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How to access qml object from one C++ extensionplugin



  • I just try the following code in my extensionplugin:
    @class QExampleQmlPlugin : public QQmlExtensionPlugin
    {
    Q_OBJECT
    Q_PLUGIN_METADATA(IID "org.qt-project.Qt.QQmlExtensionInterface")

    public:

    void registerTypes(const char *uri) {
    qmlRegisterType<ClickHandler>(uri, 1, 0, "MyClick");
    QString str = objectName();
    QObject * p = parent();
    // QString str2 = p->objectName();
    int i = 0;
    }

    void initializeEngine(QQmlEngine * engine, const char * uri) {
    QQmlApplicationEngine* app_engine = qobject_cast<QQmlApplicationEngine*>(engine);
    QList<QObject *> roots = app_engine->rootObjects();
    int i = 0;
    }
    };
    @

    but the roots is empty:
    @(gdb) p roots
    $1 = {{p = {static shared_null = {ref = {atomic = {_q_value = -1}}, alloc = 0, begin = 0, end = 0, array = {0x0}}, d = 0x7ffff6355da0 QListData::shared_null}, d = 0x7ffff6355da0 QListData::shared_null}}
    (gdb) [Thread 0x7fffe2304700 (LWP 19788) exited]@

    In my main app project, in main.cpp file, I use QQmlApplicationEngine to load main.qml file, in main.qml file, I load my plugin. Code snippet from main.cpp
    @ QQmlApplicationEngine engine;
    engine.addImportPath(imports_dir_path);
    engine.load(QUrl("qrc:/qmls/main.qml"));

    QObject * topLevel = engine.rootObjects().value(0);
    QQuickWindow * window = qobject_cast<QQuickWindow*>(topLevel);
    if (!window) {
      qWarning("Error: Your root item has to be a Window.");
      return -1;
    }
    window->showMaximized();
    return app->exec&#40;&#41;;@
    

    code from main.qml
    @import demo 1.0 // import types from the plugin
    import QtQuick.Window 2.1
    import QtQuick.Controls 1.1
    import QtQuick.XmlListModel 2.0
    import QtQuick 2.2

    // this class is defined in QML (imports/demo/hello.qml)
    Window {
    Hello {
    // this class is defined in C++ (plugin.cpp)
    MyClick {
    id: click
    }

        Text {
            text: click.value
        }
    }
    

    }@


  • Qt Champions 2017

    How and where are you calling initializeEngine ?



  • My class is a sub-class of QQmlExtensionPlugin
    initializeEngine is a virtual method inherited from QQmlExtensionPlugin class.
    After testing this, I find this method will be called by Qt while my extensionplugin is loaded by qml.


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