Thread Communication - Return The Information Back To The UI Thread?
Feb 20, 2011
I'm using webclient to download a webpage but obviously since it's on the UI thread it freezes.How can i change my class to be multi threaded using DownloadStringAsync? i can do this normally but since i am needing to return the information back to the UI thread i am a bit stuck
Public Class RequestExecutableInformation
Public Function FileReport(ByVal executable As String, ByVal ParameterStart As String, ByVal ParameterFinish As String) As String
Dim Source As String = String.Empty[code]...
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Nov 9, 2011
in my Winforms application, there is a main thread. It is not the UI thread but it starts the UI thread. In the main thread, I'm using a Mutex to prevent the application from being started twice. That's why I'm making an exception from the rule not to use a Thread's Join method. In this case, the main thread does call UIThread.Join before releasing the Mutex. That works well.
The strange problem is: Whenever an exception occurs in the UI thread, the default Windows error dialog pops (send report, debug, close). If I select "close", the application does not quit. Instead, the main window (created in the UI thread) stays visible, but it is inoperatable. It looks as if the UI thread still does not quit, and consequently the main thread's call to UIThread.Join doesn't return either.
Though, if I debug the application at that point, the "threads" window does not show the UI thread anymore. I've given it the name "UI Thread" (surprisingly).So, why does the Join method not return even if the thread has died? Why is a window of a died thread visible?The following screenshot shows the Threads window below and the window above shows the callstack of the main thread ("Hauptthread").
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Aug 13, 2010
In one application, I need use 4 simultaneous threads.When the threads finished, I need to update the text of a TextBox.So, I create 4 Textbox, and I wanna the threads change the text to FINISHED.Each thread change one distinct TB.I use this "example"
Dim Terminados As Integer = 0
Private Sub frmEnviarMensagem_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Timer1.Enabled = True
Timer1.Start()
[code]....
The problem is, I have an error in the red lines.The error is: INVALIDOPERATIONEXCEPTION "Cross-Thread operation not valid: Control tbPlaca1 Accessed from a thread other than the thread it was created on."I don't use cross threading. Each TB only was accessed for the correspondent thread, and for the "main program".
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Nov 3, 2011
This is the error message I am getting:
"Cross-thread operation not valid: Control 'Panel1' accessed from a thread other than the thread it was created on." The reason I am getting this error is because I am opening up a new form and then calling these three things:
Panel1.Show()
Label1.Show()
Label2.Show()
why I get this error message because it doesn't occur normally if I open Form2 after closing Form1, it only occurs when I open Form2 after closing Form4.
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Jul 21, 2009
I have done a program using vb2005 to display reading from my microcontroller bs2 board but have encountered some problems. My code are as follows.
Dim Stop_Rx As Boolean
Private Sub btnRead_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnRead.Click
SerialPort1.Open()
[code]....
I've encounter an error which is, (Cross-thread operation not valid: Control 'txt1' accessed from a thread other than the thread it was created on.)
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Jun 21, 2012
When my client try to connect to server I'm getting this error : Cross-thread operation not valid: Control 'l_users' accessed from a thread other than the thread it was created on.
Private Sub _socketManager_onConnectionAccept(ByVal SocketID As String) Handles _socketManager.onConnectionAccept
l_Users.Items.Add(SocketID)
End Sub
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Feb 17, 2012
Would anyone be able to help me here please. I'm fairly new to VB.net and threading so im just trying to figure out what is happening.When I debug this I am getting the error thread operation not valid: Control 'ProgressBar1' accessed from a thread other than the thread it was created on.
I'm a little lost as to why the error is occuring or how to fix it. I've had to put the progress bar in a separate thread otherwise the GUI crashes
[Code]...
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Sep 2, 2010
My understanding is that thread.join will suspend the execution of code on the calling thread until the spawned thread finishes or is aborted...
With that in mind, I tried this:
For i = 1 to 50
threads = New Thread(AddressOf test)
threads.IsBackground = True
threads.SetApartmentState(ApartmentState.STA)
[CODE]...
However, the rest of the code runs when the loop finishes, not waiting for all the spawned threads to finish. Since the rest of the code needs the threads to finish (otherwise the rest will error).
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Jun 6, 2010
I have written an application that loads a form - frmCad as well as AutoCad. It does this via a class which detects when AutoCad quits.
Friend Class CadApp Private WithEvents AppObject As AcadApplication... Private Sub AppObject_BeginQuit(ByRef Cancel As Boolean) Handles AppObject.BeginQuit RaiseEvent Quit() End SubEnd Class
My main class loads frmCad as well as CadApp.
Public Class Cad Private WithEvents frmCad As CadForm Private WithEvents app As CadApp... Public Sub ShowForm() If frmCad Is Nothing Then frmCad = New CadForm frmCad.Visible = True End Sub... Private Sub app_Quit() Handles app.Quit frmCad.Dispose() frmCad = Nothing .... End Sub
When I debug the program, it stops at frmCad.Dispose()The program continues to execute, but all the code after it fails to work.Looking more carefully I get an error message which contains:-Cross-thread operation not valid: Control 'Autocad' accessed from a thread other than the thread it was created on.
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Feb 9, 2011
My error:Cross-thread operation not valid: Control 'label2' accessed from a thread other than the thread it was created on. I want to be able to give my Public RunBot() sub access to edit Labels, buttons, etc without an error.
[Code]...
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Apr 1, 2010
I'm getting the 'System.InvalidOperationException' error on acccessing a thread from other than where it was created. My code is:
'Required by the Windows Form Designer
Public components As System.ComponentModel.IContainer ' changed from private
[code]....
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Jun 6, 2009
My problem is Cross-thread operation not valid: Control 'statusHO' accessed from a thread other than the thread it was created on.
System.InvalidOperationException was unhandled
Message="Cross-thread operation not valid: Control 'statusHO' accessed from a thread other than the thread it was created on."
Source="System.Windows.Forms"
StackTrace:
[Code]...
i used it and it works fine then. but as it is mentioned its not a good practice to use it. So what should i do? is it ok if i use this as i am not able to use correct practice. Mine application is not for enterprise purpose. its just my class project, and it works fine even if i put application working in background. System works ok. I dont know how to correct this error.As i dont have that much knowlege of threads.
So please guide me how to fix this in correct way otherwise i am force to go for bad programming practice
Please refer to Windows Mobile Developer Center > Smart Device Development Forums > Windows Mobile Development > Appendtext not working for all my code details
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Aug 4, 2009
Cross-thread operation not valid: Control 'lv1' accessed from a thread other than the thread it was created on.
Dim lvi As ListViewItem
For Each lvi In lv1.Items
[code]....
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Feb 7, 2011
Ok i have a Form with the following
Private Sub frmMain_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
txtNotepad.Text = LoadFile("notes.txt")
[code].....
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Jan 24, 2011
I'm having some trouble getting cross-thread communication/field-updating working properly in my VB.NET 2010 program. I'm trying to update a field on my main form whenever a thread that I've started throws an event. Here's a simplified version of my code:
My main form:
Public Class Main
' stuff
' Eventually, startProcessing gets called:
[Code]....
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Dec 15, 2009
I am using a COM library in my VB.NET app that has an asynchronous execution method and signals my application via an event when it completes. The event handler is on a different thread from the calling thread. I want to invoke another execution on the main thread when I receive the completion event. If I call directly in the event handler for another execution it starts on the new thread. How do I marshal back to the main thread. This is done in a dll not in a form.
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Oct 17, 2009
I tried to make a thread (address of function) , but vb.net didn't accept that.
is there any way to return a value from a thread ?
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Sep 20, 2010
In a threadpooling situation is it possible for a modal form to be opened and data from that form to be passed back to the thread that opened it ?
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May 2, 2009
I am using a class with below code, the question is how to update the label's value at UI thread from the backgroundworker?
Imports MySql.Data.MySqlClient
Public Class clsBackGroundWorker
[code]....
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Mar 10, 2009
This is my simple code that calls a function from a class I created called "clsNetwork". The function simply pings a computer from a computername I pass it and returns the results.
Dim PingStatus As String
PingStatus = clsNetwork.PingComputer(ComputerName)
txtbox.text = PingStatus
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Sep 25, 2009
I have a Window Forms application (using clickonce installation, running on a terminal server) that occasionaly ends up with a thread that appears to be running in a tight loop. The user doesn't know this happens as the app continues to run as expected. Also I have determined that I can kill the problem thread without any apparent affect on the app.
I can use Process Explorer to find the instance of an app with the problem and can isolate the thread with the problem but haven't found any way to look into the thread to find anything that would help me determine what is causing the problem. Does anyone know of a way to some additional information about a thread, like maybe strings, that would help me zero in on the issue?
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Sep 18, 2009
When i run the program i am getting the following error in this line TextBox1.Text &= "File Created: " & FullPath & vbCrLf"Cross-thread operation not valid: Control 'TextBox1' accessed from a thread other than the thread it was created on."
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Mar 4, 2009
I'm creating a Client Server application which involves theServer running some scripts in clients and getting back results in an automated way. In Server, other than Main thread, i have 2 worker threads, a) one monitoring response from clients and b) the other scheduling next available job to respective client which executes that job. The issue here is ,I want these worker threads to write the status of their work in the UI(which comes under Main Thread). Also i need to write things in worker thread in a Data table and Rich Text Box in Main thread. But, I can't do so, since it has been blocked to access one thread's function or property directly from others. Is there any work around to do this?
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Aug 16, 2010
I have such a bad habbit of cramming all my code into one form. But i dont know when i should write a class. or dont really understand how to return the information back to form1. when should i even use a class? for example i have some code here
[Code]...
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Nov 12, 2009
Preface: I know this is an unusual/improper way to do this. I can do this with a "real" ShowDialog(), background worker/thread, and so on. I am trying to do specifically what I describe here, even if it is ugly. If this is impossible for X reason, I have created a fancy progress dialog for some of our long running operations. I need to have this dialog shown on a new thread while having processing continue on the calling (UI in most cases) thread.
[Code]...
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Sep 5, 2009
I need your help on the following. In debugging mode only the program is stopping to the following line "My.Forms.FormMain.HelpProviderMain.HelpNamespace = "Reports.chm"" with the following error ""An error occurred creating the form. See Exception.InnerException for details. The error is: Cross-thread operation not valid: Control 'FormSplash' accessed from a thread other than the thread it was created on.""
I noticed that when I am putting NONE in SPLASH screen option in the properties of the project, there is no problem.I am no familiar with treating that's why can you give me detail instruction how to overcome this annoying problem?
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Nov 14, 2009
I am getting this exception: Cross-thread operation not valid: Control 'TextBoxOutput' accessed from a thread other than the thread it was created on. in a VB 2008 Windows Forms application that I havent specifically made multi-threaded. I have create a sub called Out() like this:
Private Sub Out(ByVal inString As String)
Me.TextBoxOutput.Text += (Me.TextBoxOutput.Text & inString & vbNewLine)
Me.TextBoxOutput.SelectionStart = Me.TextBoxOutput.Text.Length
Me.TextBoxOutput.ScrollToCaret()
End Sub
and I call it from various events to log messages I am getting from my pbx, which I use a third party open source dll to access. The interesting thing to me is that if I run the deployed application (ie, not in the VS IDE) I do not get any exceptions, it's only from within the IDE.if I add the line: Control.CheckForIllegalCrossThreadCalls = False to the form's constructor, the exceptions stop, but a) this seems like a hacky way to get around the issue and b) the application seems to hang sometimes when I have it set this way.
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Sep 5, 2009
In debugging mode only the program is stopping to the following line "My.Forms.FormMain.HelpProviderMain.HelpNamespace = "Reports.chm""
with the following error ""An error occurred creating the form. See Exception.InnerException for details. The error is: Cross-thread operation not valid: Control 'FormSplash' accessed from a thread other than the thread it was created on.""I noticed that when I am putting NONE in SPLASH screen option in the properties of the project, there is no problem.
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Mar 10, 2010
im getting this error and i cant figure it out.
Public Sub mlogin()
Invoke(chkb, New Object() {"disable"})
Invoke(d, New Object() {achidrtb, "", "="})
Invoke(d, New Object() {hiddenrtb2, "", "="})
[code]....
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Aug 27, 2011
I am trying to call a method that started on a background thread on the UI thread calling BeginInvoke and passing in a delegate as follows:
Dispatcher.BeginInvoke(Function() UpdateApplicationDataUI())
to call this method:
Private Sub UpdateApplicationDataUI()
...
End Sub
However, I get an error in the call to BeginInvoke (the UpdateApplicationDataUI portion of the delegate is stating "Expression does not produce a value").
Me.Dispatcher.BeginInvoke(Function() New Action(AddressOf UpdateApplicationDataUI))
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