Multithreading - Load Data In Background Mode Using Background Worker?
May 3, 2012
I am using query from a SQLite database as the AutocompleteCustomSource for a ComboBox. Also, I want to load data in separate thread. My LoadData method works fine when called directly, but it fails when it is called from the BackgroundWorker thread. When it is called from the background thread, it throws a Specified cast is not valid exception on the csearch.AutoCompleteCustomSource.Add(hh("Taj")) line. Below is my code:
Sub LoadData()
Dim connetionString As String
Dim cnn As SQLiteConnection
I have a DataGridView that I'd like to load with data that I'm retrieving from a SQLDataReader running in a background worker as the data comes in (it's a query that takes a long time). My goal is for the user experience to be similar to searching for a file in Windows where the results appear in the list as they come in and you can still interact with the window.
I have it working with a background worker and data reader and I'm trying to add the row from the SQLDataReader.Read through using the BackgroundWorker.ReportProgress method. Everything technically works but the flicker is crazy and the form is unusable (probably not because the GUI thread is blocked but just because there's so much going on...) How do I make loading the datagridview "smooth"?
I have created a background worker using a tutorial. I understand some basic stuff like how to update a label or a progress bar from inside of it. The purpose of this background worker is setup a bunch of variables that are going to be used by several other background workers later. The variables i am setting up are 6 different lists and a multi-dimensional array. The code looks like this for the background worker at the moment.
Private Sub My_BgWorker_DoWork(ByVal sender As Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles My_BgWorker.DoWork For i As Integer = 0 To m_CountTo
[code]....
I would normally use the persons.add to add something to the list, but I'm having a really hard time wrapping my brain around an easy way inside of the backgroundworker to add new values to several different lists(which are going to vary in amount of data values). Is there an easy way to do this? I'm used to just having invokes at the top of a sub to do this but those don't seem to work inside of a dowork sub.
Im using Vb.net visual studio 2008. i have got a process(system.diagnostics.process) to be run in background and it updates the Ui thread progressbar and a label and i have worked it using backgroundworker.runworkerAsync. Now the problem is i have to work the same process for a number of time with different inputs.
The code block is :
Private Sub fnStartEvent(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnStart.click Dim inputFolder = Directory.GetFiles(textboxSourceFolder.text) Dim currentNumberOfFile As Integer=1
[code]....
The problem in here is the fnStartEvent method once gets started, it calls BackgroundWorker1.runWorkerAsync process and that runs in a seperate thread and does not wait for the thread to complete and it moves to the next line of code i.e loops to the next item and it returns to same BackgroundWorker1.runWorkerAsync line and throws exception that it is already running.
Tried
1. Private Sub fnStartEvent(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnStart.click Dim inputFolder = Directory.GetFiles(textboxSourceFolder.text) Dim currentNumberOfFile As Integer=1
[code]....
But this does not updates the Ui thread used to denote progress.
2.Put the whole process inside the DoWork thread and loop for each file in there itself, but that to returns the cross thread error in progress bar updation.what is the standard procedure in executing a loop for the backgroundworker to wait for finishing as well as update the UI without blocking it.
I have an application that queries DHCP and pulls scope/subnet information. There are roughly 8k scopes on our network to query so reporting this data takes a little bit of time. I currently have this running on it's own thread and reporting to a progress bar so the applications doesn't seem inactive.
The DHCP api functions can report a total, a max read and a resume argument. This means that I can, in theory start 4 threads and have each thread read through 2k subnets, so it will only take 1/4 of the time to read all this data. Would I need to create four separate background worker handlers, do_works, runworkcomplete, report progress etc.?
I'm writing an application in Visual Basic Express 2008, part of the function being to walk through a folder structure starting from a user specified folder. In my research, I found this thing called a background worker which seemed an appropriate tool to use given the potential size of a target folder structure. I successfully installed the two examples from the library here, and believe I understand the principles involved. Even so, having tried to build this feature into my application, it seems as though it is not working as expected, and, as predicted, debugging a multi-threaded application is a pain in the extremity.
I have this fragment under my "start" button click event -
my backgroundworker as I just cant get it to work. Basically I have a backgroundworker which does a few tasks but I'm trying to implement a progress bar and a label. I'm going to set the maximum value of the progress bar to 10 and then have it updating as I move with each task, also I'm thinking of a label with the progress bar which will display the progress ie
I have a background worker that used to fire its RunworkerCompleted event when its DoWork routine finished querying a database and writing its output to a file. The bg worker was in a class called Query, which was called from another class called Trigger. A new Trigger Class was created for each monitored event. In this class, there was a structure which stored the config of each Trigger. When this event was triggered (set to TRUE) a new query class is created and it is passed the Trigger class. When the database query, file writing was done, the query class and all its rsources were diposed from the RunWorkerCompleted EventRecently I changed the application so that a new trigger class is not created for each monitored event. There is a single instance of the class but new config structure for each event. When a particular event is trigger, jsut the config structure is passed to a new query class and the sma ething is done in the query class. I just noticed now that the RunWorkerCompleted event is not being fired anymore.
I have an issue that I can't seem to find a straight answer for anywhere... I have a For loop that sends a file name to a background worker that contains some long running code and I can't find a way for the parent thread to wait for the background worker to finish... Here is the example code:
For 4 BacgroundWorker1.RunWorkerAsync(fileName(i)) Next
I have run into this before, When I develop a form to use a background worker to fill tableadapters, the background worker does fine on machines running Vista, but if you run the same thread on an XP machine, the thread gets hung.All the thread is doing is filling a table adapter like this.[code]Why would this run on a Vista machine and not an XP machine?
I have created a background worker to go and run a pretty long task that includes creating more threads which will read from a file of urls and crawl each. I tried following it through debugging and found that the background process ends prematurely for no apparent reason.
While Not myreader.EndOfData Try currentRow = myreader.ReadFields() Dim currentField As String
[code]....
This first bit of code is the loop to input from file and this is what the background worker does. The next bit of code is where the background worker creates threads to work all the 'landingPages'. After about 10 threads are created the background worker exits this sub and skips the file input loop and exits the program.
Try For Each landingPage As String In landingPages pgbar.Timer1.Stop() If VisitedPages.Contains(landingPage) Then
[code]....
Also my main thread runs a forms from where this background is called to run but the main thread is supposed to wait for the background process to end unless the user selects another option from the main form.
I've been experimenting with background worker to maintain responsiveness and to allow the UI to update while things are being done in the background.I've been having problems getting the background worker to do anything with form controls.For simplicity lets say I have form1 and form2.The background worker is on form1Initially I couldnt get it to edit controls on form1 but by using [code]However the problem came when I tried to get the same background worker to update controls on form2, in this case a text box. With the above code there is no error but it also does not update the text box.Is there an easy way to give a background worker access to multiple forms.
Is there a way to pause a background worker? What I need to do is pause a background worker when it encounters a file error, wait for a few seconds, and then carry on.
I have a backgroundworker which does a few tasks but I'm trying to implement a progress bar and a label. I'm going to set the maximum value of the progress bar to 10 and then have it updating as I move with each task, also I'm thinking of a label with the progress bar which will display the progress ie [code]
How can i run it as a background worker? so it can run in the background where it does not effect my current running function - basicly so the form will not freeze at all.
I am developing a VB application along with MS Access... When I initially load my form I need to put my application to sleep for 3 seconds or else data wont load properly. So for this 3 seconds I would like to show a progress bar displaying a message "Please wait" I tried using background worker but did not find any success... I have gone through many tutorials but for some reason could not accomplish the task.
I'm new for VB.Net 2008. I am facing some problem about how to make the multiple groups activities running (it might concurrent) based on their own activity's time set? For example: If there is 80 groups and 100++ activities in each group, can i use background worker (create 80 background worker?) to handle this (each background worker handle their group activities.) if in this case (But it will running lag or hang)
I want to use a background worker control in my application, and have it report progress to a Progress Bar It will download data and stuff, and I want to be able to change the text on a label.
My application will creates an Excel from DB, creating an excel file takes few minutes of time and till that time the user dont want to wait for the excel to complete, he should start working with the application. Once the excel have been completed the appilcation should po-up message saying, 'Report Sucess'. can any one tell me how to do this, whtr background thread will help me in this ?
I am trying to code a simple background workers class without needing to use the backgroundworker object on a form. This would allow me to use a background worker in any class without writing much additional code. Is it possible to pass in the name of a sub at runtime instead of hard-coding it? To do this I would replace onDoWork and onProgressChanged below and use (Byval onWorkSub as SomeKindOfObject?, Byval onProgressChangedSub as SomeKindOfObject?) instead. [code]
I just can't see what I am doing wrong here, since I have implemented a progress bar into my background worker it no longer only runs the once (in some cases I have seen the coding within the foor loop run 6 times)
My coding:- My progress bar max value is set to 10. BGWorker Do Work Event
ive developed my app and am im trying to improve its use ability. Ive created a dvd management app for myself and i have a function that retrieves all the data for all the movies displayed in my listview. It works fine but the interface hangs for the entire time.Ive decided to use a background worker so i can browse other movies with all the data is being fetched.Im having silly problems with getting the index value for my listview when im using the .DoWork()
ive had these errors:
1. Cross-thread operation not valid: Control 'ListView1' accessed from a thread other than the thread it was created on.
2. nvalidArgument=Value of '1' is not valid for 'index'. Parameter name: index
the function works a dream whenvnot being called inside the doWork()
'New Objects Dim fetch As New Create Dim download As New Download Dim parse As New Parse
I have created a background worker to go and run a pretty long task that includes creating more threads which will read from a file of urls and crawl each. I tried following it through debugging and found that the background process ends prematurely for no apparent reason. Is there something wrong in the logic of my code that is causing this. [code]Also my main thread runs a forms from where this background is called to run but the main thread is supposed to wait for the background process to end unless the user selects another option from the main form.
I just started fooling around with background workers.
Up in FORM_LOAD somewhere consoleBW.WorkerReportsProgress = True consoleBW.RunWorkerAsync()
[Code]...
I can see how this runs regardless of what I'm doing in the main form - modal dialog boxes - whatever.
Now what I really want to do is have this background worker check to see if the DB has changed since we last created some classes that hold the data. I basically want to set a property in the CLASS that indicates the need to get fresh data.I discovered all the problems with cross-threading calls to UI objects - so I used the PROGRESSCHANGED event. just set a property in a data class created by the UI from the background worker?
