[Interest] QML/C++ interaction in Qt6

[Jérôme Godbout]

Hi,

Thanks for the info, I did took a look at the QML_ELEMENT at https://www.qt.io/blog/qml-type-registration-in-qt-5.15

I was a bit confuse about how this actually do the the convertion between people and person in the following example given:



***********************

qmlRegisterType<Person>("People", 1,0, "Person");



This would register the C++ class "Person" as a QML element also called "Person", into the module "People" under the version 1.0. This line has disappeared in Qt 5.15. Instead, the following lines have been added to the adding.pro file:



CONFIG += qmltypes

QML_IMPORT_NAME = People

QML_IMPORT_MAJOR_VERSION = 1



These lines specify the import name and major version for all types exposed to QML. Finally, the most important change, is the "QML_ELEMENT" macro added to the person.h file:



class Person : public QObject

{

    Q_OBJECT

    Q_PROPERTY(QString name READ name WRITE setName)

    Q_PROPERTY(int shoeSize READ shoeSize WRITE setShoeSize)

    QML_ELEMENT

public:

    Person(QObject *parent = nullptr);

    [...]

};

***********************

how does the Person class is link to the People name exactly?!? I do not understand how can it known that the C++ class should be link the given People import name?! Is like a stack, if I change the QML_IMPORT_NAMES before using any HEADERS += or SOURCES += ? like this:



CONFIG += qmltypes

QML_IMPORT_NAME = People

QML_IMPORT_MAJOR_VERSION = 1



HEADERS += Person.h

SOURCES += Person.cpp



QML_IMPORT_NAME = MyOtherModule

QML_IMPORT_MAJOR_VERSION = 1



HEADERS += MyOtherClass.h

SOURCES += MyOtherClass.cpp



Is that how it should work? Is the order of declaration into .pro and .pri matter to make this work or there is something I don’t get here? Thanks



-----Original Message-----
From: Ulf Hermann <ulf.hermann at qt.io>
Sent: September 12, 2020 3:24 AM
To: Jérôme Godbout <godboutj at amotus.ca>; interest at qt-project.org
Subject: Re: [Interest] QML/C++ interaction in Qt6



> Will Qt 6 still use the Meta information to access Qml properties or

> it rely more on compiled C++ now? I guess it still the same as before.

> Is the properties declaration of Qt for MCU (Qml lite or soemthign

> like that) be available (syntax wise, template)? That would leverage

> soo much redundent code to expose properties with get/set and changed

> event. That will be a slim fast for code that expose to Qml (to Meta

> data actually, Qml use the meta data) and maybe event make that layer

> disapear one day.



Registration of C++ types for QML in dev is largely unchanged from 5.15.

You get the QML_ELEMENT etc. macros we introduced in 5.15 to make the registration as painless as possible. The indirection through the metatype system is necessary for the case of dynamically interpreted QML. We can generate C++ code from your QML to directly access your C++ types, but if you want to execute that same QML in interpreted mode, those C++ types need to be visible to metatype system in order to be accessible.



Also, the new property system is being introduced. If you provide a BINDABLE property, you may be able to skip the READ, WRITE, and NOTIFY methods in the future. This is still being worked on, though.



best,

Ulf
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