Extending QML - Default Property Example

This example builds on:

• Extending QML - Inheritance and Coercion Example
• Extending QML - Object and List Property Types Example
• Extending QML - Adding Types Example

The Default Property Example is a minor modification of the Extending QML - Inheritance and Coercion Example that simplifies the specification of a BirthdayParty through the use of a default property.

BirthdayParty {
    host: Boy {
        name: "Bob Jones"
        shoeSize: 12
    }

    Boy { name: "Leo Hodges" }
    Boy { name: "Jack Smith" }
    Girl { name: "Anne Brown" }
}

Declaring the BirthdayParty Class

The only difference between this example and the last, is the addition of the DefaultProperty class info annotation.

class BirthdayParty : public QObject
{
    Q_OBJECT
    Q_PROPERTY(Person *host READ host WRITE setHost)
    Q_PROPERTY(QQmlListProperty<Person> guests READ guests)
    Q_CLASSINFO("DefaultProperty", "guests")
    QML_ELEMENT
public:
    using QObject::QObject;

    Person *host() const;
    void setHost(Person *);

    QQmlListProperty<Person> guests();
    qsizetype guestCount() const;
    Person *guest(qsizetype) const;

private:
    Person *m_host = nullptr;
    QList<Person *> m_guests;
};

The default property specifies the property to assign to whenever an explicit property is not specified, in the case of the BirthdayParty type the guest property. It is purely a syntactic simplification, the behavior is identical to specifying the property by name, but it can add a more natural feel in many situations. The default property must be either an object or list property.

Running the Example

The main.cpp file in the example includes a simple shell application that loads and runs the QML snippet shown at the beginning of this page.

Example project @ code.qt.io