On Sunday 27 July 2003 10:34 pm, Jacob M. Burbach wrote:
On Sunday 27 July 2003 05:04 am, Phil Thompson wrote:
On Saturday 26 July 2003 9:25 pm, Jacob M. Burbach wrote:
On Saturday 26 July 2003 03:22 pm, Jacob M. Burbach wrote:
What is the proper way to remove and destroy an object from a
QWidgetStack?
I tried:
object = widgetStack.widget( objectId )
widgetStack.removeWidget( object )
del object
However it doesn't seem to call the destructor of that object,
causing a memory leak. What is the proper way to do this to make sure
the object really gets destroyed?
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Update, after doing a quick check, I see I have to call
QWidgetStack.removeChild to actually decrease the reference count
Example:
object = widgetStack.widget( objectId )
widgetStack.removeWidget( object )
widgerStack.removeChild(object)
print sys.getrefcount(object)
del object
Which says it has 2 references, one would be the object variable, so
apparently I have an extra reference laying around somewhere...
When you add a widget to a QWidgetStack ownership is transfered to C++
because the widget is re-parented and so it's C++ dtor will be called as
a consequence of the QWidgetStack's dtor being called. When ownership is
transfered, the reference count is incremented - so that, if ownership is
transfered back, the original Python object (including it's specific
type) is returned.
You might expect ownership of the widget to be transfered back to Python
when you call removeWidget(). It isn't because the widget isn't removed
from the QWidgetStack's children. Another option, other that
removeChild(), would be to reparent() the child and give it a new parent
of None.
Phil
Unfortunately calling either removeChild, or using reparent with a None
parent, both caused my app to eventually crash when exiting. Any idea what
may cause the crash? The only thing I can think of is maybe python wasn't
aware the C++ object had been destroyed, and eventually tried to call its
destructor when the app exited?
But what's causing the C++ object to be destroyed?
I did find a solution in an old post by Jim Bublitz;
Originally posted by Jim Bublitz
def removeWidget (self, w) #w is a QWidget/QObject descendant
dummy = QWidget ()
w.reparent (dummy, QPoint (0, 0))
# when dummy goes out of scope, it gets garbage collected
# along with all of it's children (and the corresponding
# C++ objects get destroyed as well)
The way Qt handles the above is different than the way
'removeChild' followed by 'del w' would work.
So now in my app I retrieve the widget from the stack, then send it to a
function like above to get destroyed. This works good, and my app doesn't
crash.
It may be worth noting, this is a KDE app, using PyQt-3.5 with PyKDE, and
the widgets stored in the stack are from KDE.
If you can produce a small, complete, PyQt only example that demonstrates the
problem, I'll have a proper look at it.
Phil
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