Read QML element size defined by anchors.fill: parent

Question

I'm writing a QML extension plugin and I'm looking for a way to access the size of the element I've just implemented.

Right now the new element (named CustomElement) can be created with any size the user wants to by defining it's width and height values, so on a QML file the user can do:

CustomElement 
{
     id: my_elem
     width: 800
     height: 600
}

But I would like to be able to retrieve the size information when the user configures the size through an anchor, like this:

Rectangle
{
    width: 800
    height: 600

    CustomElement 
    {
        id: my_elem
        anchors.fill: parent
    }
}

I have no idea how to access anchors information.

The plugin class is defined as:

class CustomElement: public QDeclarativeItem
{
    Q_OBJECT
    //Q_PROPERTY() stuff
public:
    // ...
};

In the constructor of the plugin, I set QGraphicsItem::ItemHasNoContents to false:

CustomElement::CustomElement(QDeclarativeItem* parent)
: QDeclarativeItem(parent)
{
    qDebug() << "CustomElement::CustomElement parent is:" << parent;

    setFlag(QGraphicsItem::ItemHasNoContents, false);
}

After adding the debug, I noticed that the parent is 0, which explains why I'm not able to retrieve useful information with boundingRect() and others methods. Apparently, the problem is that my plugin has no parent. How do I solve this issue?

Answer 1

Solved.

Reading When is the parent set? helped me to find what I needed to do. This plugin is a graphical component (i.e. has a visual interface) meaning it will be draw on screen at some point. When Qt finishes loading your component, it calls a method named componentComplete() to notify you of so.

All I had to do was add this method to my class definition as a public method:

virtual void componentComplete();

and implement it as:

void CustomElement::componentComplete()
{
    Q_D(CustomElement);    

    // Call superclass method to set CustomElement() parent
    QDeclarativeItem::componentComplete();   
}

Calling the method of the superclass seems to set the parent of my plugin, and this gives me access to the information set by anchors.fill: parent.

Then all I had to do retrieve this information was:

Q_Q(Video);
qDebug() << "CustomElement::play: widget size is " << q->width() << "x" << q->height();