Qt-interest Archive, June 2007
QPalette + NColorGroups question
Message 1 in thread
Hi all,
I have come across the following QT code ...
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
QPalette palSelected;
QPalette palNormal;
...
class KTPushButton : public QPushButton
{
public:
KTPushButton(QWidget * parent)
: QPushButton(parent), isSelected(false), isDirty(false)
{
updatePalette();
}
void updatePalette()
{
palNormal = ((QWidget *)parent())->palette();
palSelected = palNormal;
for(int cg = (int) QPalette::Disabled; cg < (int)
QPalette::NColorGroups; cg++)
.....
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
I can't get my head around ....
palSelected = (QWidget *)parent())->palette();
I just don't see how the above works (though it does :)) Not sure if
its my misunderstanding of C++ or QT. I would have thought it should
be more like ... (or am I missing the point ?)
palSelected = parent->palette();
Also ...
What does QPalette::NColorGroups return ... the number of color groups
availiable ? If so
for(int cg = (int) QPalette::Disabled; cg < (int)
QPalette::NColorGroups; cg++)
counts from (int) QPalette::Disabled - that will be a 1 to number of
color groups ?
Cheers, still learning :)
Dave
--
[ signature omitted ]
Message 2 in thread
On 17.06.07 14:57:49, dave selby wrote:
> QPalette palNormal;
> ...
>
> class KTPushButton : public QPushButton
> {
> public:
> KTPushButton(QWidget * parent)
> : QPushButton(parent), isSelected(false), isDirty(false)
> {
> updatePalette();
> }
>
> void updatePalette()
> {
> palNormal = ((QWidget *)parent())->palette();
> palSelected = palNormal;
> for(int cg = (int) QPalette::Disabled; cg < (int)
> QPalette::NColorGroups; cg++)
> .....
> ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
>
> I can't get my head around ....
>
> palSelected = (QWidget *)parent())->palette();
>
> I just don't see how the above works (though it does :)) Not sure if
> its my misunderstanding of C++ or QT. I would have thought it should
> be more like ... (or am I missing the point ?)
>
> palSelected = parent->palette();
See the API docs, parent() returns a QObject, so you need a cast to
QWidget. Although the above c-cast is bad, its better to use static_cast
or dynamic_cast.
> What does QPalette::NColorGroups return ... the number of color groups
> availiable ? If so
>
> for(int cg = (int) QPalette::Disabled; cg < (int)
> QPalette::NColorGroups; cg++)
>
> counts from (int) QPalette::Disabled - that will be a 1 to number of
> color groups ?
Right.
Andreas
--
[ signature omitted ]
Message 3 in thread
On 17/06/07, Andreas Pakulat <apaku@xxxxxx> wrote:
> On 17.06.07 14:57:49, dave selby wrote:
> > QPalette palNormal;
> > ...
> >
> > class KTPushButton : public QPushButton
> > {
> > public:
> > KTPushButton(QWidget * parent)
> > : QPushButton(parent), isSelected(false), isDirty(false)
> > {
> > updatePalette();
> > }
> >
> > void updatePalette()
> > {
> > palNormal = ((QWidget *)parent())->palette();
> > palSelected = palNormal;
> > for(int cg = (int) QPalette::Disabled; cg < (int)
> > QPalette::NColorGroups; cg++)
> > .....
> > ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
> >
> > I can't get my head around ....
> >
> > palSelected = (QWidget *)parent())->palette();
> >
> > I just don't see how the above works (though it does :)) Not sure if
> > its my misunderstanding of C++ or QT. I would have thought it should
> > be more like ... (or am I missing the point ?)
> >
> > palSelected = parent->palette();
>
> See the API docs, parent() returns a QObject, so you need a cast to
> QWidget. Although the above c-cast is bad, its better to use static_cast
> or dynamic_cast.
>
Ahhh ... penny drops :) thank you :)
> > What does QPalette::NColorGroups return ... the number of color groups
> > availiable ? If so
> >
> > for(int cg = (int) QPalette::Disabled; cg < (int)
> > QPalette::NColorGroups; cg++)
> >
> > counts from (int) QPalette::Disabled - that will be a 1 to number of
> > color groups ?
>
> Right.
:)
>
> Andreas
>
And everything gets a bit clearer.
Cheers
Dave
> --
> You need more time; and you probably always will.
>
> --
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>
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[ signature omitted ]
Message 4 in thread
> > > What does QPalette::NColorGroups return ... the number of color
groups
> > > availiable ? If so
> > >
> > > for(int cg = (int) QPalette::Disabled; cg < (int)
> > > QPalette::NColorGroups; cg++)
> > >
> > > counts from (int) QPalette::Disabled - that will be a 1 to number
of
> > > color groups ?
> >
> > Right.
>
> :)
>
> >
> > Andreas
> >
>
One thing of note... QPalette::NColorGroups does not "return" the number
of color groups... it IS the number of color groups... There is no
function stack for the call QPalette::NColorGroups
Scott
--
[ signature omitted ]
Message 5 in thread
On 6/17/07, Andreas Pakulat <apaku@xxxxxx> wrote:
>
> On 17.06.07 14:57:49, dave selby wrote:
> > QPalette palNormal;
> > ...
> >
> > class KTPushButton : public QPushButton
> > {
> > public:
> > KTPushButton(QWidget * parent)
> > : QPushButton(parent), isSelected(false), isDirty(false)
> > {
> > updatePalette();
> > }
> >
> > void updatePalette()
> > {
> > palNormal = ((QWidget *)parent())->palette();
> > palSelected = palNormal;
> > for(int cg = (int) QPalette::Disabled; cg < (int)
> > QPalette::NColorGroups; cg++)
> > .....
> >
> ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
> >
> > I can't get my head around ....
> >
> > palSelected = (QWidget *)parent())->palette();
> >
> > I just don't see how the above works (though it does :)) Not sure if
> > its my misunderstanding of C++ or QT. I would have thought it should
> > be more like ... (or am I missing the point ?)
> >
> > palSelected = parent->palette();
>
> See the API docs, parent() returns a QObject, so you need a cast to
> QWidget. Although the above c-cast is bad, its better to use static_cast
> or dynamic_cast.
Even better would be to use QWidget::parentWidget(), which works like
QObject::parent() but returns a QWidget*.
Tom
