Expiring Today—Celebrate National IT Professionals Day with 3 months of free Premium Membership. Use Code ITDAY17

x
?
Solved

backgroundWorker.. DoWork and ProgressChanged

Posted on 2006-12-01
10
Medium Priority
?
4,528 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
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 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
What is SQL Server and how does it work?

The purpose of this paper is to provide you background on SQL Server. It’s your self-study guide for learning fundamentals. It includes both the history of SQL and its technical basics. Concepts and definitions will form the solid foundation of your future DBA expertise.

 
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 2000 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

 [eBook] Windows Nano Server

Download this FREE eBook and learn all you need to get started with Windows Nano Server, including deployment options, remote management
and troubleshooting tips and tricks

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…
In my previous two articles we discussed Binary Serialization (http://www.experts-exchange.com/A_4362.html) and XML Serialization (http://www.experts-exchange.com/A_4425.html). In this article we will try to know more about SOAP (Simple Object Acces…
This tutorial will teach you the special effect of super speed similar to the fictional character Wally West aka "The Flash" After Shake : http://www.videocopilot.net/presets/after_shake/ All lightning effects with instructions : http://www.mediaf…
Have you created a query with information for a calendar? ... and then, abra-cadabra, the calendar is done?! I am going to show you how to make that happen. Visualize your data!  ... really see it To use the code to create a calendar from a q…

719 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