[PyKDE] SIP automatically casting up to a QWidget

[Giovanni Bajo]

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?
-- 
Giovanni Bajo