Extending QML - Default Property Example

Files:

• declarative/cppextensions/referenceexamples/default/birthdayparty.cpp
• declarative/cppextensions/referenceexamples/default/birthdayparty.h
• declarative/cppextensions/referenceexamples/default/example.qml
• declarative/cppextensions/referenceexamples/default/person.cpp
• declarative/cppextensions/referenceexamples/default/person.h
• declarative/cppextensions/referenceexamples/default/main.cpp
• declarative/cppextensions/referenceexamples/default/default.pro
• declarative/cppextensions/referenceexamples/default/default.qrc

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(QDeclarativeListProperty<Person> guests READ guests)
     Q_CLASSINFO("DefaultProperty", "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 default property specifies the property to assign to whenever an explicit property is not specified, in the case of the BirthdayParty element 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.