[Qt-interest] Basic update() paint - more info

[Tony Rietwyk]

Phil wrote:

> On Friday 30 January 2009 10:36:11 andrew.m.goth at l-3com.com wrote:
> 
> Thanks again for your time Andy.
> 
> I've had a couple of days to think about this and to 
> experiment further and 
> now I defiantly know where the problem lies but I cannot find 
> a solution. I'm 
> back where I started; I seem to have made an error after I 
> promoted the frame 
> widget to my map class.
> 
> This is from my base class constructor:
> 
> Base::Base ( QWidget* parent, Qt::WFlags fl )
>   : QMainWindow ( parent, fl ), Ui::MainWindow()
> {
>   setupUi ( this );
> 
>   map = new Map(mapFrame);
> }
> 
> The following statement calls the map class functonX() where 
> I simply have an 
> update() statement;
> 
> map->functionX();
> 
> This triggers the paint event as I described previously; the 
> two rectangles 
> are not alternatively painted in magenta and yellow. If I 
> omit the  map = new 
> Map(mapFrame) statement and include a timer signal / update 
> slot instead in my 
> map class then the rectangles are displayed correctly. Also, 
> the window, 
> including the frame, is repainted correctly if it's resized 
> or uncovered but 
> only if I omit the Map(mapFrame) statement. This must mean 
> the the error has 
> to do with the promotion of the frame or something omited 
> from the map 
> constructor itself, perhaps.
> 
> This is the map class constructor:
> 
> Map::Map(QWidget *parent)
>  : QFrame(parent)
> 
> Does any of this make any sense at all and show where I've 
> made an error?
> 
> -- 
> Regards,
> Phil.

Hi Phil, 

Have a look at the generated _ui.h file - you should see that the map object
is being created in the setupUi routine. 

It seems you are then creating a second map object in the main window
constructor, with the first one as parent! If the second one is in front-of
of the first, then any changes to the first may not be visible - or vice
versa. 

Hope that helps, 

Tony Rietwyk