QML C++ Goodbye World

Question

I created an Hello World app in QML. Now I want to learn how to modify the text from "Hello World" to "Goodbye World" from C++.

The qml looks like so:

import QtQuick 2.6

Rectangle {
    property alias mouseArea: mouseArea

    width: 360
    height: 360

    MouseArea {
        id: mouseArea
        anchors.fill: parent
    }

    Text {
        id: helloText
        anchors.centerIn: parent
        text: "Hello World"
    }
}

I've attempted to follow the

https://wiki.qt.io/Introduction_to_Qt_Quick#Integration_with_C.2B.2B_applications

But no luck. The code seems incomplete. For example, it leaves off information with ellipses like so:

QDeclarativeContext *context = …;

And I can't find the header for the QDeclarativeContext even if it didn't. I suspect the documentation is old, but I'm not sure.

Anyway, I just want to see a simple example that lets me change the text from "Hello World" to "Goodbye World" from inside a C++ program.

Answer 1

That code is for the old QtQuick1 API, which was based on QGraphicsScene and is now outdated, obsolete and IIRC removed from Qt.

I would recommend against mingling with QML from C++, I'd even go further and call it an anti-pattern, in 99.9999% of the cases there is a better solution. You should keep the interaction between C++ and QML to a well defined API.

That being said, it is still possible to find objects and manipulate their properties. You can use QQmlApplicationEngine::rootObjects() to get access to the root objects, from there you can findChild() any object you have provided a objectName on the QML side, you can use QMetaObject:invokeMethod() (works for QML functions too!), use qobject_cast, set properties and whatnot.

All those techniques are covered in the documentation.