Solved

backgroundWorker.. DoWork and ProgressChanged

Posted on 2006-12-01
10
4,518 Views
Last Modified: 2008-01-09
Hello,

I using a backgroundWorker to execute a time consuming operation and print the result as they come an a listView. I'm basically doing something similar to the following:

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
            while (condition)
            {
                if (backgroundWorker1.CancellationPending)
                {
                    e.Cancel = true;
                }
                else
                {
                    // code... bla bla bla
                   
                    globalItemName = someVar;

                    Console.WriteLine("In DoWork");
                   
                    backgroundWorker1.ReportProgress(1);
                }
            }
}

        private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
        {
            Console.WriteLine("In ProgressChanged");

            listView1.Items.Add(globalItemName);

            progressBar1.Value = e.ProgressPercentage;
        }

It's not working, all the 'In DoWork' is printed in the output window first then 'In ProgressChanged' is printed after.

What's wrong?

Thanks.
0
Comment
Question by:i950
  • 6
  • 4
10 Comments
 
LVL 48

Expert Comment

by:AlexFM
ID: 18058891
>> 'In DoWork' is printed in the output window first then 'In ProgressChanged' is printed after.

This is exactly what is written in your code:

Console.WriteLine("In DoWork");
backgroundWorker1.ReportProgress(1);          // In ProgressChanged

What is the problem exactly?
0
 

Author Comment

by:i950
ID: 18059629
Hi Alex,

I'm getting:

Console.WriteLine("In DoWork");
Console.WriteLine("In DoWork");
Console.WriteLine("In DoWork");
Console.WriteLine("In DoWork");
Console.WriteLine("In DoWork");
Console.WriteLine("In DoWork");
Console.WriteLine("In DoWork");
Console.WriteLine("In ProgressChanged");
Console.WriteLine("In ProgressChanged");
Console.WriteLine("In ProgressChanged");
Console.WriteLine("In ProgressChanged");
Console.WriteLine("In ProgressChanged");
Console.WriteLine("In ProgressChanged");
Console.WriteLine("In ProgressChanged");
Console.WriteLine("In ProgressChanged");

Not:

Console.WriteLine("In DoWork");
Console.WriteLine("In ProgressChanged");
Console.WriteLine("In DoWork");
Console.WriteLine("In ProgressChanged");
Console.WriteLine("In DoWork");
Console.WriteLine("In ProgressChanged");
Console.WriteLine("In DoWork");
Console.WriteLine("In ProgressChanged");
0
 
LVL 48

Expert Comment

by:AlexFM
ID: 18059720
I made small test and reproduced this behavour. This means, BackgroundWorker.ReportProgress invokes ProgressChanged event asynchronously. Line
backgroundWorker1.ReportProgress(1);
is executed, and worker thread code continues immediately, without waiting for ProgressChanged function. Computer makes thread switch with some time interval. In your case, backgroundWorker1_DoWork function is executed in one time interval scheduled to this thread. When thread exits, main thread is activated and executes all ProgressChanged events from event queue.
Make small change:
backgroundWorker1.ReportProgress(1);
System.Threading.Thread.Sleep(0);

Now you can see expected result. Sleep(0) causes thread context switch, and ProgressChanged is called immediately.
However, Sleep(0) is added only for test, remove it. Asynchronous behavior of BackgroundWorker is absolutely OK, this is the way multithreading must work.
0
Master Your Team's Linux and Cloud Stack!

The average business loses $13.5M per year to ineffective training (per 1,000 employees). Keep ahead of the competition and combine in-person quality with online cost and flexibility by training with Linux Academy.

 
LVL 48

Expert Comment

by:AlexFM
ID: 18059739
BTW, you can add more code to backgroundWorker1_DoWork to make it more time consuming. This this case output will look like this (without Sleep):

Console.WriteLine("In DoWork");
Console.WriteLine("In DoWork");
Console.WriteLine("In ProgressChanged");
Console.WriteLine("In ProgressChanged");
Console.WriteLine("In DoWork");
Console.WriteLine("In DoWork");
Console.WriteLine("In ProgressChanged");
Console.WriteLine("In DoWork");
Console.WriteLine("In DoWork");
Console.WriteLine("In DoWork");
Console.WriteLine("In ProgressChanged");
Console.WriteLine("In ProgressChanged");
Console.WriteLine("In ProgressChanged");
Console.WriteLine("In ProgressChanged");

Every thread executes its work in time interval given to this thread by operating system. This is exactly what we expect from parellel asynchronous execution.
0
 

Author Comment

by:i950
ID: 18059758
Ahaaaa... it's clear now.

So my whole idea to update the UI in ProgressChanged not going to work as expected. What I'm doing is declaring a global variable for the listView item text and I assigning this variable in DoWork then I call ReportProgress and in ReportProgress I use the global variable to get the list view item name, which may or may not be changed!!!!!

What's the correct way to update the UI in this case?
0
 
LVL 48

Expert Comment

by:AlexFM
ID: 18059780
Correct way is using BackgroundWorker.ReportProgress Method (Int32, Object) overload. It allows to add instance of any class or primitive type (like string) as parameter.

backgroundWorker1.ReportProgress(1, someVar);


        private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
        {
               string s = (string)e.UserState;
               ...
        }
0
 

Author Comment

by:i950
ID: 18059806
It worked! Thanks!

Just one more thing...

How can I pass several variables (integers and strings) to ReportProgress?
0
 
LVL 48

Expert Comment

by:AlexFM
ID: 18059870
You need to define your own class which contains all these variables, and pass instance of this class as parameter.

BackgroundWorkerData d = new BackgroundWorkerData();   // your class
d.name = somevar;
d.number1 = ...;      // fill with any data

backgroundWorker1.ReportProgress(1, d);

        private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
        {
               BackgroundWorkerData d = (BackgroundWorkerData)e.UserState;
               // read data here
               ...
        }
0
 

Author Comment

by:i950
ID: 18060075
Is there any performance overhead when initiating many BackgroundWorkerData here:

BackgroundWorkerData d = new BackgroundWorkerData();   // your class
d.name = somevar;
d.number1 = ...;      // fill with any data

I'll be using it in a loop that may be repeated several thousand times.
0
 
LVL 48

Accepted Solution

by:
AlexFM earned 500 total points
ID: 18060475
You must create new instance for every call. Maybe this is bit slower than using the same instance, but one instance doesn't work properly, as you see. Don't care about creating many instances, .NET Garbage Collector is very effective.
0

Featured Post

DevOps Toolchain Recommendations

Read this Gartner Research Note and discover how your IT organization can automate and optimize DevOps processes using a toolchain architecture.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Summary Displaying images in RichTextBox is a common requirement with limited solutions available. Pasting through clipboard or embedding into RTF content only support static images.  This article describes how to insert Windows control objects int…
Many of us here at EE write code. Many of us write exceptional code; just as many of us write exception-prone code. As we all should know, exceptions are a mechanism for handling errors which are typically out of our control. From database errors, t…
This video shows how to quickly and easily add an email signature for all users on Exchange 2016. The resulting signature is applied on a server level by Exchange Online. The email signature template has been downloaded from: www.mail-signatures…
Finds all prime numbers in a range requested and places them in a public primes() array. I've demostrated a template size of 30 (2 * 3 * 5) but larger templates can be built such 210  (2 * 3 * 5 * 7) or 2310  (2 * 3 * 5 * 7 * 11). The larger templa…

776 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question