Is it possible to create controls from a new thread in a multithreading windows form application

[Amer Rehman 0]

Hi Here is the code that I'm working on. Imports System.Threading Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click             tcpSend = New TcpSender             Dim trSend As New Thread(AddressOf tcpSend.RetrieveData)             trSend.Name = "Data Receiver"             tcpSend.Command = "Send data"             tcpSend.SysName = "Cabin1"             tcpSend.Port = 100             trSend.Start()             End Sub Imports System.net Imports System.Net.Sockets Imports System.IO Public Class TcpSender       Public Event SystemReplied(ByVal data As String)       Public Command, SysName As String, Port As Int16       Public Sub RetrieveData()             Try                   Dim tcpCli As New TcpClient(SysName, Port)                   Dim ns As NetworkStream = tcpCli.GetStream                   Dim sw As New StreamWriter(ns)                   Dim sr As New StreamReader(ns)                   ' Send data to the client.                   sw.WriteLine(Command)                   sw.Flush()                   ' Receive and display the response.                   If Command = "Send data" Then                         Dim strResult As String                         'read the first line                         strResult = sr.ReadLine &am

[Moreno Airoldi]

You must use Invoke to call a routine which will then be in the UI thread. For example:

Dim dataStorage As String

Private Sub SystemRepliedEventHandler(ByVal data As String) Handles tcpSend.SystemReplied

    'MsgBox(data)
    'create the controls to display data
    'this doesn't work
    'Dim type As New TextBox
    'type.Location = New Point(100, 100)
    'type.Size = New Size(100, 100)
    'type.Text = data
    'Controls.Add(type)

    dataStorage = data
    Invoke(New MethodInvoker(AddressOf MyAddControl))

End Sub

Private Sub MyAddControl()

    Dim type As New TextBox
    type.Location = New Point(100, 100)
    type.Size = New Size(100, 100)
    type.Text = dataStorage
    Controls.Add(type)

End Sub

You can think of a more elegant way of passing over data and such, but basically this is what you need. It may be also interesting to consider the InvokeRequired method, which will return true if you are on a different thread than the UI. It can be useful when you need to know if you need to use Invoke. In your case it's perfectly safe to always use Invoke, but you can also change your code this way:

Private Sub SystemRepliedEventHandler(ByVal data As String) Handles tcpSend.SystemReplied

    dataStorage = data
    If (InvokeRequired) Then
        Invoke(New MethodInvoker(AddressOf MyAddControl))
    Else
        MyAddControl()
    End If

End Sub

Hope this will be of help. :)

2+2=5 for very large amounts of 2 (always loved that one hehe!)

[Dave Kreskowiak]

You cannot create controls on a seperate thread. However, your thread code can Invoke a method on the UI thread that creates the controls for it.

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Dave Kreskowiak Microsoft MVP Visual Developer - Visual Basic
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