[Development] My contribution : Extension to Qt

wim delvaux wim.delvaux at adaptiveplanet.com
Mon Jun 2 21:00:40 CEST 2014

Hi all,

I have created a extension to Qt that allows for the creation of QObject
children without the use of Q_OBJECT and moc for Qt > 5.x.

The extension does not require any changes to the Qt library.

It allows for the creation of QObject instances at runtime and thus
on-the-fly which is useful if you want to use Qt together with objects
provided by external dynamic object providers like soap or .Net or
scripting languages and that offer inspection API on those objects. The
Extension offers a framework through which the inspection API of those
external object providers can be used to feed the QMetaObject and to
generate glue code between the QObject system and the foreign object system.

I tried to make the framework as generic as possible to provide for future
versions of Qt (in fact the API was first written using Qt 4.8 but since Qt
4 was almost obsoleted I decided no longer to implement Qt 4)

The main code is small 30 KB.  The entire zip with a Qt and QML examples
just 60 K compressed.

I tried using gerrit but this is very tedious (setting up GIT, getting
access to Qt code, downloading lost of 'git' code which is not needed, etc)
I find this unnecessary as my extension compiles just like a simple Qt

this example is for the Qt C++ code

    TO= new TestObject( this ); // regular MOC-ed QObject

    connect( TO, SIGNAL( textChanged(const QString & ) ),
             ui->PropertyValue_LBL, SLOT( setText( const QString & ) ) );

    connect( this, SIGNAL( updateProperty(const QString &)),
             TO, SLOT( setTxt( const QString & ) ) );

    DynamicMetaObject::dump( TO->metaObject() );

    DTO = new DynamicTestObject( this ); // this class does not use MOC at

    connect( DTO, SIGNAL( textChanged(const QString & ) ),
             ui->PropertyValue2_LBL, SLOT( setText( const QString & ) ) );

    connect( this, SIGNAL( updateProperty2(const QString &)),
             DTO, SLOT( setTxt( const QString & ) ) );

this is a QML code snippet

    QtQuick2ApplicationViewer viewer;
    TestObject * TO = new TestObject();
    DynamicTestObject * DTO = new DynamicTestObject();

    // register some predefined objects
    QQmlContext *ctxt = viewer.rootContext();
    ctxt->setContextProperty("staticTestObject", TO );
    ctxt->setContextProperty("dynamicTestObject", DTO );


and using it from qml

        Text {
            text : "setProperty"
            MouseArea {
                anchors.fill : parent
                // activeObject is either a real MOC object or a dynamic
object ... completely transparent to QML
                onClicked : activeObject.Txt = "New property value"
        Text {
            text : "Use Dynamic Object"
            MouseArea {
                anchors.fill : parent
                onClicked : {
                    if ( parent.text == "Use Dynamic Object" ) {
                        parent.text = "Use Static Object"
                        activeObject = dynamicTestObject;
                    } else {
                        parent.text = "Use Dynamic Object"
                        activeObject = staticTestObject;

I would like to offer this code to the community.

which would be the best location for me to offer this code ?

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