[PyKDE] SIP automatically casting up to a QWidget

[Paul Giannaros]

On Thursday 22 February 2007 17:10, Giovanni Bajo wrote:
> On 2/22/2007 5:32 PM, Paul Giannaros wrote:
> >>> I have a class A that i'm wrapping with SIP. The class inherits from a
> >>> bunch of other classes. One of the classes it inherits from also in
> >>> turn inherits from QWidget. When I import the created module, whenever
> >>> I call a method that is meant to return an instance of class A I get a
> >>> QWidget instead. I can use sip.cast to get the QWidget back to an A
> >>> instance, but that's not a very friendly solution.
> >>> Can someone suggest why this is happening, or how to fix it?
> >>
> >> SIP needs to know the correct run-time type of your class: otherwise
> >> when it receives a QWidget* it cannot know what type the class really
> >> is.
> >>
> >> Have a look at how %ConvertToSubClassCode is implemented in
> >> QtCore/qobject.sip and QtGui/qapplication.sip (assuming you're using
> >> Qt4). Within your a.sip, you must add your own %ConvertToSubClassCode
> >> that verifies if a generic QObject* is an instance of your type (class
> >> A). SIP then knows how to "chain" all the other %ConvertToSubClassCode
> >> in the object hierarchy, so your code needs only to verify your own
> >> class.
> >
> > But I don't see why it's receiving a QWidget* -- the return type of the
> > functions i'm calling are explicitly A*.
>
> Because elsewhere, in a point of your code that you are probably
> ignoring, the instance is being returned as QWidget*. SIP executes the
> %ConvertToSubClassCode *once* and create a Python object of type
> QWidget; it register this Python an object within a hash table. After
> that, every time the instance is returned by *any* method, it's looked
> up in the hash table, and the Python wrapper (already constructed) is
> found.
>
> > Nevertheless, I implemented %ConvertToSubClassCode in class A (and class
> > B which inherits QWidget) using
> > sipMapStringToClass/sipStringTypeClassMap, and a QWidget is still being
> > returned.
>
> Can you show us this code please?

Sure, attached.
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