Question

I have a Thread processing a binary file and storing it in a datatable.
While processing i am updating the progress bar with the current stream position.
My problem is; in the Thread I have a finally{} block, and in that I set the progressbar value to the max allowed value, then i run Application.DoEvents(); then I display a MessageBox, but my MessageBox always appears before the Progressbar fills.

here is the applicable code

here is a video showing the issue

I have created a small application to demo the use of a BackgroundWorker instead of a Thread. Here is the code

I am seeing the same ‘error’ ( I am Hesitant to call this an error, more a Usability issue ) As you can see I have also added a dirty little logger there. The output at the end of the log file is:

27/10/2011 4:58:29 PM – Progress Entered

27/10/2011 4:58:29 PM – Progress Changed to 79661

27/10/2011 4:58:29 PM – Progress Entered

27/10/2011 4:58:29 PM – Progress Changed to 79661

27/10/2011 4:58:29 PM – Complete Entered

27/10/2011 4:58:29 PM – Events Done

27/10/2011 4:58:30 PM – Message Shown

So there is not a problem with the order in which the commands are being executed… is my only real solution to add a delay before displaying the messagebox?

Answer 1

I would try replacing the Application.DoEvents(); with a simple Thread.Sleep(100). The documentation around DoEvents does not seem to indicate whether you are allowed to call it from another, non-UI thread. By using Thread.Sleep instead, you’re delaying the message box popup and allow the UI thread to process normally.

An alternative method to having the worker background pop up a message box is to use an event, and invoke the subscribed delegates on the UI thread (just like you do for the progress bar).

In fact, if you wanted, you could probably rewrite your thread code to use the BackgroundWorker object, and subscribe to the ProgressChanged and RunWorkerCompleted events. Your actual thread code would be responsible for calling the ReportProgress method to fire the ProgressChanged event to update your progress bar.

Response to update

After looking at your new code, you’re never setting the progress bar to the maximum value when your worker completes. In worker_RunWorkerCompleted add progressBar1.Value = progressBar1.Maximum; before you show the message box. That should update the progress bar to maximum before the message box pops up.