GUI does not response when download

Posted on 2002-07-06
Last Modified: 2010-04-04
I have one application which is to download file from web.
But when it runs, the GUI sometime look like freeze and no response to my mouse click.
Even if I add some code such as application.processmessage
it is still same as above.

Can any one help me?
Question by:wangzheng
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Expert Comment

ID: 7133826

You'll have to provide more info...

Where did you put Application.Processmessage?
Is the download processed from the main thread?

Please post code example (how do you call your download
function, how does the download function looks like....)


Expert Comment

ID: 7135042
hi Wang

I think you may use a thread to download, or if you use indy, it provide an anti-fraz stuff.

Best Regards

Assisted Solution

herr_apfelschnitt earned 50 total points
ID: 7136078
You have to put the downloading code in a seperate thread. If you put it in the main VCL thread, messages can't be processed until the download is finished (if the download happens synchroneously, and that's what it looks like. if not, then this is totally useless :D ). Could you tell us HOW your program downloads the file(s)?

For more information on threads in Delphi:

Just do "New..." (at least in Delphi 3) and make a new thread object. Put the downloading code in the Execute procedure.

Btw: To cynna, I tried Application.ProcessMessages a few times, and it allows you to click buttons, but those clicks weren't actually processed (no OnClick etc. procedures executed). What does ProcessMessages actually do?

Hope this helps,
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Expert Comment

ID: 7136737
to herr_apfelschnitt :

if the code like this:

while ... do begin

the application.processmessages alow you click the button, but the OnClick event would not execute imediatly, but it would execute until the next time (or next few times) application.processmessages excuted.

Expert Comment

ID: 7137040

> ... and it allows you to click buttons, but those clicks weren't actually processed....

Your loop code didn't got around to the ProcessMessages line.
Take a look at chengjian post.

> What does ProcessMessages actually do?

Well, exactly what its name suggests :) - it makes the main VCL thread stop for a moment, take whatever message it has in a message queue, and fire a proper event for it.
Event handler code is then executed, and after it's finished, the lines after ProcessMessages are continued to be executed.

Expert Comment

ID: 7137204
I think I did put it within the loop. But I guess I probably screwed up somewhere (as I tend to do quite often :D )

Author Comment

ID: 7142423
How can I move my codes into a thread?
Because I know little about thread.
In the maim thread, I have used some VCL components, can I also use them in a thread?


Accepted Solution

Cynna earned 50 total points
ID: 7142867
wangzheng ,

> How can I move my codes into a thread?
> Because I know little about thread.

Threads can make your head hurt if you don't understand them and trying to implement them ;). I really suggest you take some time to learn about multithreading, and then get back to your project.
These are some online resources that should help enough to get you started:

* Multithreading - The Delphi Way :  <--- A MUST!

* Delphi threading by example:,1410,22411,00.html

* Better Threads For The VCL

>In the maim thread, I have used some VCL components, can I also use them in a thread?

Principally yes, but this is not a good practice. It *will* get you in trouble sooner or later.
You should always try to design your code so that the VCL operations stays separated in a main thread, and "real" processing is performed in your threads.

Expert Comment

ID: 9343098
This old question needs to be finalized -- accept an answer, split points, or get a refund.  For information on your options, please click here-> http:/help/closing.jsp#1 
Post your closing recommendations!  No comment means you don't care.

Expert Comment

by:Lukasz Lach
ID: 9460242
No comment has been added lately (18 days), so it's time to clean up this TA.
I will leave a recommendation in the Cleanup topic area for this question:

RECOMMENDATION: split points between herr_apfelschnitt http:#7136078 and Cynna http:#7142867

Please leave any comments here within 7 days.

-- Please DO NOT accept this comment as an answer ! --


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