无法在跨线程操作 VB.NET 中附加 RichTextBox 文本

Question

我正在编写一个多线程 TCP 回显服务器，但问题是当我从 ClientHandler 类调用 UpdateMessage 时，RichTextBox 的文本没有附加。

这是包含 RichTextBox1 的 Form1 类

公开课表1

Const PORT As Integer = 1234 'The port number on which the server will listen for connection.
Dim ServerSocket As New TcpListener(PORT) 'The Server Socket that will listen for connections on specified port number.

Dim Link As TcpClient 'The Socket that will handle the client.

Dim NumberOfClients As Integer = 0 'The total number of clients connected to the server.


Dim myThread As Thread 'The thread on which the server will handle the client


Dim sc As SynchronizationContext = SynchronizationContext.Current

Public Clienthandler As ClientHandler

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles btnStart.Click
    ServerSocket.Start()
    ' UpdateMessage("Server started..")


    myThread = New Thread(AddressOf AcceptClients) 'Handle the client in a different thread
    myThread.Start()


    btnStart.Text = "Started!"
    btnStart.Enabled = False

End Sub




Private Sub AcceptClients()


    'Keep accepting and handling the clients.
    While (True)
        Link = ServerSocket.AcceptTcpClient() 'Accept the client and let the Socket deal with it.
        NumberOfClients = NumberOfClients + 1 'update the total number of clients

        Dim ClientAddress As String = Link.Client.RemoteEndPoint.ToString

        '  UpdateMessage("Client number " & NumberOfClients & " connected from " & ClientAddress)


        Clienthandler = New ClientHandler
        Clienthandler.StartClientThread(Link, NumberOfClients)



        Me.sc.Post(AddressOf Clienthandler.UpdateMessage, "Client number " & NumberOfClients & " connected from " & ClientAddress)

    End While

    'close the sockets

    Link.Close() 'close the Socket.
    ServerSocket.Stop() 'Stop the Server Socket.

End Sub

结束类

这是 ClientHandler 类：

公共类ClientHandler

Private Link As TcpClient
Private ClientNumber As Integer
Dim NumberOfMessages As Integer = 0 'The number of messages that client has sent.
Dim Stream As NetworkStream 'The stream being used for sending/receiving data over Socket.


Dim scHandler As SynchronizationContext = SynchronizationContext.Current

Public Sub StartClientThread(Link As TcpClient, ClientNumber As Integer)

    'Initialize the class variables with the arguments passed in StartClient 

    Me.Link = Link
    Me.ClientNumber = ClientNumber



    'Start the thread

    Dim ClientThread As New Thread(AddressOf Chat)
    ClientThread.Start()

    UpdateMessage("Thread for client " & ClientNumber & " started!")



End Sub

Public Sub UpdateMessage2(消息作为字符串)

    Me.scHandler.Post(AddressOf UpdateMessage2, Message)
End Sub
Public Sub UpdateMessage(Message As String)

    Message = vbNewLine & Trim(Message)

    If Message.Length < 1 Then
        Message = "empty"
    End If

    MessageBox.Show("Updating message!" & vbNewLine & Message)


    Form1.RichTextBox1.AppendText(Message)





End Sub

同样的问题仍然存在，RichTextBox 仅从 UI 线程更新。

Answer 1

比 Hans Passant 更具体一点，在预期对象的地方使用表单名称会使用表单的默认实例，这是系统为您创建和管理的实例。默认实例是特定于线程的，这意味着每个线程有一个默认实例。如果您在辅助线程中使用默认实例，那么您使用的对象与您在 UI 线程上显示的对象不同。您可以在这里阅读更多关于默认实例的信息：

http://jmcilhinney.blogspot.com.au/2009/07/vbnet-default-form-instances.html

您需要以某种方式将方法调用编组回 UI 线程，然后更新该线程上的现有表单实例。有几种方法可以做到：

1. 可以访问现有的表单对象并调用其 Invoke 方法。
2. 使用SynchronizationContext 类将方法调用编组到 UI 线程，然后使用默认实例。

Answer 2

Class myClass
    Friend TB As TextBox
    Class myThread
        ' ...
    End Class
End Class

Class Form1
    Overrides Sub OnLoad
        _tcpClient = New myClass
        Controls.Add(_tcpClient.TB)
        _tcpClient.doSomething()
    End Sub
End Class

就像我的 cmets 所说的那样。