Update UI Form From Worker Thread?
Oct 20, 2010
I am new to multi-threading in VB.NET and have come across a problem whereby I am wanting to append text to a text box on a form from a service thread running in the background.
The application I am developing is a client/server listener, I have been able to get the client and server PC's to talk with each other (confirmed through MsgBox), however I am now struggling to get the service thread on the server to append the text to the textbox, nothing vissible occurs.
I have a form named testDebug which calls a class (RemoteSupport), this class does all the handshake tasks and updates the textbox with the connection data.[code]...
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Sep 4, 2009
I have a standard windows application called winap. I have a com component which acts as an api to the winap. I have a class in winap call classapi which has all the methods that the api calls and all works well. The problem is that one of the methods in my class api needs to get a handle on form elements in the main worker thread. Whenever I try to access an existing form I keep getting null because the for exists in the main worker thread and my api call is in a seperate thread.
[Code]...
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Nov 22, 2009
[code]...Update variable form background worker?
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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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Oct 31, 2010
I have a form and controls on from I work with background worker on my form and I want when I work with background worker in (for next) changed a data table example (mydt.clear()) or change a datagrideview..how to update controls on a form when we work with background worker? [code]
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May 9, 2010
I've looked at the on line doc over and over, and I can't seem to figure out why this won't work. This code runs the thread, and the thread seems to execute the code in the 'threadsafe' sub, however neither the progress bar is updated or the button click performed.
Imports System.Threading
Public Class VisNotify
Inherits Form
[Code].....
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Sep 1, 2009
I'm not sure exactly how to describe this. In VB6, there was a Timer command. I could create a variable of type Timer and loop until the current value for Timer exceeded the initial plus a given amount of time. This allowed me to update form variables while the timing loop was executing. How can I do something similar in .NET?[code]...
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Apr 22, 2012
I have a form that looks like this:and i'm using a backgroundworker to update the components:
Code:
Private Sub btnGO_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnGO.Click
[code].....
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Dec 27, 2009
I have some class that splits some work onto multiple worker threads. To be more specific: the class represents a download, that can have as many segments as the user wants, that get then put onto separate threads.When I run the download with one segment, it works fine. When I run it with 2 segments, the second segment encounters an error.[code]When I put a breakpoint on the if, it'll stop there, but when I go to the next line, I get an error.I don't get what's getting wrong, and got a headache after a few hours of attempting to keep track of the correct thread.Anyone an idea what's going wrong, or how I can detect it better? (This is the first time I'm doing real multi threading debugging.
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Oct 27, 2009
This is slightly different to just updating a UI from a worker thread. The object which calls the thread, calls another object, and it is this object which is is trying to update the UI. It doesn't however work.
Imports System.Threading
Public Class Form1
Public Delegate Sub GetText(ByVal sText As String)
Public GetSomeText As GetText
Public Sub New()
' This call is required by the Windows Form Designer.
[Code] .....
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Jun 8, 2010
I run a thread from my main form that do some stuff i want that each action that the thread do will be written on a lable on the main form. How can i do that? I try to give it a pointer of the form but with no luck since its not allowed by the compiler. here is how i create the thread object in my form:
[Code]...
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Nov 1, 2011
I've got a List(Of IWorker) which contains a number of concretes. IWorker in turn has a Startup() and Shutdown() method.Inside the Worker class, Startup() creates a new worker thread then returns. Shutdown() presently sets a private ShutDownRequested flag and returns. The flag is checked by the worker thread (at worst every few seconds).This all works fine but at present the parent app has no way to determine if the Worker has finished shutting down.I can see a number of ways around this but am not sure what the best one is.Add a State property to IWorker. Should work but I'm going to be polling states which seems a little nasty.Make the shutdown command blocking - Would probably be my ideal solution but I'm not sure how to implement it - does the worker Sunclock a private object which Shutdown() should also try to Synclock after setting the flag?
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Aug 24, 2009
Here is my setup:
Form1.vb - contains RichTextBox1 and BackgroundWorker1, which calls a the Control module.
Control.vb - calls Display module.
Display.vb - calls Form1.SetTextBoxText("text here").[code]...
My observations: When the Display module calls SetTextBoxText, InvokedRequired's is false. Also, if the BackgroundWorker1 (which is in Form1.vb) calls SetTextBoxText, it works. But if BackgroundWorker1 calls a module that calls SetTextBoxText, it doesn't work.
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Apr 6, 2012
I have a BackgroundWorkerThread which I want to use serially.So some of the code in the UI thread will look like this [code]But of course I can't do the second RunWorkerAsync until the UI thread has seen the RunWorkerCompleted event indicating that the "Sequences" work has been completed (or somehow knows that the "Sequences" work has been completed).So I need some sort of synchronization between the two RunWorkerAsync calls, but whatever I use cannot hang up the UI thread because it has to be able to handle ProgressChanged events.Maybe the RunWorkerCompleted event could make the second call but I really don't like that structure.So how do I delay the second call to RunWorkerAsync (for the "Templates" work) until the background thread has completed the "Sequences" work?
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Apr 6, 2011
I have searched the forum and found several forums related to the backgroundworker thread but have been unsuccessful in finding my answer.My objective is to display an animated gif or progress bar while the program is executing a particular method which can take upwards of several minutes to complete. I cannot get the second thread to run the progress bar while the main progrem is executing the time consuming method. I have created a demo based on another thread and can't seem to get it to create two threads. I was attempting to get the backgroundworker to execute the progress bar while my main code runs on UI thread.
[Code]...
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Apr 25, 2012
I have a application which processes 1000's datas.. for each processing it needs to update gui and db and many variables in my application. So what i have planned is to use 50~90 background worker with my own algorithm of thread pool, synchronization and thread close.So here is it efficient in terms of memory and performance. just confused what to use.. backgroundworker componenet or standard thread.
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May 30, 2011
I am testing a background workder. I am running the following code for the test.
Private Sub bgwTest_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles bgwTest.DoWork
Dim a As Integer = 0
Do While a < 10 'Infinite loop
ComboBox1.Items.Add(1)
[Code] .....
But this code generates the following error:
"Cross-thread operation not valid: Control 'ComboBox1' accessed from a thread other than the thread it was created on."
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May 19, 2010
Can someone tell me how to get the selected text in the combo as it encountered cross-thread in the following code:
[Code]...
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Nov 3, 2011
I am trying to create a new instance of a form if its not allready been created the only problem is is that the instance creation is inside a worker thread.[code]...
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Aug 6, 2010
I'm working on a web application that uses the web browser control to get and set info from my website. The content on the site is pulled from different pages and the data the application stores becomes really huge so i used a background worker to do the work and keep the form responsive. On each loop i call to get the webbrowser's inner html so i can sort through it and grab what i need and it works; but only the first time!? After i call it the first time and try to call it again to update the variables the function hangs and then the console shows me a Thread Abort Exception, The try statement i used to contain it doesn't fire off an exception. When i debug the program and i get to that function, it hangs and then just stops working.
The function that loops:
vb.net
Dim ids As String = GrabIDs()
Dim IDCount As Long = ids.Split(CChar(",")).Length - 1
Do Until IDCount = 0
[Code]....
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May 27, 2012
I'm getting a Cross-thread operation not valid error when my label text changes - this is very strange because it was working up until yesterday.The only way I can get this to work is by applying the invoke..[code]Is there a more simpler solution or will I have to invoke all my label coding?
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Mar 21, 2011
I use background worker almost daily and works great. Today I came to an instance though where I needed to put my background worker in a separate project then the one I was running because I needed to use this class in two different projects in my solution. When I tested the coding on a winforms form, it works perfectly, handling my coding on the background thread. When I try to reference this class from an external project, all of my coding seems to run just fine, but it does not appear to be doing anything on a background thread as it should be, causing my main window to lockup.
Is there any way around this / what is the best practice for ASYNC calls in an external class.Note I basically created a class that u call start, and an event fires when data is ready, so it's not like my external project is waiting for the method to complete.
Solution ABC has two projects. Project A and Project B. Project A is my WPF application and B is my DLL doing the work. Inside project A I have
Dim SmartCardData as new Solution.B()
SmartCardData.Start()
Project B has a sub
[code]....
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Jan 14, 2009
Is it possible to create a new instance of the webbrowser class inside of a worker thread?
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Dec 11, 2011
how to put this on a background worker without getting cross thread errors??? trying to upload a childform object values to an access db.I don't work in IT,Our company's LAN so slow that it takes around 3~5 seconds trying to update/insert values in access using the code below so putting it on a background worker i think makes the app immediately usable once save/upload's called unless otherwise somebody could suggest a faster way to speed things up.[code]
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May 28, 2012
I am using a background worker to update a progress bar while inserting data in a database.
Private Sub InsertintoDB_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles InsertintoDB.Click
BackgroundWorker1.RunWorkerAsync()
[Code]....
the error i m getting is exception has been thrown by the target of an invocation.
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Nov 14, 2011
I tried to update the button text on a form from a backgroundworker.do_work event, and it failed, with the usual cross-thread exception message.However, by pure chance, I also tried to update text in a system.windows.form.toolstripstatuslabel also from this backgroundworker.do_work event, and it DOES work. Question: why is this? Is it perhaps because theres some kind of implicit shared behaviour with system.windows.form.toolstripstatuslabel?
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Nov 18, 2009
I have a program that runs for some time and I would like to update the user on its progress. The rest of the GUI is updated using Delegates and Invokes and such (Java is Soooo much cleaner in this regard - everything is thread safe!!), but there is no invoke method for the progress bar. How can I use a delegate to update the progress bar when there is no invoke to invoke!!
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Jul 1, 2011
I am trying to update a ListView control from 10 background worker progress. It is working well if there is only 1000 list in ListView control. But when the list is big then the update is not working properly. The different value is not updating the appropriate list index. Here is my partial code of worker progress:
Private Sub worker1_ProgressChanged(ByVal sender As Object, ByVal e As System.ComponentModel.ProgressChangedEventArgs) Handles worker1.ProgressChanged
SyncLock updmxresult
[Code]....
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Apr 23, 2009
I have a windows application that need to process som quite time consuming jobs. In my first try i did all processing under
the form thread. The result was bad response and update of the form due to the heavy jobs.To get around the problem with bad response from the form i created a new class "processing" where i put all the data processing. Then i instanciated a background worker where i in the "doWork" sub created a new instance of "processing".The "processing" class creates a timer from system.timer, and the timer drives the processing.On the Timer event Elapsed the timer starts a new thread from the thread pool.
My problem is now when i want to asynchronously close the background worker (with the corresponding function call what ever it is called ...) there is still a timer thread out there that causes exceptions for me.
1. How can i close my background worker and at the same time have the timer to be stopped?
2. Is there a way to synchronize the timer event so that the timer executes from the background worker thread?
3. Is there a better approach for me to adapt?
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Mar 11, 2009
I have the following code that adds a background worker into a VB.net WPF project:
Imports System
Imports System.ComponentModel
Imports System.ComponentModel.BackgroundWorker
[Code].....
And I get the following error for the DoWork worker event:
Handles clause requires a WithEvents variable defined in the containing type or one of its base types.
It seems like it's missing something in the Event declaration, but can't find it.
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