[Qt-interest] QWidget and QThread ?

[Patric]

Hm, I see. But Eric, why is that needed ? Why the data should be manipulated 
only from the main thread ?

Patric

----- Original Message ----- 
From: "Eric Clark" <eclark at ara.com>
To: <qt-interest at trolltech.com>
Sent: Friday, June 05, 2009 6:21 PM
Subject: Re: [Qt-interest] QWidget and QThread ?


> Patric,
>
> We do some similar stuff in our application. This can be pretty tricky 
> though and you need to be very careful with the functions that manipulate 
> the data. Basically, when a function needs to manipulate the QWidget's 
> data, it needs to be done from the GUI thread. Here is our approach:
>
> void Foo()
> {
>   If this is not the main thread
>   {
>     Push the call to Foo onto the GUI thread
>     Return;
>   }
>
>   // Operate on the data of the widget
> }
>
> Basically, if you have a function, Foo, that operates on the widget, when 
> the function is called, check to see if it was called from the main GUI 
> thread. If it was not, then you need to post an event to the GUI thread to 
> call this function. How you post the event is up to you. We have a special 
> Custom event to handle these calls and we also implemented a macro called 
> ThreadCheck that checks to see if the call was made on the GUI thread, and 
> if it wasn't, it posts the event to the GUI thread, and returns out of the 
> function.
>
> This approach can be somewhat tricky, and sometimes you may need to wait 
> for the event to get processed before returning from the function. If you 
> need to wait, use some kind of static or global variable that gets set 
> when the function is done running and sit in a while loop until the 
> variable says it has been called. Inside the while loop you can sleep the 
> thread periodically.
>
> Eric
>
> -----Original Message-----
> From: qt-interest-bounces at trolltech.com 
> [mailto:qt-interest-bounces at trolltech.com] On Behalf Of Patric
> Sent: Friday, June 05, 2009 5:11 AM
> To: Sean Harmer; qt-interest at trolltech.com
> Subject: Re: [Qt-interest] QWidget and QThread ?
>
> Well, I have an application. With tabs. Every tab have some fields and 
> every
> tab is different widget, created with QT Designer. I use the multiple
> inheritance approach here.
>
> The GUI is generated from the main thread. But I want the data in each tab
> (i.e. the fields in the tabs) to be managed by different threads, so the 
> GUI
> not freeze if there is a problem or a slower operation.
> And I'm wondering how to design this situation. It's all about.
>
> I didn't know I can't multiple inherite QObject.
>
> Regards,
> Patric
>
>
> ----- Original Message ----- 
> From: "Sean Harmer" <sean.harmer at maps-technology.com>
> To: <qt-interest at trolltech.com>
> Sent: Friday, June 05, 2009 1:03 PM
> Subject: Re: [Qt-interest] QWidget and QThread ?
>
>
>> Hi,
>>
>> On Friday 05 Jun 2009 10:56:35 Patric wrote:
>>> Hi all,
>>> I have a form, which i generate in a widget using the multiple
>>> inheritance
>>> approach. I need a thread that operates on the data of this widget. I'm
>>> wondering, is it a good idea to make my widget thread also (i.e. 
>>> multiple
>>> inheritance from QWidget and QThread), so it'll be more convinient to
>>> operate on the data. What do you think about it ?
>> In general no. You can only inherit from QObject once and both QWidget 
>> and
>> QThread are derived from QObject.
>>
>> Also all GUI operations must be performed in the main thread (the one in
>> which
>> QApplication lives).
>>
>> I would go even further and suggest that you redesign your application to
>> separate out the data and processing side from the GUI side. It will make
>> things cleaner in the long run.
>>
>> What is it you are trying to achieve? We may be able to give you some
>> nudges
>> in suitable directions?
>>
>> Cheers,
>>
>> Sean
>>
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