refreshing labels

[ht1]

Hi,

I was wondering why my label does not automatically update while this is running:



for (int kk=1; kk<100; kk++)
{
//main code is here
Label->setNum(kk);
}

Label is a QLabel declared elsewhere

I'd like to see the numbers counted between 1 and 99 but the only number I see is 99 (when the program is complete). Why don't I see other numbers sequentially on the screen. Is it because labels can be refreshed only when control is returned to main()?
Can labels be refreshed while another function is running?

[marcel]

You set the numbers too fast. The label doesn't get the chance to update.
You should use a QTimer with an interval of 100-200ms. Connect its timeout signal to a slot in which you update the label with a new value. Then you will be able to see something.

[ht1]

Thanks Marcel, but I think something else than speed is the problem.
The code that I designated as (//main code here) is very long and takes a long time to compile. The labels have about a minute to refresh. Maybe the labels don't refresh because the processor is 100% busy with doing the math?

[jacek]

Maybe the labels don't refresh because the processor is 100% busy with doing the math?
Yes, you block the Qt's event loop and Qt can't redraw anything or even process user's input. You can avoid this by invoking QCoreApplication::processEvents() from time to time or using QTimer to drive your loop. A third option is to move those computations to a thread.

[jpn]

In other words, events don't get processed during a busy loop. When you change the contents of a label, a few events get scheduled (to update the label). But no event reaches its receiver until you return the control to the event loop. One simple but a bit ugly solution is to force the application to process its events:


for (int kk=1; kk<100; kk++)
{
//main code is here
Label->setNum(kk);
QApplication::processEvents(); // <--
}