Updating Form from thread, whilst Form on Main thread is busy

Question

2.50/5 (2 votes)

See more:

Hi all

Wanted to know if anyone had sorted this at all:

I want to do something on a backround worker thread that updates the Form whilst the Form is busy doing something. When I say busy, it might be performing some queries on a database that could take a while.

As queries on the database essentially make the program hang, the background worker thread doesn't update the screen whilst the query is going on and I can't issue the queries on their own thread, as we're using an alpha DB, and the connection isn't thread safe.

Have tried a simple program with a background worker thread that is kicked off on clicking a button. Updates to the screen happen in the thread. Immediately after the thread is kicked off (.RunWorkerAsync) I simulate something happening like a query being issued by using a sleep for 10 seconds (Sleep(10000)).

The screen is not updated whilst the sleep is active, even if I use Application.DoEvents(). It does update without a sleep

I'm pretty sure what I'm askng is not possible, but you never know.

Thanks for reading!

Julian

Posted 27-Jun-11 2:35am

julian@giant

Add a Solution

3 solutions

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

#realJSOP · Answer 1 · 2011-06-27T02:42:00

Solution 1

First, there's no reason a form should be "busy". Your query should be in its own thread, and should notify the form when it's done via an event. At that point, your form is free to handle other events from other threads, such as a BackgroundWorker. Finally, why on earth do you have a Sleep method on the form's thread?

Posted 27-Jun-11 2:42am

#realJSOP

Updated 27-Jun-11 2:43am

v2

Comments

julian@giant 27-Jun-11 8:45am

That would be nice if the query was issued in a thread. However, the query is issued on the main thread and code execution stops until the query is finished. And as stated, I can't issue the query on it's own thread.

Am I missing something?

Kim Togo 27-Jun-11 8:51am

Why can you not run the query on a worker thread?

#realJSOP 27-Jun-11 14:45pm

Unless it's a code restriction, you *can* run this from a thread. just create the SQLConnection object as a public member in astatic class, and instantiate it. OInce that's done, a separate/background thread can access it, and when it's done, the connection remains open (uness, of course, the thread closes it). Just because the connection isn't thread-safe doewsn't mean your code can't be. It just requires a bit more caution on your part, that's all.

julian@giant 27-Jun-11 8:55am

The connection to the database remains open for the life of the application. The connection is created on program startup on the main thread. Issuing a query on a separate thread hasn't worked properly in the past, I don't think the interface to the DB is up to it. It's an alpha database running on VMS. We connect to it at the moment from a .Net application using ADODB.

julian@giant 27-Jun-11 9:18am

I don't think what I'm trying to do is possible. Thanks for your comments anyway.
Julian

Sergey Alexandrovich Kryukov · Answer 2 · 2011-06-27T17:41:00

There is another way for a non-UI thread to communicate to UI, much more general one.

You cannot call anything related to UI from non-UI thread. Instead, you need to use the method Invoke or BeginInvoke of System.Windows.Threading.Dispatcher (for both Forms or WPF) or System.Windows.Forms.Control (Forms only).

You will find detailed explanation of how it works and code samples in my past answers:
Control.Invoke() vs. Control.BeginInvoke()[^],
Problem with Treeview Scanner And MD5[^].

See also more references on threading:
How to get a keydown event to operate on a different thread in vb.net[^],
Control events not firing after enable disable + multithreading[^].

—SA

Kschuler · Answer 3 · 2011-06-27T07:53:00

The only way a background worker can communicate back to the form, as far as I know, is through the ReportProgress method which triggers the ProgressChanged event. But depending upon what kind of updates you are trying to make on the screen...this might be enough. For example, if all you are trying to do is change a label so it will report to the user that the process is now on Step 2, you can just setup the ProgressChanged event to do it. Here's a sample of how I've used values 0-9 when reporting progress to update labels and the progressbar on my form...and then any value greater than 9 sets the progressbar value.

VB

Private Sub bgwSync_ProgressChanged(ByVal sender As Object, ByVal e As System.ComponentModel.ProgressChangedEventArgs) Handles bgwSync.ProgressChanged
    Select Case e.ProgressPercentage
        Case 0
            'Error
            barProgress.Value = 0
        Case 1
            lblMessage.Text = "Checking for program updates..."
            barProgress.Value = 5
        Case 2
            'performing program update
            lblMessage.Text = "Updating program..."
            barProgress.Value = 15
        Case 3
            lblMessage.Text = "Processing Step One..."
        Case 4
            lblMessage.Text = "Processing Step Two..."
        Case 5
            lblMessage.Text = "Retrieving data..."
        Case 6
            lblMessage.Text = "Downloading files..."
            barProgress.Value = 15
        Case 7
            lblMessage.Text = "Loading tables..."
        Case 8
            lblMessage.Text = "Processing Step Three..."
        Case 9
            lblMessage.Text = "Processing Step Four..."
        Case Is >= 10
            barProgress.Value = e.ProgressPercentage
    End Select
End Sub

If you are trying to be more specific and want to report a string value like a filename or something and where it is being used in the process...you still might be able to use the idea above but you would have to get the filename or whatever the same way on the form as you do in the backgroundworker and use an integer value from 0 to 100 to reference it on both sides. So it's limiting, but might be possible.

Hope this helps.

Updating Form from thread, whilst Form on Main thread is busy

3 solutions

Solution 1

Solution 3

Solution 2

Add your solution here

Preview 0