I have a backgroundworker that is downloading data from different webpages and process them to a datagridview.I get the Cross-thread operation not valid error on the first For loop.
Private Sub BackgroundWorker1_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
dim i as integer
tot = (numPostnrTo.Value - numPostnrFrom.Value) / 10
[code]....
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".
I have a VB.NET 2010 app that uses a backgroundworker to process MS Word docs. All of the code does what it is supposed to do, except when my code calls ReportProgress(). The UI cannot process the ProgressChanged event fast enough before the values in the class that are passed are changed. I know this because I inserted a System.Threading.Thread.Sleep(100) line after each ReportProgress() call which allows time for the UI to make the updates properly. I guess I am looking for a better solution thanThread.Sleep(100) since this adds to the amount of time it takes to process all of the files. Here are some snippets of code that I am using:
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A BackgroundWorker thread can pass data to the primary thread. It does it via the RunWorkerCompleted and ProgressChanged events, which I believe run in the primary thread. I would like to encapsulate the BackgroundWorker control in a class so that I can instantiate it more than once. But I don't know how the BGW can then communicate with the primary thread. If the BGW control is within a class, it does not have access to the properties outside the class. In that case, how can the BGW pass data to the thread that instantiated it?
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I'm working with BackgroundWorker, I want the BackgroundWorker do the retrieval process of data from database while the user can still do another task on the form. The problem is, after retrieving the data, I can't seem to access the ListView in my Form from the DoWork event of BackgroundWorker, I will populate that ListView using the data I've retrieved.
Consider this example, this is how I'm doing it:
Public Class Test
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
[Code].....
How do run processes synchronously from a thread or backgroundworker thread? Is it even possible?We have program that allows the user to download several files from a remote server, compress them, and then email the files.It has several long running processes that must run in order. We want these to run on a separate thread so as not to make the form unresponsive. Does a way exist to do this? We attempted a rather clumsy way of approaching this problem by using background worker threads. When each thread is completed and returned back to RunWorkerCompleted, we start another background worker thread and repeat the the next process. It works somewhat but seems to take a lot of resources to run.
View 1 Repliesi got error when
1.) Looping exceed the images files found in the folder
2.) When program get not valid file
3.) when changing the source of images
the error says "Parameter is not valid"
here is the code below....
Function getnewImage()
Try
If (Me.Ping.Send("pc1", 6000).Status) = Net.NetworkInformation.IPStatus.Success Then
[Code].....
For my own basic understanding ... what is the difference between these two snippets?
Dim y As Integer
For x As Integer = 1 To 100
y = x
[code].....
Today I investigated a logical bug in our software and figured out that this is related to the way VB.NET thread variables inside a loop.Let's say I have the following code:
Dim numbers As New List(Of Integer) From {1, 2, 3, 4, 5}
For Each number As Integer In numbers
Dim isEven As Boolean
[code]....
The problem is that isEven is declared but not assigned.In this specific case, it would be correct to write dim isEven as Boolean = false but I haven't done this.In VB.NET, a variable that is declared inside a for loop keeps its value for the next itaration. This is by design: [URL]but this is also dangerous pitfall for programmers.
However, until now, I haven't been aware of this problem/behaviour. Until now.Most of our code base is C# anyway, which doesn't allow the use of an uninitialized variable, so there is no problem. But we have some legacy code that is written in VB.NET that we have to support. So the best thing would be to generate a warning or even an error in this specific case.But even with Option Explicit / Option Strict this does not generate a warning / an error.Is there a way make this a compile time error or maybe a way to check this with FxCop?
I cannot figure this one out.. I have a background worker that will perform a task streaming data from some webpages. this data is then passed back and displayed in a gridview. It has been working fine.
I've recently implemented a listbox, which its values will be passed into the function that the background worker will perform as parameters, originally i had taken a single value from a textbox.
Now, I thought maybe it had something to do with the listbox, so I used a static value, just a simple String, as the parameter, and again, I get the TargetInvocationException was unhandled.. There's no difference in how I perform the task I'm trying to have the backgroundworker complete, the only difference is where it exists in my if condition statement:
Private Sub BackgroundWorker1_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles ScrapeSites.DoWork
Dim results As ArrayList
Dim worker As System.ComponentModel.BackgroundWorker = DirectCast(sender, System.ComponentModel.BackgroundWorker)
[Code]...
in my button click event i ececure
If BackgroundWorker4.IsBusy Then
BackgroundWorker1.CancelAsync()
End If[code]....
after proceess completed if press the button again.i got the following error msg
This BackgroundWorker is currently busy and cannot run multiple tasks concurrently.
i'm in the need to start a backgroundworker inside another one.Now...The first one BGW starts a for cycle, and inside this one there is the second BGW that has to upload an image to a server.The trouble is that, the progress event and the complete event of the internal BGW are never called.
View 11 RepliesI 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.)
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
I have this little application that runs a SQL query works great, now I want to have a Start Button run the and display results then System.Threading.Thread.Sleep(300 * 1000) for 5 min then run again and display results and loop till I buttonstop_click. unsure if the sleep is the best method.
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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]....
im sorry if this has been asked before.but i couldent find it in my first look i have a form that runs a query on a mysql database but as it runs the query the form stops responding till it finishes sooo i had the smart idea of putting it in a back ground worker..
GREAT i thot i had it working it all seemed to go greeat then i noticed when i try to change the label text on the form to corispond to the info it got... it wont work it give me a cross threading error....
how to cross thread between the back ground worker and the origial form..
I wanna sleep a second thread of BackgroundWorker. I tried to use Me.Dispatcher.Thread.Sleep(500) in DoWork event, but it fails.
View 3 RepliesI have some classes right now that I have that I reuse for Client/Server programming. I'm using Thread in these classes though for monitoring for things being written to the network streams and stuff like that. I'm just not sure if I should be using the background worker class instead. I'm also using TCPClient and Listener classes, should I be using sockets directly? I guess it would all depend on the flexibility I would need in a given application's specs.
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I am writing an 'Admin Console' that accesses hMailServer via its provided COM interface. I am using Visual Basic 2010 Express. In one procedure, it scans for the whole accounts. Because it's a lengthy procedure, I shove it into a set of BackgroundWorker threads.
First result: A maximum of 19 simultaneous threads, with 36 seconds total time.Then I rewrote a time consuming thread initialization code segment, and managed to reduce the time required to approximately 14 seconds... but the thread count now hit 330 threads!Will that huge amount of threads be detrimental? E.g., causing out-of-memory exceptions &c. ?
I am using the BackgroundWorker to do the heavy tasks so the UI thread doesn't get blocked. While the BackgroundWorker can send values to the UI thread using the progress-scheme, how can the BackgroundWorker get some values FROM the UI thread?
Either by asking it or simply by the UI thread sending some values to the BackgroundWorker?
Just accessing a variable of the UI thread like UIForm.x within the BackgroundWorker does not work, it does not seem to have access to the UI variables?
I have a background worker that's checking the status of four services on a remote server.This is setup on a timer (5 Seconds) as below. For some reason it's hanging the UI thread causing the application to 'lock' for a second each tick, I cannot work out why?!
Private Sub ServiceTimer_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ServiceTimer.Tick
_ServiceBGWorker = New System.ComponentModel.BackgroundWorker()
[code]......
Well to simplify it, whenever I use sendkeys from a background thread it just doesn't work. I even created a textbox, button, and backgroundworker with the following code:
Public Class Form1
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
[Code].....
I'm running some tasks on a BackgroundWorker thread and needed to display the current tasks in a label.Before adding the label, the tasks were completing just fine and the UI was responsive.Once I added the labels, the UI has become unresponsive. The issue, I believe, is the Invoke property.I've declared all my tasks, including the updating, in a sub and am getting the Invoke property of the label each time, in order to set the information.The following is an example of what I'm doing:
VB.NET
Private Sub Test()If lblTask.InvokeRequired = True Then Dim mi As New MethodInvoker(AddressOf Test) lblTask.Invoke(mi)
[code]....
I have a situation where I'm using BackgroundWorker to run a long process in the background. However, whenever it runs I keep getting the following error:
"TargetInvocationException was unhandled"
The culprit seems to be this guy: Dim GrainProcess As New Process()
In my DoWork sub I'm calling a sub in another module. The above line is in the middle of that other sub. I'm using Process.Start to run a Matlab executable file (not written by me) that processes an image and spits out a number.
I tried putting the Dim statement outside the sub, but then it just gives me the same error a couple of lines down when I try to set the .StartInfo properties.
Does the "was unhandled" part of the above exception mean that I need to provide some kind of error checking (maybe a try...catch), or does it mean that I'm not allowed to do a Process.Start from within a BackgroundWorker thread?
I have created what amounts to a progressbar which is launched using a backgroundworker. So all is well the main UI/process is doing its thing and the progressbar is ticking away. What I would like to do is update some text that is in the progressbar. So when the main UI/process finishes one of its tasks I want to update a message in the progressbar. NOT have the progressbar update the main UI/process but rather have the main UI update the progressbar.
View 7 RepliesYes, I see what you mean. But I had to do it that because I tried to do it this way:
CODE:
but its says "Cross-thread operation not valid: Control 'RichTextBox1' accessed from a thread other than the thread it was created on."
What is the difference between creating a thead using BackgroundWorker and creating a thread using System.Threading.Thread?
View 2 Repliesi have lurked on these forums before and finally signed up..i have a situation that, after days of searching the web, i have not been able to come up with a solution for.i have to fire off a function that takes a large amount of time (writes to database, creates files, etc etc)this function is a non-shared function of a class. if need be i could make it Shared.[code]the code works great, but what i need to be able to do is update a form with a progress bar as the job is processing.all of the examples i have seen that do this are being called from within a Windows Form and they access the form directly - i cant do that in this case. my form needs to be 1 form for 1 job being executed - can process multiple jobs at one time and thus i need multiple forms.i have tried making the form part of my delegate class but since it runs in the same thread the effect is it "freezes" until the job is complete.i have just started looking into using a background worker but again, all examples i have seen use the component as part of a form - that wont work for me.
View 3 RepliesI'm trying to add information to a ListView from a BackgroundWorker thread. I thought I could do this in this manner:
vb.net
Private Delegate Sub _ListView(ByVal lvi As ListViewItem)
Public Sub test(ByVal lvi As ListViewItem)
[Code].....
When I attempt to run the "test" sub the BackgroundWorker, I get an error:
Argument not specified for parameter 'lvi' of 'Public Syb test(lvi as System.Windows.Forms.ListViewItem)'.
Is there something I need to specify when declaring the sub, or in the sub itself?