I've seen a good bit written on avoiding updating a form from a thread.However,I was wondering if that was a problem if the thread exists in an object that programatically builds the form?Thus the form and associated logic exist within the same "thread space." Seems on the face of it like it would work since everything in the form should be in a single dispatch queue.
View 8 RepliesI have an MS Access database and an MS Visual Basic 2008 front end.I get this error when trying to update a record that has related records:The record cannot be deleted or changed because table 'X' includes related records.I only want to update one field in the row in the 'parent' table which is not the primary key field of either record but the 'Update' command seems to want to rewrite the whole datarow. Rewriting the whole row causes the error (as this updates the primary key). If I switch off refrential integrity checking in the underlying database this solves the problem except that I want to maintain referential integrity so its not really a solution. I have tried beginEdit and EndEdit with no success - same error.Is there a way to update just one field in a row and write that back to the database?
View 2 RepliesI have a VB.NET 2010 app I am writing that does a lot of work on a RS485 bus in 2 seperate threads. These threads are started as soon as the app is opened and run as long the app is open. I would like to have the threads update labels on the main (and only) form every so often based on what's happening on the serial bus. I know it involves invokes and delegates but I haven't found a straight forward answer on how to implement it.
View 5 RepliesI'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?
Here is a sample of the VB6 code:
Code:
Dim StartTimer As Double
StartTimer = Timer
Do
[code]....
I am trying to implement a solution for updating form controls without using a delegate.
Imports System.ComponentModel
Imports System.Runtime.CompilerServices
Public Module MyInvoke
[code]....
I get a cross threading error as though i didnt even use this method:Cross-thread operation not valid: Control 'ComboBox1' accessed from a thread other than the thread it was created on.
I'm having some problems with updating a form from a background thread, started in the MyApplication_Startup sub.As far as I know updating forms or controls on forms have to be done threadsafely.
When the application starts up, some threads are being created which create an object in which a download for a zipfile will be started. The object has some delegates to let the GUI know what the status of the download is, for example 'started' or 'finished'. Also the mainform will be shown on which a datagrid has been placed to show the user which files will be downloaded and in which phase the download is.
All this works amazingly fine but when I want to update the datagrid's cells p�r thread the datagrid aint updated. I know the problem is that the thread in which the Form is created isn't the same as the thread which wants to update the grid?
I have a small problem that I am sure is due mostly to my inexperience with threading. I have used simple entirely self-contained threads before, but not to a great extent. I understand the basic laws that surround them, such as how a thread cannot access another thread's member directly, and must use delegates.
[Code]...
loading of form when I experiment with Debug.Write code?I deleted the form,placed code in a standard module before running the program but am getting an error message.With the form existing I get what I want but I just don't need to wait for the form to load and then to click cancel to close it.Is it not possible to have just a standard module in a VB 2010 Express project? If not can't I place the code in form1.vb but stop it from loading every time I test something?
View 10 RepliesWe have an issue with an application where we are making a call to an asynchronous process on LostFocus of a TextBox, the asyncronous process then needs to be able to update the main form UI (or display a dialog from the main form UI) while running asynchronously.We have thought about call backs and having it truely asynchronous but we need everything to execute in the correct order and this is for a data entry system where speed and accuracy of data entry is important.Example code shows what we are trying to do and if you switch to Begin Invoke the order of processing is not correct.[code]Does anyone know how we can invoke something else on the main form thread while is is still busy processing the LostFocus event?
View 2 RepliesThe program i am writing has 5 features, all of which i want to run in their own threads. On the main for I have a listView which contains all the accounts (user password etc). The thread is defined as:
Public fbaThread As New Thread(New ThreadStart(AddressOf fba_Start))
In cmdAdderStart i begin the new thread by:
fbaRun = True
fbaThread.Start()
[Code]....
I have managed to write the UpdateDebug() to update my txtDebug on the main form. But now I am having trouble being able to pull the values from lvAccounts.items().subitems I can accomplish this with global variables but i'm sure this is not the best way to do this.
I am writing a basic application to provide remote support to multiple computers over a TCP Stream. For example, if my brother/dad has an issue with their computer, rather than going over to help them I can just use remote support (Yes, I know Windows has Remove Desktop, and their is TeamViewer, ect. But where is the fun in using those =P)Anyway, it basically works by taking a PrintScreen of their computer, sending it to mine and displaying it in a PictureBox, then when I click the image, it records the coordinates of my mouse, sends it to theirs (Little Maths for resolutions and positions ofc) and clicks, then sends a new image.
My problem is, I want a ListView displaying the PC Info, like:
PCName - RAM - Free HDD Space - 32/64Bit - Processor Speed
Now, my problem is, I have a Class which does the TCP Server, and in that class when it Receives a Message, it calls the Sub "RunCommand(ByVal Command As String)", which then splits the String and works with it.So, for example, their PC would send the String "Info|DadPC|2GB|235GB|32Bit|2.2GhZ|" And mine would split it, and add that data accordingly.However, what happens is, nothing. If I put in "MsgBox()" anywhere in the Code, it shows it is all Split, and received correctly and everything is fine, but no matter what happens, it wont add to the ListView (Or anywhere else on the form, for example "GUI.Text = Info(1)" Wont work either)?
I have been trying to update a textbox on the main form of my program using a different thread, however the changes are not relected in the textbox.I am using MS Dev studio 2010 beta 2.0 .NET 4.0. Here's my code....
The main form
Code:
Public Class frmMain
Private Engine As New clsEngine
Private txtMessage As String
[Code]...
I've got a bunch of labels that I update regularly in the program, resulting in lagg, which is bad, so how can I update the labels in a thread?
When I try
Thread = New System.Threading.Thread(AddressOf ShowInfo)
Thread.Start()
[Code]......
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] .....
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 few classes. One of the classes handles everything to do with updating controls (Such as adding items to a listview, etc.) and another is handling loops. I'm trying to add something to a richtextbox from another thread.[code]..
View 3 RepliesI have got this module which copies a specific folder and all files inside it.[code]...
View 8 RepliesI have some controls in a .net 4.0 form - a listbox and a listview item.I also have another thread in the same class which is checking a host for output.It uses delegates to display all incoming data to a richtextbox - this works fine.If the data has a particular signature it sends it to a parser sub in another module.This module tries to update the listbox and listview items with that data after it has manipulated it.The problem is; no data is displayed and no errors are thrown.If I add a msgbox("Test") after the code, it shows the messagebox.If I add a test messagebox inside the delegate function, it shows the messagebox. If I put the same MainForm.ListBox1.Items.Add("Howdy") in a ButtonTest.Click event it adds it correctly.
View 14 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've been programming in vb.NET for a whileAnd to be honest, its turning out to be a real pain.Here is the
Form1.vb: Imports System.Threading
Public Class Form1
Dim trd As Thread[code].....
So, I have a form (form1) with a label on, this label simply reports the status of the thread.The thread begins the Class1.Main() sub, and I have a delegate setup to change the text propoerty of the label.Now,I know the label is created on the UI thread,so I assumed the delegate would work. However,it seems that it updates the .text property, but doesnt redraw the control when .Update() is called .What am I doing wrong?I have found lots of examples of delegates, but all run from within the same class. I want to use threads too, not a backgroundworker! This code is a "simplified" version of a project I am on, which is encountering the same problems
I'm using the following to check the state of checkboxes and then activate some public subs based on the checked state of the checkboxes:
vb.net
Public Sub TestSub() If Me.CheckBox1.InvokeRequired Then Me. CheckBox1.Invoke(New MethodInvoker(AddressOf TestSub)) Else Begin() End If End Sub
Within the Begin sub, I have code that performs specific actions and then updates a ListView with that information.As far as I can tell, the actions are being performed, but the ListView isn't being updated with the info.I'm calling the Test sub from a seperate form, within the BackGroundWorker's DoWork event.Would I have to check the InvokeRequired property of the ListView as well?I'm looking more into the documentation of the BackGroundWorker.
I have a windows form with a progress bar and a button to start/stop the process. I am performing some action when clicked on 'Start' and updating the ProgressBar accordingly and its working fine. But when I try to click on the 'Stop' button when the process is going on, I couldn't access the Window. If I click for multiple times, I am getting (Not Responding) on the titlebar.
Then, I created a thread and run the function (which performs my task and update the ProgressBar) in it. I am getting an error that it could not access the control which is created in another thread.
Private Sub runExe()
Dim myProcess As New Process()
Dim myProcessStartInfo As New ProcessStartInfo("mkclean", " --optimize """ & txtSrcFile.Text & """ """ & txtSaveFile.Text & """")
[Code]....
I have a very long running process that I start in a thread. This raises events with messages to say what it is doing. How can I update a label on screen with these messages? (The label is in an update panel if that makes it easier).
View 3 RepliesI'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]....
I am currently working on a project that has a splashscreen This splash screen is designed to be shown when the main form begins to load its requirements, and then closes once it has loaded... Currently it works like so:
Private Sub frmMain_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
frmSplash.Show()
dolotsofloading()
frmSplash.Close()
End Sub
[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'm working on a website where we'll be getting a lot of videos to be uploaded. To keep things simple and secure, I'm just writing VB.net windows app to suck all the files in a directory in, allow you to set some options, and start the encode by spawning a new FFMpeg process.
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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.
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.)