Using qmlscene with QObject singleton type

Sh_sch · 15 Sept 2021, 09:48

Hello,
I have a qml app which use a QObject singleton in order to use existing C++ functionnalities.
My API is defined in C++ and imported in qml as described in qmlRegisterSingletonType documentation, and it works well when I run my application.
But when I want to use qmlscene, my module is not installed, and I don't know how to import it. In the documentation, the -I argument seems only applicable to qml module (in *.qml file). Any idea on how to import C++ QObject singleton type in qmlscene ?

Thanks !

eyllanesc · S Sh_sch 15 Sept 2021, 08:48

@Sh_sch You have to create a plugin and then use the -I option.

Demo:

TEMPLATE = lib
TARGET = FooPlugin
QT += qml quick
CONFIG += plugin c++11

TARGET = $$qtLibraryTarget($$TARGET)
uri = com.mycompany.qmlcomponents

# Input
SOURCES += \
        fooplugin_plugin.cpp \
        foo.cpp

HEADERS += \
        fooplugin_plugin.h \
        foo.h

DISTFILES = qmldir

!equals(_PRO_FILE_PWD_, $$OUT_PWD) {
    copy_qmldir.target = $$OUT_PWD/qmldir
    copy_qmldir.depends = $$_PRO_FILE_PWD_/qmldir
    copy_qmldir.commands = $(COPY_FILE) "$$replace(copy_qmldir.depends, /, $$QMAKE_DIR_SEP)" "$$replace(copy_qmldir.target, /, $$QMAKE_DIR_SEP)"
    QMAKE_EXTRA_TARGETS += copy_qmldir
    PRE_TARGETDEPS += $$copy_qmldir.target
}

qmldir.files = qmldir
unix {
    installPath = $$[QT_INSTALL_QML]/$$replace(uri, \., /)
    qmldir.path = $$installPath
    target.path = $$installPath
    INSTALLS += target qmldir
}

foo.h

#ifndef FOO_H
#define FOO_H

#include <QObject>

class Foo : public QObject
{
    Q_OBJECT
    Q_DISABLE_COPY(Foo)

public:
    explicit Foo(QObject *parent = nullptr);
    ~Foo() override;
    Q_INVOKABLE QString bar() const;
};

#endif // FOO_H

#include "foo.h"

Foo::Foo(QObject *parent)
    : QObject(parent)
{
}

Foo::~Foo()
{
}

QString Foo::bar() const
{
    return "baz";
}

fooplugin_plugin.h

#ifndef FOOPLUGIN_PLUGIN_H
#define FOOPLUGIN_PLUGIN_H

#include <QQmlExtensionPlugin>

class FooPluginPlugin : public QQmlExtensionPlugin
{
    Q_OBJECT
    Q_PLUGIN_METADATA(IID QQmlExtensionInterface_iid)

public:
    void registerTypes(const char *uri) override;
};

#endif // FOOPLUGIN_PLUGIN_H

fooplugin_plugin.cpp

#include "fooplugin_plugin.h"

#include "foo.h"

#include <qqml.h>

static QObject *singletonProvider(QQmlEngine *engine, QJSEngine *scriptEngine)
{
    Q_UNUSED(engine)
    Q_UNUSED(scriptEngine)

    Foo *foo = new Foo();
    return foo;
}

void FooPluginPlugin::registerTypes(const char *uri)
{
    // @uri com.mycompany.qmlcomponents
    // qmlRegisterType<Foo>(uri, 1, 0, "Foo");
    qmlRegisterSingletonType<Foo>(uri, 1, 0, "Foo", singletonProvider);

}

So you create a folder with the following structure:

imports
└── com
    └── mycompany
        └── qmlcomponents
            ├── libFooPlugin.so
            └── qmldir

Then you import the module in your main.qml:

import QtQuick 2.15
import QtQuick.Window 2.15
import com.mycompany.qmlcomponents 1.0

Window {
    width: 640
    height: 480
    visible: true
    title: qsTr("Hello World")

    Component.onCompleted: console.log(Foo.bar())
}

And then you finally run:

qmlscene -I /path/of/imports main.qml

raven-worx · S Sh_sch 15 Sept 2021, 08:48

@Sh_sch
you need to create a QML plugin, that can be loaded by any QML application (such as qmlscene)
https://doc.qt.io/qt-5/qtqml-tutorials-extending-qml-example.html
or
https://doc.qt.io/archives/qt-5.9/qqmlextensionplugin.html

eyllanesc · S Sh_sch 15 Sept 2021, 08:48