Qt Reference Documentation

# 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.