Get rootContext from within QQuickItem

Tom asso

Can I retrieve the root context from within a QQuickItem?
I need the root context in order to make one of my QQuickItem subclass members accessible from QML. From within a QQuickView object I can just do this:

rootContext()->setContextProperty("camera", m_camera);

But QQuickItem has no rootContext() method. Another post claimed that root context can be accessed from any QObject like this:

QQmlContext *context = qmlEngine(this)->rootContext()

However when I invoke that from my QQuickItem subclass constructor, qmlEngine() return nullptr. Moreover I can't find any documentation for method QObject::qmlEngine().

Does anyone know the proper way to do this?

Thanks

sierdzio

I think you're mixing 2 ideas: context properties and visual objects.

QQuickItem is a visual object, like Rectangle, Button etc. It makes no sense to have it as a context property!

Root context properties are never drawn on screen - they only provide property data to other (visible) QML items.

So, if you need to expose some data to QML - use QObject and set it as context property. If you want to add a custom visual element to your QML scene - use QQuickItem and register is using qmlRegisterType().

Tom asso

Thanks @sierdzio . My visual object (the QQuickItem) contains a QObject subclass instance m_camera (not a visual object), which is what I want to expose as a property to QML. How do I expose m_camera object to qml from within my QQuickItem subclass code? I need the root context in order to do that, right?

Thanks!

sierdzio

@Tom-asso said in Get rootContext from within QQuickItem:

Thanks @sierdzio . My visual object (the QQuickItem) contains a QObject subclass instance m_camera (not a visual object), which is what I want to expose as a property to QML. How do I expose m_camera object to qml from within my QQuickItem subclass code? I need the root context in order to do that, right?

No, just add a property in your QQuickItem, like this:

class YourItem : public QQuickItem
{
  Q_OBJECT
  Q_PROPERTY(ClassName* camera READ camera CONSTANT)

public:
  ClassName* camera() const { return m_camera; }
};

Then you can use it in QML as a normal property of an object:

YourItem {
  id: item
  anchors.fill: parent
}

Text {
  text: qsTr("Camera object is: " + item.camera)
}