Extending QML - Object and List Property Types Example

Declare the BirthdayParty

The BirthdayParty class is declared like this:

 class BirthdayParty : public QObject
 {
     Q_OBJECT
     Q_PROPERTY(Person *host READ host WRITE setHost)
     Q_PROPERTY(QDeclarativeListProperty<Person> guests READ guests)
 public:
     BirthdayParty(QObject *parent = 0);

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

     QDeclarativeListProperty<Person> guests();
     int guestCount() const;
     Person *guest(int) const;

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

The class contains a member to store the celebrant object, and also a QList<Person *> member.

In QML, the type of a list properties - and the guests property is a list of people - are all of type QDeclarativeListProperty<T>. QDeclarativeListProperty is simple value type that contains a set of function pointers. QML calls these function pointers whenever it needs to read from, write to or otherwise interact with the list. In addition to concrete lists like the people list used in this example, the use of QDeclarativeListProperty allows for "virtual lists" and other advanced scenarios.

 Person *BirthdayParty::host() const
 {
     return m_host;
 }

 void BirthdayParty::setHost(Person *c)
 {
     m_host = c;
 }

 QDeclarativeListProperty<Person> BirthdayParty::guests()
 {
     return QDeclarativeListProperty<Person>(this, m_guests);
 }

 int BirthdayParty::guestCount() const
 {
     return m_guests.count();
 }

 Person *BirthdayParty::guest(int index) const
 {
     return m_guests.at(index);
 }