A question on threading

[Rahul]

Hello,

I am writing a program related to image compression in C# (GUI
Application). In that I have a "heavy, long running" method which
among other things, calls this.Invalidate(); to make the screen
refresh to display the changes in image during processing.

The problem is that, once the program enters this method, the GUI
Window becomes non-responsive (but GUI gets updated regularly due to
this.Invalidate()).

So, I want the GUI to stay responsive while executing this method.

I tried running the method in another thread but then I cannot call
this.Invalidate() because "this" is in parent thread, and it throws
error.

How can I keep my window responsive while running this method? Any
ideas?

[Mugunth]

On Mar 2, 8:38 pm, Rahul <[e-mail]:

Hello,

I am writing a program related to image compression in C# (GUI
Application). In that I have a "heavy, long running" method which
among other things, calls this.Invalidate(); to make the screen
refresh to display the changes in image during processing.

The problem is that, once the program enters this method, the GUI
Window becomes non-responsive (but GUI gets updated regularly due to
this.Invalidate()).

So, I want the GUI to stay responsive while executing this method.

I tried running the method in another thread but then I cannot call
this.Invalidate() because "this" is in parent thread, and it throws
error.

How can I keep my window responsive while running this method? Any
ideas?

Try using a backgroundworker.

[Peter Webb]

"Rahul" <ra*****@gmail.comwrote in message
news:00**********************************@e6g2000p rf.googlegroups.com...

Hello,

I am writing a program related to image compression in C# (GUI
Application). In that I have a "heavy, long running" method which
among other things, calls this.Invalidate(); to make the screen
refresh to display the changes in image during processing.

The problem is that, once the program enters this method, the GUI
Window becomes non-responsive (but GUI gets updated regularly due to
this.Invalidate()).

So, I want the GUI to stay responsive while executing this method.

I tried running the method in another thread but then I cannot call
this.Invalidate() because "this" is in parent thread, and it throws
error.

How can I keep my window responsive while running this method? Any
ideas?

Application.DoEvents() will force your thread to process messages from the
UI. Its probably not the right way to do it, but it will very probably work.
Just stick it in somewhere you expect to be called at least 50 times per
second and the UI should work just fine.

[Rahul]

On Mar 2, 4:47 am, Mugunth <[e-mail]:

On Mar 2, 8:38 pm, Rahul <[e-mail]:

Hello,

I am writing a program related to image compression in C# (GUI
Application). In that I have a "heavy, long running" method which
among other things, calls this.Invalidate(); to make the screen
refresh to display the changes in image during processing.

The problem is that, once the program enters this method, the GUI
Window becomes non-responsive (but GUI gets updated regularly due to
this.Invalidate()).

So, I want the GUI to stay responsive while executing this method.

I tried running the method in another thread but then I cannot call
this.Invalidate() because "this" is in parent thread, and it throws
error.

How can I keep my window responsive while running this method? Any
ideas?

Try using a backgroundworker.

I tried to call the function through BackgroundWorker.

The "this.Invalidate()" runs properly. But this.Update() (which is the
next statement) does not work.
It throws the same exception "Cross-thread operation not valid:
Control '<FormName>' accessed from a thread other than the thread it
was created on."

this.Update() is necessary to ensure that GUI gets updated quickly, so
as to make the changes visible in pseudo-real-time.

Thanks for the reply.

Any other ideas?

[Rahul]

On Mar 2, 5:10 am, "Peter Webb" <[e-mail]>
wrote:

"Rahul" <[e-mail] in message

news:00**********************************@e6g2000p rf.googlegroups.com...

Hello,

I am writing a program related to image compression in C# (GUI
Application). In that I have a "heavy, long running" method which
among other things, calls this.Invalidate(); to make the screen
refresh to display the changes in image during processing.

The problem is that, once the program enters this method, the GUI
Window becomes non-responsive (but GUI gets updated regularly due to
this.Invalidate()).

So, I want the GUI to stay responsive while executing this method.

I tried running the method in another thread but then I cannot call
this.Invalidate() because "this" is in parent thread, and it throws
error.

How can I keep my window responsive while running this method? Any
ideas?

Application.DoEvents() will force your thread to process messages from the
UI. Its probably not the right way to do it, but it will very probably work.
Just stick it in somewhere you expect to be called at least 50 times per
second and the UI should work just fine.

Peter,

A brilliant hack!! Although this might not be the best possible way...
it gets the job done.

Unless someone suggests a more "elegant" solution, this would do just
fine.

Thanks a lot! :)

[Alfred Myers]

Hi,

The UI only should be updated by the same thread that created the Control's
windows handle.
To do that, you can use Control.Invoke which receives a delegate pointing to
the code you want to execute.
For the delegate you can use a MethodInvoker such as the following.

this.Invoke(new MethodInvoker(this.Update));

HTH
"Rahul" <ra*****@gmail.comwrote in message
news:54**********************************@s19g2000 prg.googlegroups.com...

On Mar 2, 5:10 am, "Peter Webb" <[e-mail]>
wrote:

>"Rahul" <[e-mail] in message

news:00**********************************@e6g2000 prf.googlegroups.com...

Hello,

I am writing a program related to image compression in C# (GUI
Application). In that I have a "heavy, long running" method which
among other things, calls this.Invalidate(); to make the screen
refresh to display the changes in image during processing.

The problem is that, once the program enters this method, the GUI
Window becomes non-responsive (but GUI gets updated regularly due to
this.Invalidate()).

So, I want the GUI to stay responsive while executing this method.

I tried running the method in another thread but then I cannot call
this.Invalidate() because "this" is in parent thread, and it throws
error.

How can I keep my window responsive while running this method? Any
ideas?

Application.DoEvents() will force your thread to process messages from
the
UI. Its probably not the right way to do it, but it will very probably
work.
Just stick it in somewhere you expect to be called at least 50 times per
second and the UI should work just fine.

Peter,

A brilliant hack!! Although this might not be the best possible way...
it gets the job done.

Unless someone suggests a more "elegant" solution, this would do just
fine.

Thanks a lot! :)

[Peter Duniho]

On Sun, 02 Mar 2008 05:28:01 -0800, Rahul <ra*****@gmail.comwrote:

[...]

>Application.DoEvents() will force your thread to process messages from
the
UI. [...]

Peter,

A brilliant hack!! Although this might not be the best possible way...
it gets the job done.

Unless someone suggests a more "elegant" solution, this would do just
fine.

Do NOT accept that advice. It is the worst way to deal with this issue.

As mentioned by others, you can use more appropriate techniques such as
using a BackgroundWorker in conjunction with the ProgressChanged event, or
simply calling Control.Invoke() or Control.BeginInvoke() from your worker
thread to update the UI.

Note also that there's no need to call Control.Update() directly if you're
doing things correctly. For a control where you're doing your own
painting, simply calling Invalidate() will have the intended effect, and
of course for other controls, just changing their state will result in the
control itself doing the necessary invalidation.

I've yet to see an application that call Application.DoEvents() that
wasn't just plain broken. I doubt they exist and I'm certain, given your
description, that it's absolutely the wrong way to approach the issue in
your case.

Pete

[Rahul]

On Mar 2, 6:12 am, "Alfred Myers" <[e-mail]:

Hi,

The UI only should be updated by the same thread that created the Control's
windows handle.
To do that, you can use Control.Invoke which receives a delegate pointing to
the code you want to execute.
For the delegate you can use a MethodInvoker such as the following.

this.Invoke(new MethodInvoker(this.Update));

HTH

"Rahul" <[e-mail] in message

news:54**********************************@s19g2000 prg.googlegroups.com...

On Mar 2, 5:10 am, "Peter Webb" <[e-mail]>
wrote:

"Rahul" <[e-mail] in message

>news:00**********************************@e6g2000 prf.googlegroups.com...

Hello,

I am writing a program related to image compression in C# (GUI
Application). In that I have a "heavy, long running" method which
among other things, calls this.Invalidate(); to make the screen
refresh to display the changes in image during processing.

The problem is that, once the program enters this method, the GUI
Window becomes non-responsive (but GUI gets updated regularly due to
this.Invalidate()).

So, I want the GUI to stay responsive while executing this method.

I tried running the method in another thread but then I cannot call
this.Invalidate() because "this" is in parent thread, and it throws
error.

How can I keep my window responsive while running this method? Any
ideas?

Application.DoEvents() will force your thread to process messages from
the
UI. Its probably not the right way to do it, but it will very probably
work.
Just stick it in somewhere you expect to be called at least 50 times per
second and the UI should work just fine.

Peter,

A brilliant hack!! Although this might not be the best possible way...
it gets the job done.

Unless someone suggests a more "elegant" solution, this would do just
fine.

Thanks a lot! :)

Hello Alfred,

I will definitely try this approach.

Thanks a lot.