.ResumeLayout(False)

    End Sub

#End Region

    Public MyCombo As New ComboBox()

    Dim con As New SqlConnection("server=lihg;uid=sa;pwd=sa;database=northwind")

    Dim daEmp As New SqlDataAdapter("Select * From Employees", con)

    Public ds As New DataSet()

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        AddHandler MyCombo.TextChanged, AddressOf Ctrls_TextChanged

        'Fill ComboBox list.

        MyCombo.Name = "MyCombo"

        MyCombo.Visible = False

        MyCombo.Items.Clear()

        MyCombo.Items.Add("Sales Representative")

        MyCombo.Items.Add("Inside Sales Coordinator")

        MyCombo.Items.Add("Vice President, Sales")

        MyCombo.Items.Add("Sales Manager")

        MyCombo.Items.Add("Flunky")

        daEmp.Fill(ds, "Employees")

        'Set the RowHeight of the DataGrid to the height of the ComboBox.

        DataGrid1.PreferredRowHeight = MyCombo.Height

        DataGrid1.DataSource = ds

        DataGrid1.DataMember = "Employees"

        'Add ComboBox to the Control collection of the DataGrid.

        DataGrid1.Controls.Add(MyCombo)

    End Sub

    Private Sub DataGrid1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles DataGrid1.Paint

        If DataGrid1.CurrentCell.ColumnNumber = 3 Then

            MyCombo.Width = DataGrid1.GetCurrentCellBounds.Width

        End If

    End Sub

    Private Sub Ctrls_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs)

        If DataGrid1.CurrentCell.ColumnNumber = 3 Then

            MyCombo.Visible = False

            If DataGrid1.Item(DataGrid1.CurrentCell) & "" = "" Then

                SendKeys.Send("*")

            End If

            DataGrid1.Item(DataGrid1.CurrentCell) = MyCombo.Text

        End If

    End Sub

    Private Sub DataGrid1_CurrentCellChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles DataGrid1.CurrentCellChanged

        If DataGrid1.CurrentCell.ColumnNumber = 3 Then

            MyCombo.Visible = False

            MyCombo.Width = 0

            MyCombo.Left = DataGrid1.GetCurrentCellBounds.Left

            MyCombo.Top = DataGrid1.GetCurrentCellBounds.Top

            MyCombo.Text = DataGrid1.Item(DataGrid1.CurrentCell) & ""

            MyCombo.Visible = True

        Else

            MyCombo.Visible = False

            MyCombo.Width = 0

        End If

    End Sub

    Private Sub DataGrid1_Scroll(ByVal sender As Object, ByVal e As System.EventArgs) Handles DataGrid1.Scroll

        MyCombo.Visible = False

        MyCombo.Width = 0

    End Sub

    Private Sub DataGrid1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles DataGrid1.Click

        MyCombo.Visible = False

        MyCombo.Width = 0

    End Sub

End Class

4、修连接字符串Dim con As New SqlConnection("server=lihg;uid=sa;pwd=sa;database=northwind")，使能连接上数据库
5、F5运行