Thread Do Not Resume When The Delegate Returns?
Jun 2, 2010
It seems that there is a glitch in Vb, While having some tasks ( Thread ) queued using Tasks if you try to use Invoke, the thread do not resume when the delegate returns.If BeginInvoke is used, it works but the problem is that it become impossible to execute a delegate synchronously.This does force the use of the AutoResetEvent to control the thread.The problem comes when the thread execute some code in a other classes, using a single AutoResetEvent within many classes just give a very dirty 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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Jun 22, 2010
I have a a main thread and another background thread that does some work (see below).I want to do something within my worker thread and then wait until some other event happens in the main thread before continuing. How do I do this? I thought I could use ManualResetEvent but I can't get it to work properly. I'm a bit confused about the Set, Reset, WaitOne methods and where exactly I should call them from.When the worker thread is suspended it shouldn't affect the main thread.
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System. EventArgs) Handles MyBase.Load
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
[code]....
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Jun 3, 2012
Looking for a solution to pause and resume a thread. When I use suspend and resume it says its no longer supported. Here is the code. I'm just trying to get it to cycle between two "do until" events.
[Code]...
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Oct 6, 2011
I have a thread running on my application that checks a database every so often to decide whether or not to update nodes in a treeview.
Each treeview node represents a document and I have an open button that opens the document for the user.
When the document is opened, I wanted to suspend the thread that refreshes the node list until the document is closed.
I have MyThread.Suspend and MyThread.Resume. But the document viewer is on another thread.
I created functions for suspending/resuming the thread in the application. I have delegates in the viewer to call those functions from another thread. But I'm still getting an Error. "Thread is not user-suspended. Cannot be resumed" or something of the like.
But I realize that Suspend and resume are obsolete functions, so what class or objects should I be looking into and if it didn't take up too much of your time, a small example as well?
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Dec 4, 2008
A non-UI thread in my prog needs to obtain data from a UI listview control. To prevent cross-thread errors I use the following, but it freezes the prog (probably because the "Else" part is never called).What am I doing wrong?
[Code]...
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Jun 10, 2011
So, I'm having troubles implementing a separate thread. This is because I have a simple class, and in it I start a new thread. So, as it is not any form, I haven't found any way to make it call the function in the UI Thread.
So, I cannot use the Invoke method. Is there any way to call a function from another thread?
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Aug 5, 2009
I have a GUI which executes on the GUI-thread. Further I have another thrad which does video processing using DirectShow (this is COM).
- Now I want to execute a function on the same thread as where the videoprocessing is executing. This is initiated by the GUI-thread. Touching the COM-referenced object goes wrong if a execute the function from another thread (I understand that). When a call the function from the same thread everything goes fine. But to do this I have the poll some flag-bits in the mainloop, and that is not a 'pretty' solution...
All discussions on the internet are about how change the GUI from a different thread.
I have tried several things:
1) Invoke the function using a delegate. This doesn't wordt, since the function is executed in the GUI thread. (checked bu ThreadID's)
2) BeginInvoke the function using a delegate. May be .net executes the function in a original thread where the object has been created. This does also not work: .net used random threads (probaby from the threadpool)
3) ISynchronizeInvoke, Threading.SynchronizationContext and some other features seems only to work on the GUI thread only...
The question: Is there a way to Post, Send of Invoke a delegate on the specific thread (for example by a reference to this thread or threadID)
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Mar 3, 2012
i have a background thread when it is done doing its task it notifies the main thread via a delegate sub it seems if the main thread is "busy" then the background thread hangs waiting for the main thread. if this is normal, which i assume it is my background thread, starts another thread, and this 2nd background thread makes the delegate call is this bad practice?
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Feb 1, 2010
Disclaimer: I know that Thread.Abort is evil. I'm using it as a last resort since some I/O functions (e.g., File.Exists when used on a non-existing network share) block for a large amout of time and do not allow you to specify a timeout.
Question: Is it possible to Abort (as in Thread.Abort) a worker thread started using Delegate.BeginInvoke or do I have to do the Thread handling myself?
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Oct 4, 2010
What is the Invoke syntax to marshall data from a background thread receive callback method to a function on the UI Thread?(Form1).
Public Class Form1
MyDelegate = New DisplayData(AddressOf DisplayData)
Private Sub Form1_Load()
MyDelegate = New DisplayData(AddressOf DisplayData)
[code]....
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Jan 30, 2010
from the documentation we have this: Multicast Delegate: Represents a multicast delegate; that is, a delegate that can have more than one element in its invocation list.
so am i right to say that Multicast delegate is no different from a normal delegate other than the fact that it has arguments. so System.Action is a 'normal' delegate whereas System.Action(T)(Byval obj as T) is a multicast delegate?
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Feb 9, 2010
I've created a Delegate that I intend to call Async.
[Code]...
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Jun 1, 2010
Code:
Public Class SendPings
Shared Sub New()
AddHandler Post.Saved, AddressOf Post_Saved[code].....
I get a error" Method 'Private Shared Sub Ping(item As BlogEngine.Core.IPublishable, itemUrl As System.Uri)' does not have a signature compatible with delegate 'Delegate Sub WaitCallback(state As Object)'.
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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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Mar 23, 2010
I am trying to write a VB.NET alternative to a C# anonymous function.I wish to call Threading.SynchronizationContext.Current.Send which expects a delegate of type Threading.SendOrPostCallback to be passed to it. The background is here, but because I wish to both pass in a string to MessageBox.Show and also capture the DialogResult I need to define another delegate within. I am struggling with the VB.NET syntax, both from the traditional delegate style, and lambda functions.My go at the traditional syntax is below, but I have gut feeling it should be much simpler than this:
Private Sub CollectMesssageBoxResultFromUserAsDelegate(ByVal messageToShow As String, ByRef wasCanceled As Boolean)
wasCanceled = False
[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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Apr 7, 2010
I'm using Visual Studio 2005 (with Visual Basic) to create my own personal web site. I want to include a page that has my resume, but I don't want the format to be affected. What would be the best way to do this. I thought that possibly putting it in as an image might work, but I haven't tried that yet.
After I get this done, is there a way to add a button so a user can download my resume?
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Sep 16, 2010
Can anyone tell me how I could make my program (running in background) do something when when Windows becomes active after being idle?
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Jun 7, 2007
I have a case where I need to resume execution on the next line after an exception. Is there no way to do this using the structured error handling? I realize that I can go back to the "On Error .. Goto", but I can't believe there's not a way to do this with structured error handling...
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