Qt 5.9 | Qt QML | Qt QML Examples | Extending QML - Default Property Example

Qt 5.9.9 Reference Documentation

# 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")
      public:
          BirthdayParty(QObject *parent = 0);

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

          QQmlListProperty<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 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.

Files:

- referenceexamples/default/birthdayparty.cpp
- referenceexamples/default/birthdayparty.h
- referenceexamples/default/example.qml
- referenceexamples/default/person.cpp
- referenceexamples/default/person.h
- referenceexamples/default/main.cpp
- referenceexamples/default/default.pro
- referenceexamples/default/default.qrc