Qt-interest Archive, February 2007
The case of the disappearing widget
Message 1 in thread
I am having some trouble displaying plain QWidget with a color as a child of another. Below is a simple reproducer of the problem (a test program I created):
class MyWin: public QWidget
{
Q_OBJECT
public:
MyWin(QWidget *parent = NULL)
:
QWidget(parent)
{
QPalette palette;
palette.setColor(QPalette::Window, QColor("white"));
palette.setColor(QPalette::WindowText, QColor("black"));
setPalette(palette);
resize(300, 300);
QWidget *wid= new QWidget(this);
palette = wid->palette();
palette.setColor(QPalette::Window, QColor("red"));
palette.setColor(QPalette::WindowText, QColor("white"));
wid->setPalette(palette);
wid->resize(100, 100);
wid->move(20, 20);
QLabel *label = new QLabel("This is a label", wid);
label->move(2, 2);
}
};
The second QWidget briefly flashes, then disappears... Why?
Below is main:
int main(int argc, char **argv)
{
QApplication app(argc, argv);
MyWin win;
win.show();
return app.exec();
}
Thanks in advance,
Susan
_____________________________
Susan Macchia
mailto:susan@xxxxxxxxxxxx
http://www.smacchia.net
_____________________________
Message 2 in thread
On Tuesday 27 February 2007 14:35, Susan Macchia wrote:
> I am having some trouble displaying plain QWidget with a color as a child
> of another. Below is a simple reproducer of the problem (a test program I
> created):
>
> class MyWin: public QWidget
> {
> Q_OBJECT
>
> public:
> MyWin(QWidget *parent = NULL)
>
> QWidget(parent)
> {
> QPalette palette;
> palette.setColor(QPalette::Window, QColor("white"));
> palette.setColor(QPalette::WindowText, QColor("black"));
> setPalette(palette);
> resize(300, 300);
>
>
> QWidget *wid= new QWidget(this);
>
> palette = wid->palette();
> palette.setColor(QPalette::Window, QColor("red"));
> palette.setColor(QPalette::WindowText, QColor("white"));
> wid->setPalette(palette);
> wid->resize(100, 100);
> wid->move(20, 20);
>
> QLabel *label = new QLabel("This is a label", wid);
> label->move(2, 2);
> }
> };
>
>
>
> The second QWidget briefly flashes, then disappears... Why?
>
> Below is main:
>
> int main(int argc, char **argv)
> {
> QApplication app(argc, argv);
>
> MyWin win;
> win.show();
> return app.exec();
> }
>
>
>
>
> Thanks in advance,
> Susan
You forgot to set the main widget. QApplication::setMainWidget() or some
such.
--
[ signature omitted ]
Message 3 in thread
> I am having some trouble displaying plain QWidget with a color as a child of
> another. Below is a simple reproducer of the problem (a test program I created):
Susan, I ran into this exact same problem with some QPushButtons in an app I was
playing around with a few months ago. It turns out that you have to set the palette
parameters in a very specific way (unfortunately, I don't remember what I did).
To figure it out, I fired up Qt designer and put a couple of frames and labels
together using the same palette options I was doing in my code. Then I used Ctrl-R
to actually preview them and sure enough I would see the "flash" and the colors
would disappear. After a few iterations of palette options, I was able to make it
work. I remember the solution being pretty unexpected.
Hope that helps some,
Caleb
--
[ signature omitted ]
Message 4 in thread
Chris Thompson wrote:
>On Tuesday 27 February 2007 14:35, Susan Macchia wrote:
>> I am having some trouble displaying plain QWidget with a color as a child
>> of another. Below is a simple reproducer of the problem (a test program I
>> created):
>>
>> class MyWin: public QWidget
>> {
>> Q_OBJECT
>>
>> public:
>> MyWin(QWidget *parent = NULL)
>>
>> QWidget(parent)
>> {
>> QPalette palette;
>> palette.setColor(QPalette::Window, QColor("white"));
>> palette.setColor(QPalette::WindowText, QColor("black"));
>> setPalette(palette);
>> resize(300, 300);
>>
>>
>> QWidget *wid= new QWidget(this);
>>
>> palette = wid->palette();
>> palette.setColor(QPalette::Window, QColor("red"));
>> palette.setColor(QPalette::WindowText, QColor("white"));
>> wid->setPalette(palette);
>> wid->resize(100, 100);
>> wid->move(20, 20);
>>
>> QLabel *label = new QLabel("This is a label", wid);
>> label->move(2, 2);
>> }
>> };
>>
>>
>>
>> The second QWidget briefly flashes, then disappears... Why?
>>
>> Below is main:
>>
>> int main(int argc, char **argv)
>> {
>> QApplication app(argc, argv);
>>
>> MyWin win;
>> win.show();
>> return app.exec();
>> }
>>
>>
>>
>>
>> Thanks in advance,
>> Susan
>
>You forgot to set the main widget. QApplication::setMainWidget() or some
>such.
Hmm - I've never *had* to do that. The examples in the Qt book also don't always show doing this. But I can give it a try. Note that The main widget "win" does show up...
--
[ signature omitted ]
Message 5 in thread
On Tuesday 27 February 2007 15:29, susan@xxxxxxxxxxxx wrote:
> Chris Thompson wrote:
> >On Tuesday 27 February 2007 14:35, Susan Macchia wrote:
> >> I am having some trouble displaying plain QWidget with a color as a
> >> child of another. Below is a simple reproducer of the problem (a test
> >> program I created):
> >>
> >> class MyWin: public QWidget
> >> {
> >> Q_OBJECT
> >>
> >> public:
> >> MyWin(QWidget *parent = NULL)
> >>
> >> QWidget(parent)
> >> {
> >> QPalette palette;
> >> palette.setColor(QPalette::Window, QColor("white"));
> >> palette.setColor(QPalette::WindowText, QColor("black"));
> >> setPalette(palette);
> >> resize(300, 300);
> >>
> >>
> >> QWidget *wid= new QWidget(this);
> >>
> >> palette = wid->palette();
> >> palette.setColor(QPalette::Window, QColor("red"));
> >> palette.setColor(QPalette::WindowText, QColor("white"));
> >> wid->setPalette(palette);
> >> wid->resize(100, 100);
> >> wid->move(20, 20);
> >>
> >> QLabel *label = new QLabel("This is a label", wid);
> >> label->move(2, 2);
> >> }
> >> };
> >>
> >>
> >>
> >> The second QWidget briefly flashes, then disappears... Why?
> >>
> >> Below is main:
> >>
> >> int main(int argc, char **argv)
> >> {
> >> QApplication app(argc, argv);
> >>
> >> MyWin win;
> >> win.show();
> >> return app.exec();
> >> }
> >>
> >>
> >>
> >>
> >> Thanks in advance,
> >> Susan
> >
> >You forgot to set the main widget. QApplication::setMainWidget() or some
> >such.
>
> Hmm - I've never *had* to do that. The examples in the Qt book also don't
> always show doing this. But I can give it a try. Note that The main
> widget "win" does show up...
Sorry, I was probably thinking of something else.
--
[ signature omitted ]
Message 6 in thread
>> I am having some trouble displaying plain QWidget with a color as a child of
>> another. Below is a simple reproducer of the problem (a test program
>>I created):
>
>Susan, I ran into this exact same problem with some QPushButtons in an app I was
>playing around with a few months ago. It turns out that you have to set the palette
>parameters in a very specific way (unfortunately, I don't remember what I did).
>
>To figure it out, I fired up Qt designer and put a couple of frames and labels
>together using the same palette options I was doing in my code. Then I used Ctrl-R
>to actually preview them and sure enough I would see the "flash" and the colors
>would disappear. After a few iterations of palette options, I was able to make it
>work. I remember the solution being pretty unexpected.
>
>Hope that helps some,
>Caleb
Thanks, I'll give that a try. Pretty weird though. I assume your think that my setting the palette of the child widget is the culprit? Or is it also the top level widget?
-- Susan
--
[ signature omitted ]
Message 7 in thread
>
> Thanks, I'll give that a try. Pretty weird though. I assume your
> think that my setting the palette of the child widget is the
> culprit? Or is it also the top level widget?
>
> -- Susan
Correct on the child widget. I'm used to thinking the way of Qt3
where you have foreground and background colors instead of color
roles. I was setting the button text color and the "window" color
and I could see it reflect on the buttons for a split second before
reverting to the color of the parent widget. There was some kind of
palette trickery involved, but I sure don't remember the specifics.
Caleb
--
[ signature omitted ]
