Sending events from Qt C++ to QML

strekazoid

After spending almost the whole day trying to figure out this I decided to post a new topic :D

Ok, here is a deal. I have an event on Qt C++ side, and I want to propagate it to QML UI. What is the proper way of doing this?

I have QML application with some engine logic on C++ side. QML app is made of QApplication and QmlApplicationViewer (generated by the project wizard):

@QScopedPointer<QApplication> app(createApplication(argc, argv));
QScopedPointer<QmlApplicationViewer> viewer(QmlApplicationViewer::create());@

One approach I found was this: http://stackoverflow.com/questions/5709820/communication-between-c-and-qml
But it doesn't work for me. This is what I tried:

@Q_DECL_EXPORT int main(int argc, char *argv[])
{
QScopedPointer<QApplication> app(createApplication(argc, argv));
QScopedPointer<QmlApplicationViewer> viewer(QmlApplicationViewer::create());

QObject *rootContext = viewer->rootContext();

PropertyListener* listener = new PropertyListener(rootContext);
viewer->rootContext()->setContextProperty("PropertyListener", listener);

// Finally launch the UI
viewer->setMainQmlFile&#40;QLatin1String("qml/RingiCall/main.qml"&#41;);
viewer->showExpanded();

// Some test code
QObject *myText = viewer->rootContext()->findChild<QObject *>(QString("nameText"));
   if (myText) { // element found
       myText->setProperty("text", QVariant(QString("Hello")));
   } else {
       qDebug() << "'myText' not found";
   }

return app->exec&#40;&#41;;

}@

I also have MainPage.qml with a Text element and objectName property set to "nameText". The thing is that findChild is unable to find anything within the declarative context. Should it even work like that or am I missing something?

shifty

Hi, I'm pretty new at this myself, but I found this page to be pretty useful for information about C++ and QML together: "Using QML Bindings in C++ Applications":http://doc.qt.nokia.com/4.7-snapshot/qtbinding.html#loading-qml-components-from-c

Hope this helps you

strekazoid

Thanks, shifty. I solved this now in a completely different manner, using this example:
http://doc.qt.nokia.com/latest/declarative-cppextensions-referenceexamples-signal.html

Here is also a nice article about events: http://doc.qt.nokia.com/latest/qmlevents.html

I've created now my own custom class, declared properties as QML properties, registered my class as a new type in QML, and finally created an object of my class in QML. After that I'm able to propagate signal from C++ to QML. It is all done pretty much according to example under first link.

In case anyone trying this, watch out for your signal method name. It should start with a small letter (not capital!). Like - void superSignal(const QString &json);

After that you'll be able to catch it in QML using onSuperSignal: {}

rishygupta

can we use or manipulate QmlApplicationViewer in any other cpp(class) rather than main?

mlong

rishygupta, you have asked this question in a number of threads, a couple of which are very old threads. Please open a separate thread for a new question and please don't duplicate your questions. Thanks.