[PyQt] PyQt4 question (follow on)

[Detlev Offenbach]

On Montag, 28. Mai 2007, Detlev Offenbach wrote:
> On Sonntag, 27. Mai 2007, Phil Thompson wrote:
> > On Sunday 27 May 2007 1:10 pm, Detlev Offenbach wrote:
> > > On Sonntag, 27. Mai 2007, Phil Thompson wrote:
> > > > On Sunday 27 May 2007 12:37 pm, Detlev Offenbach wrote:
> > > > > On Sonntag, 27. Mai 2007, Phil Thompson wrote:
> > > > > > On Sunday 27 May 2007 11:50 am, Detlev Offenbach wrote:
> > > > > > > On Sonntag, 27. Mai 2007, Phil Thompson wrote:
> > > > > > > > On Saturday 26 May 2007 9:07 pm, Detlev Offenbach wrote:
> > > > > > > > > On Samstag, 26. Mai 2007, Phil Thompson wrote:
> > > > > > > > > > On Saturday 26 May 2007 7:58 pm, Detlev Offenbach wrote:
> > > > > > > > > > > On Samstag, 26. Mai 2007, Phil Thompson wrote:
> > > > > > > > > > > > On Saturday 26 May 2007 4:52 pm, Detlev Offenbach 
wrote:
> > > > > > > > > > > > > Hi,
> > > > > > > > > > > > >
> > > > > > > > > > > > > is there a PyQt equivalent to
> > > > > > > > > > > > > "qobject_cast<T*>(object)"?
> > > > > > > > > > > >
> > > > > > > > > > > > sip.cast()?
> > > > > > > > > > > >
> > > > > > > > > > > > But it shouldn't be necessary if the sub-class
> > > > > > > > > > > > conversion code has been properly implemented.
> > > > > > > > > > >
> > > > > > > > > > > How do I do that. I haven't wrapped complicated stuff
> > > > > > > > > > > like this so far. The situation is as follows. I have
> > > > > > > > > > > the following code:
> > > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > > > self.plugins.extend(self.designer.pluginManager().insta
> > > > > > > > > > >nc es () ) for plugin in self.plugins:
> > > > > > > > > > >             if isinstance(plugin,
> > > > > > > > > > > QDesignerFormEditorPluginInterface): if not
> > > > > > > > > > > plugin.isInitialized(): plugin.initialze(self.designer)
> > > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > > > "self.designer.pluginManager().instances()" returns a
> > > > > > > > > > > list of QObject. The first if statement shall check,
> > > > > > > > > > > wether the returned QObject is of type
> > > > > > > > > > > QDesignerFormEditorPluginInterface. In C++ you would do
> > > > > > > > > > > it with code like
> > > > > > > > > > >
> > > > > > > > > > > if (
> > > > > > > > > > > (qobject_cast<QDesignerFormEditorPluginInterface*>(plug
> > > > > > > > > > >in )) )
> > > > > > > > > > >
> > > > > > > > > > > How can the problem be solved with PyQt4 and Python?
> > > > > > > > > > >
> > > > > > > > > > > Note: self.designer.pluginManager() returns an object
> > > > > > > > > > > of type QDesignerPluginManager.
> > > > > > > > > >
> > > > > > > > > > The wrapper for QDesignerFormEditorPluginInterface must
> > > > > > > > > > define some %ConvertToSubClassCode which will use RTTI
> > > > > > > > > > provided by the instance to identify the right Python
> > > > > > > > > > type object. See how PyQt does it for QObject and QEvent.
> > > > > > > > > > If the instance doesn't provide any RTTI then you're
> > > > > > > > > > stuck.
> > > > > > > > >
> > > > > > > > > Mustn't the %ConvertToSubClassCode go into the more general
> > > > > > > > > class (e.g. QObject)?
> > > > > > > >
> > > > > > > > No - just in a QObject sub-class in the module.
> > > > > > > >
> > > > > > > > > Is there a way to extend the QObject wrapper?
> > > > > > > >
> > > > > > > > That's what sip does under the covers.
> > > > > > >
> > > > > > > I am stuck at the moment due to my lack of sip know how. Below
> > > > > > > is the wrapper code in question. How does the
> > > > > > > %ConvertToSubClassCode have to be?
> > > > > > >
> > > > > > > ---------------------------------------------------------------
> > > > > > >-- -- -- -- -- -- - class QDesignerFormEditorPluginInterface {
> > > > > > >
> > > > > > > %TypeHeaderCode
> > > > > > > #include <abstractformeditorplugin.h>
> > > > > > > %End
> > > > > > >
> > > > > > > public:
> > > > > > >     virtual ~QDesignerFormEditorPluginInterface();
> > > > > > >
> > > > > > >     virtual bool isInitialized() const = 0;
> > > > > > >     virtual void initialize(QDesignerFormEditorInterface *core)
> > > > > > > = 0; virtual QAction *action() const = 0;
> > > > > > >
> > > > > > >     virtual QDesignerFormEditorInterface *core() const = 0;
> > > > > > > };
> > > > > > > ---------------------------------------------------------------
> > > > > > >-- -- -- -- -- --
> > > > > >
> > > > > > What RTTI is available for the code to determine what the class
> > > > > > really is? I can't see anything that is obviously suitable - in
> > > > > > which case you are stuck.
> > > > >
> > > > > In a C++ program one would do it with this statement
> > > > >
> > > > > qobject_cast<QDesignerFormEditorPluginInterface*>(object)
> > > > >
> > > > > where object is a pointer to a QObject. If the conversion code
> > > > > would be in QObject.sip, one could probably use the inherits()
> > > > > method of QObject.
> > > >
> > > > So that's what you put in your conversion code in your
> > > > QDesignerFormEditorPluginInterface class.
> > >
> > > I tried that before I posted to this list, but it didn't work. Phil,
> > > can you give a little help?
> >
> > Post what you tried.
>
> I tried it with the following code:
>
> %ModuleHeaderCode
> #include <qobject.h>
> %End
>
> class QDesignerFormEditorPluginInterface
> {
>
> %TypeHeaderCode
> #include <abstractformeditorplugin.h>
> %End
>
> %ConvertToSubClassCode
>     if ( (qobject_cast<QDesignerFormEditorPluginInterface*>(sipCpp)) )
>         sipClass = sipClass_QDesignerFormEditorPluginInterface;
>     else
>         sipClass = NULL;
> %End
>
> public:
>     virtual ~QDesignerFormEditorPluginInterface();
>
>     virtual bool isInitialized() const = 0;
>     virtual void initialize(QDesignerFormEditorInterface *core) = 0;
>     virtual QAction *action() const = 0;
>
>     virtual QDesignerFormEditorInterface *core() const = 0;
> };
>
> However, that code doesn't even compile because at this place,
> QDesignerFormEditorPluginInterface isn't derived from QObject. It seems,
> that this is a mixin class, that QDesignerPluginManager takes care of and
> returns a QObject.

I traced this a bit further through the Qt code and found, that the plugin is 
loaded via QPluginLoader::instance(). Here is an excerpt from the Qt docu on 
how to use such a plugin.

"The component object is a QObject. Use qobject_cast() to access interfaces 
you are interested in."

It seems, we are missing something here on the Python side.

Regards,
Detlev
-- 
Detlev Offenbach
detlev at die-offenbachs.de