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 Interop

项目
08/18/2008

更新：2007 年 11 月

可通过在 .NET Framework 消息循环（它可通过使用 Application.Run 方法来创建）上显示窗体来解决 COM 互操作性问题。

若要使 Windows 窗体在 COM 客户端应用程序中正常工作，必须在 Windows 窗体消息循环上运行该窗体。若要实现这一点，请使用下列方法之一：

使用 Form.ShowDialog 方法显示 Windows 窗体。有关更多信息，请参见如何：通过使用 ShowDialog 方法显示 Windows 窗体来支持 COM Interop。
在单独的线程上显示每个 Windows 窗体。
在 .NET Framework 组件的新线程上创建一个共享的消息循环。有关更多信息，请参见如何：通过在共享线程上显示 Windows 窗体来支持 COM Interop。

Visual Studio 中对此功能提供了广泛的支持。

演练：在每个 Windows 窗体各自的线程上显示该 Windows 窗体自身以支持 COM Interop
演练：在每个 Windows 窗体各自的线程上显示该 Windows 窗体自身以支持 COM Interop
演练：在每个 Windows 窗体各自的线程上显示该 Windows 窗体自身以支持 COM Interop
演练：在每个 Windows 窗体各自的线程上显示该 Windows 窗体自身以支持 COM 互操作
 演练：在每个 Windows 窗体各自的线程上显示该 Windows 窗体自身以支持 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，以及如何调用 Application.Run 方法在该线程上启动 Windows 窗体消息泵。若要使用此方法，必须通过使用 <codeEntityReference autoUpgrade="true">M:System.Windows.Forms.Control.Invoke(System.Delegate)</codeEntityReference> 方法，从非托管应用程序封送对窗体的任何调用。

此方法要求让窗体的每个实例都使用各自的消息循环，从而让它们在各自的线程上运行。一个线程上不能运行多个消息循环。因此，不能更改客户端应用程序的消息循环。但是，可以修改 .NET Framework 组件以启动使用其各自消息循环的新线程。

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 类型编译为称为 COMWinform.dll 的程序集。通过使用将 COM 的程序集打包中描述的一个方法，注册 COM 互操作的程序集。现在，可以在非托管应用程序中使用程序集及其相应的类型库 (.tlb) 文件。例如，可以在 Visual Basic 6.0 可执行文件项目中将该类型库作为引用使用。