Access QML root object from C++ QML type

Question

I have a custom QML type written in C++, the classname is MyCustomType and it's located in the files mycustomtype.h and mycustomtype.cpp.

In the main.cpp file the QML type is made available:

qmlRegisterType<MyCustomType>("MyCustomType", 1, 0, "MyCustomType");

QQmlApplicationEngine engine;
engine.load(QUrl(QStringLiteral("../qml/main.qml")));

In the main.cpp file I can get access to the engine's root object like this:

rootObject = static_cast<QQuickWindow *> (engine.rootObjects().first());

My issue is that I need access to that rootObject from within the MyCustomType class in the mycustomtype.cpp file. Is that possible?

The only way I could think of was to pass the rootObject to the constructor. But since the MyCustomType is instatiated in the QML document, and not in C++ code, this solution won't work.

Any ideas?

Why do you need to access to the root object? This will help to answer your question. Do you need access to the parent of your object? A set of properties you added in the root object ? Access to the application window? Ability to call signal or functions of the root? etc. — GrecKo
The MyCustomType is setting up a video stream using GStreamer and I need to start the pipeline using the method scheduleRenderJob from the rootObject (QQuickWindow). — KMK
If your type is a QQuickItem you can use QQuickItem::window() to access the window where the item is rendered. — GrecKo

KMK KMK · Accepted Answer · 2017-12-05T10:15:25

I found a solution based on GrecKo's comment.

Instead of making MyCustomType extend QObject, I made it extend QQuickItem. Then it's possible to call window() from anywhere in that class and get the root object. This is simple and it works.

mycustomtype.h:

class MyCustomType : public QQuickItem
{
    Q_OBJECT

public:
    explicit MyCustomType(QQuickItem *parent = 0);

}

mycustomtype.cpp

MyCustomType::MyCustomType(QQuickItem *parent) : QQuickItem(parent)
{
    QQuickWindow *rootObject = window();    
}

Access QML root object from C++ QML type

2 Answers