[Kde-accessibility] qt questions

[Pupeno]

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Short question about this.
Isn't COM (the COM you're talking about) a Microsoft technology ? Does this 
code compile or will compile in Linux ?
Thanks.

On Friday 29 November 2002 06:34, Volker Hilsheimer wrote:
> > Volker, if I have questions regarding qt and I will have a lot, should
>
> I post
>
> > them here ? cross post them to qt-interest or what do you prefeer ?
>
> Depends on how many other people are interested in the answer, I guess.
> qt-interest is not a good channel, it's to crowded and I don't read it
> regularily, so either this list, or me privately will do.
>
> > My current question is where is QFeatureListInterface ?
>
> QFeatureListInterface is a part of the QCom project, and used in the
> backend of all the plugin stuff we have in Qt to identify which plugin
> does what. It's declared in the private header qcom_p.h, and has a
> single pure virtual function
>
> virtual QStringList featureList() const = 0;
>
> It also inherits from QUnknownInterface, which handles the refcounting,
> and the interface navigation. This is identical to COM's IUnknown.
>
> > It is used in qaccessible.h:256
> > struct Q_EXPORT QAccessibleFactoryInterface : public QAccessible,
>
> public
>
> > QFeatureListInterface
> > {
> >     virtual QRESULT createAccessibleInterface( const QString &,
>
> QObject *,
>
> > QAccessibleInterface** ) = 0;
> > };
>
> We use structs because encapsulation doesn't make sense with interfaces
> (ie. every function is public by default). Otherwise structs are the
> same as classes in C++. QRESULT is a unsigned long. Possible return
> values are also defined in qcom_p.h.
> The factory interface above is what a plugin implements (and all the
> interfaces inherited, e.g. QFeatureListInterface and QUnknownInterface),
> and the plugin class is exported through a C-function
> (Q_EXPORT_COMPONENT/Q_CREATE_INSTANCE macros; you can see those in the
> plugin code I sent you).
>
> Since this is all a bit complicated, and to close to COM we decided to
> remove the QCom APIs from the public APIs before the last beta of Qt
> 3.0. All the other plugin classes are encapsulated in specialized plugin
> classes in Qt (ie. QWidgetPlugin), but under the hood they use the same
> technique.
>
> We can definitely add a QAccessiblePlugin class like that to Qt that
> makes it easier to implement accessibility plugins without having to
> fight with the details above.
>
> > which is used in
> > qaccessible.cpp:343
> > qAccessibleManager->queryInterface( mo->className(), &factory );
> >
> > qAccessibleManager is declared as:
> > static QPluginManager<QAccessibleFactoryInterface> *qAccessibleManager
>
> = 0;
>
> > and defined as:
> > qAccessibleManager = new QPluginManager<QAccessibleFactoryInterface>(
> > IID_QAccessibleFactory, QApplication::libraryPaths(), "/accessible" );
>
> The QPluginManager template opens all shared libs in the specified
> directory, and ask the plugin's exported factory interface if it
> implements the correct factory interface. If it does, it asks for the
> QFeatureListInterface, if it is implemented it calls the featureList()
> function, and from that point on the manager knows wat the factory in
> the plugin can create. If then you call
> QPluginManager::queryInterface( "feature", interface ) you get the
> correct interface for "feature", e.g. the QAccessibleInterface
> implementation for "className" without having to know which plugin
> provides it.
>
>  and what's this:
> > #ifndef IID_QAccessibleFactory
> > #define IID_QAccessibleFactory QUuid( 0x49f4c6a7, 0x412f, 0x41de,
>
> 0x9e, 0x24,
>
> > 0x64, 0x88, 0x43, 0x42, 0x1f, 0xd3 )
> > #endif ?
> > Where does those numbers come from ? what for ?
>
> This is a universally unique ID (UUID), a 128 bit value generated by a
> program "uuidgen" (part of most Linux distributions AFAIK) that is based
> on time (system clock) and space (Mac address). Every COM or QCom
> interface is associated with such an ID, and that's the only way to
> compare interfaces. E.g. the implementation of queryInterface says for
> which IDs it can return a valid interface pointer, and the caller of
> queryInterface asks whether an object implements this or that interface.
> Corba uses UUIDs for similar purposes AFAIK.
>
> Qt has a public class QUuid for those values. QUuid is the only part of
> QCom that stayed in the public API.
>
> --
> Volker

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