Hi, it is always safe to call processEvents yourself. If the QProgressDialog has display issues it obviously does not get enough CPU to update itself, calling processEvents more often may(!!) help.
When I want to see a QProgressDialog early I normally force the issue by
calling show() immediately. That's more reliable than leaving it to the
internal heuristics. Especially if there may be a long time before the first
call to processEvents.
If you are just copying a lot of data it may be a good idea to do this in a
separate thread and just throw the updates (Qt::QueuedConnection!) to the GUI
thread from time to time. This way the GUI remains fully intact. (Hint: if you
delete objects during saving: use deleteLater; if you allocate new stuff do it
in a slot with BlockingQueuedConnection or use moveToThread).
Konrad
On Friday, Friday 15 November 2013 at 14:05, Etienne Sandré-Chardonnal wrote:
> Dear all,
>
> I have a long file saving function (gigabytes - several minutes) and I am
> trying to use QProcessDialog. I am using it the Modal way as explained in
> the documentation. However, the dialog appears after about 50 seconds,
> despite having set the minimumDuration to 0, and called setValue() several
> times before.
>
> Googling for the issue says I need to call QApplication::processEvents
> regularly in order for the GUI to refresh. However, the doc says :
>
> "If the progress dialog is modal
> (seeQProgressDialog::QProgressDialog<qthelp://com.trolltech.qt.481/qdoc/qpr
> ogressdialog.html#QProgressDialog>()), setValue()
> callsQApplication::processEvents<qthelp://com.trolltech.qt.481/qdoc/qcorea
> pplication.html#processEvents>(), so take care that this does not cause
> undesirable re-entrancy in your code"
>
> So I'm puzzled... Do I need to call it, or is it already called by
> setValue? In the example there are no explicit calls to processEvents().
>
> Qt 4.8.1
>
> Thanks!
>
> Etienne
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