[Qt-interest] repaint()

[Konstantin Tokarev]

21.09.2010, 16:38, "phil prentice" <philp.cheer at talktalk.net>:
> Hi everyone
>
>   I would be grateful for a little help using paintEvent(). I have an
> application that has a "Continuous Button". I have implemented the slot using
> the following basic code.
> void VIwindow::continuousSlot() // SLOT
> {
>   static bool running = false;
>   if(m_continuousButton->text() == "Stop")
>   {
>     running = false;
>     return;
>   }
>   else
>   {
>     running = true;
>     m_continuousButton->setText("Stop");
>     repaint(); // Force a direct update. Works!!!
>     for(;;)
>     {
>        // Update some widgets with data ready to be redrawn
>       repaint(); // The widgets are not being drawn????
>       // Check for stop being pressed.
>       QCoreApplication::processEvents();
>        if(!running)
>          break;
>     }
>     m_continuousButton->setText("Continuous");
>   }
> }
>
> The mechanism works very well except the repaint in the for loop does not do
> anything. I know this is probably a very basic question, but why??

Because you are wasting a lot of resources continuously calling QCoreApplication::processEvents();
Use QEventLoop to introduce pause in the cycle
Also I'd recommended you to use update() instead of repaint() in this case

--
Regards,
Konstantin