[Solved] QPrintPreviewDialog paint request purpose

YuriQ

Qt 4.8.5. I use QPrintPreviewDialog like this:

@
QPrintPreviewDialog PreviewDialog(/some arguments.../);
connect(
&PreviewDialog,
SIGNAL(paintRequested(QPrinter*)),
SLOT(onPaintRequest(QPrinter*))
);
@

How to figure out what is going on inside the onPaintRequest - actual printing or print preview generation? Maybe I must use two different onPaintRequest procedures somehow?

@
void onPaintRequest(QPrinter* pPrinter)
{
// what is going on?
}
@

raven-worx

the "docs stating":http://qt-project.org/doc/qt-4.8/qprintpreviewdialog.html#details it very clear.
The signal is emitted whenevery a preview needs to be re-/drawn. You can use the same painting mechanism you would use for actual printing.
If your printing is very complex you may want to cache your printing for preview.

YuriQ

Sorry, I didn't say enough about my goal. I need to implement different behavior for:

case 1 - actual printing
case 2 - print preview generation

But I have only one onPaintRequest handler for both cases because QPrintPreviewDialog have only 1 signal (paintRequested) for both cases.

@
void onPaintRequest(QPrinter* pPrinter)
{
bool PreviewGenerating = ? // how?

if (PriviewGenerating)
    DoSomething();
else // actual printing
    DoSomethingElse();

}
@

raven-worx

ok got ya.
The problem is that there is no clean way via the QPrinter API.
On a first glance i only found this kinda hacky/unclean way:
Save the pointer of pPrinter->paintEngine() as your preview indicator. This won't change for following preview requests.
For the actual printing another paintEngine object will be created and thus it is different.
But as said its a rather unclean/hackish way. Maybe someone else has a better idea?

YuriQ

Thank you, raven-worx, your solution is enough for me.