如何：通过在每个 Windows 窗体各自的线程上显示该 Windows 窗体来支持 COM 互操作
可通过在 .NET Framework 消息循环上显示窗体来解决 COM 互操作性问题，可使用 Application.Run 方法来创建该消息循环。
若要使 Windows 窗体在 COM 客户端应用程序上正确工作，必须在 Windows 窗体消息循环上运行该窗体。 若要执行此操作，请使用以下方法之一：
使用 Form.ShowDialog 方法显示 Windows 窗体。 有关详细信息，请参阅 How to: Support COM Interop by Displaying a Windows Form with the ShowDialog Method。
在单独的线程上显示每个 Windows 窗体。
Visual Studio 中对此功能提供广泛支持。
另请参阅 演练：通过在每个 Windows 窗体各自的线程上显示该 Windows 窗体来支持 COM 互操作。
示例
下面的代码示例演示如何在单独的线程上显示窗体，并调用 Application.Run 方法来启动该线程上的 Windows 窗体消息泵。 若要使用此方法，必须使用 Invoke 方法，封送任何从非托管应用程序对窗体的调用。
此方法要求窗体上的每个实例通过使用其自身的消息循环在自己的线程上运行。 每个线程上运行的消息循环不能超过一个。 因此，不能更改客户端应用程序的消息循环。 但是，可修改 .NET Framework 组件以启动使用其自身的消息循环的新线程。
Imports System.Windows.Forms
Imports System.Runtime.InteropServices
<ComClass(COMForm.ClassId, COMForm.InterfaceId, COMForm.EventsId)> _
Public Class COMForm
#Region "COM GUIDs"
' These GUIDs provide the COM identity for this class
' and its COM interfaces. If you change them, existing
' clients will no longer be able to access the class.
Public Const ClassId As String = "1b49fe33-7c93-41ae-9dc7-8ac4d823286a"
Public Const InterfaceId As String = "11651e1f-6db0-4c9e-b644-dcb79e6de2f6"
Public Const EventsId As String = "7e61f977-b39d-47a6-8f34-f743c65ae3a3"
#End Region
' A creatable COM class must have a Public Sub New()
' with no parameters, otherwise, the class will not be
' registered in the COM registry and cannot be created
' via CreateObject.
Public Sub New()
MyBase.New()
End Sub
Private WithEvents frmManager As FormManager
Public Sub ShowForm1()
' Call the StartForm method by using a new instance
' of the Form1 class.
StartForm(New Form1)
End Sub
Private Sub StartForm(ByVal frm As Form)
' This procedure is used to show all forms
' that the client application requests. When the first form
' is displayed, this code will create a new message
' loop that runs on a new thread. The new form will
' be treated as the main form.
' Later forms will be shown on the same message loop.
If IsNothing(frmManager) Then
frmManager = New FormManager(frm)
Else
frmManager.ShowForm(frm)
End If
End Sub
Private Sub frmManager_MessageLoopExit() _
Handles frmManager.MessageLoopExit
'Release the reference to the frmManager object.
frmManager = Nothing
End Sub
End Class
Imports System.Runtime.InteropServices
Imports System.Threading
Imports System.Windows.Forms
<ComVisible(False)> _
Friend Class FormManager
' This class is used so that you can generically pass any
' form that you want to the delegate.
Private WithEvents appContext As ApplicationContext
Private Delegate Sub FormShowDelegate(ByVal form As Form)
Event MessageLoopExit()
Public Sub New(ByVal MainForm As Form)
Dim t As Thread
If IsNothing(appContext) Then
appContext = New ApplicationContext(MainForm)
t = New Thread(AddressOf StartMessageLoop)
t.IsBackground = True
t.SetApartmentState(ApartmentState.STA)
t.Start()
End If
End Sub
Private Sub StartMessageLoop()
' Call the Application.Run method to run the form on its own message loop.
Application.Run(appContext)
End Sub
Public Sub ShowForm(ByVal form As Form)
Dim formShow As FormShowDelegate
' Start the main form first. Otherwise, focus will stay on the
' calling form.
appContext.MainForm.Activate()
' Create a new instance of the FormShowDelegate method, and
' then invoke the delegate off the MainForm object.
formShow = New FormShowDelegate( _
AddressOf ShowFormOnMainForm_MessageLoop)
appContext.MainForm.Invoke(formShow, New Object() {form})
End Sub
Private Sub ShowFormOnMainForm_MessageLoop(ByVal form As Form)
form.Show()
End Sub
Private Sub ac_ThreadExit( _
ByVal sender As Object, _
ByVal e As System.EventArgs) _
Handles appContext.ThreadExit
appContext.MainForm.Dispose()
appContext.MainForm = Nothing
appContext.Dispose()
appContext = Nothing
RaiseEvent MessageLoopExit()
End Sub
End Class
Imports System.Windows.Forms
Public Class Form1
Inherits System.Windows.Forms.Form
Private Sub Button1_Click( _
ByVal sender As System.Object, _
ByVal e As System.EventArgs) _
Handles Button1.Click
MessageBox.Show("Clicked button")
End Sub
'Form overrides dispose to clean up the component list.
<System.Diagnostics.DebuggerNonUserCode()> _
Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
If disposing AndAlso components IsNot Nothing Then
components.Dispose()
End If
MyBase.Dispose(disposing)
End Sub
'Required by the Windows Form Designer
Private components As System.ComponentModel.IContainer
'NOTE: The following procedure is required by the Windows Form Designer
'It can be modified using the Windows Form Designer.
'Do not modify it using the code editor.
<System.Diagnostics.DebuggerStepThrough()> _
Private Sub InitializeComponent()
Me.TextBox1 = New System.Windows.Forms.TextBox
Me.TextBox2 = New System.Windows.Forms.TextBox
Me.TextBox3 = New System.Windows.Forms.TextBox
Me.Button1 = New System.Windows.Forms.Button
Me.SuspendLayout()
'
'TextBox1
'
Me.TextBox1.Location = New System.Drawing.Point(12, 12)
Me.TextBox1.Name = "TextBox1"
Me.TextBox1.Size = New System.Drawing.Size(100, 20)
Me.TextBox1.TabIndex = 0
'
'TextBox2
'
Me.TextBox2.Location = New System.Drawing.Point(12, 38)
Me.TextBox2.Name = "TextBox2"
Me.TextBox2.Size = New System.Drawing.Size(100, 20)
Me.TextBox2.TabIndex = 1
'
'TextBox3
'
Me.TextBox3.Location = New System.Drawing.Point(12, 66)
Me.TextBox3.Name = "TextBox3"
Me.TextBox3.Size = New System.Drawing.Size(100, 20)
Me.TextBox3.TabIndex = 2
'
'Button1
'
Me.Button1.Location = New System.Drawing.Point(12, 92)
Me.Button1.Name = "Button1"
Me.Button1.Size = New System.Drawing.Size(75, 23)
Me.Button1.TabIndex = 3
Me.Button1.Text = "Command"
Me.Button1.UseVisualStyleBackColor = True
'
'Form1
'
Me.AutoScaleDimensions = New System.Drawing.SizeF(6.0!, 13.0!)
Me.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font
Me.ClientSize = New System.Drawing.Size(132, 146)
Me.Controls.Add(Me.Button1)
Me.Controls.Add(Me.TextBox3)
Me.Controls.Add(Me.TextBox2)
Me.Controls.Add(Me.TextBox1)
Me.Name = "Form1"
Me.Text = "Form1"
Me.ResumeLayout(False)
Me.PerformLayout()
End Sub
Friend WithEvents TextBox1 As System.Windows.Forms.TextBox
Friend WithEvents TextBox2 As System.Windows.Forms.TextBox
Friend WithEvents TextBox3 As System.Windows.Forms.TextBox
Friend WithEvents Button1 As System.Windows.Forms.Button
End Class
编译代码
将 COMForm、 Form1和 FormManager 类型编译成名为 COMWinform.dll的程序集。 使用 Packaging an Assembly for COM中所述的一个方法来注册 COM 互操作的程序集。 现在，你可以在非托管应用程序中使用该程序集以及它对应的的类型库 (.tlb) 文件。 例如，可在 Visual Basic 6.0 可执行项目中将类型库用作引用。
