[PyKDE] SIP automatically casting up to a QWidget
newellm at blur.com
Thu Feb 22 16:33:47 GMT 2007
On Thursday 22 February 2007 06:32, Phil Thompson wrote:
> On Thursday 22 February 2007 1:53 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?
> You need to implement %ConvertToSubClassCode that handles A (and any other
> QObject derived classes in your module).
While I understand the use of %ConvertToSubClassCode, it seems to me that it
should not be required for this case. If the class hierarchy is
QWidget -> A
and the function signature already shows that the function returns class A,
why should convertSubClass ever convert it to a QWidget?
I changed my sip a while ago for this case, since I have many Dialogs and
widgets wrapped with sip that I don't really need automatic converters for,
but don't want them downgraded to a QWidget when they are constructed.
Here's the code I have inside the while loop in convertToSubClass.
* The base type is the "root" class that may have a number of
* convertors each handling a "branch" of the derived tree of
* classes. The "root" normally implements the base function that
* provides the RTTI used by the convertors and is re-implemented
* by derived classes. We therefore see if the target type is a
* sub-class of the root, ie. see if the convertor might be able to
* convert the target type to something more specific.
if (PyType_IsSubtype((PyTypeObject *)type, (PyTypeObject *)scc->scc_basetype))
subtype = (*scc->scc_convertor)(cppPtr);
* Because a base module with convertToSubClass code may know how to convert
* A -> B -> C
* a derived module may have a class D that inherits from C,
* so the base module may believe it is converting to a more specific type
* by converting to C, when in fact D is already the most specific type.
if (subtype && !PyType_IsSubtype((PyTypeObject*)type,
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