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  1. Qt
  2. QTBUG-39548

QQmlListProperty sample code from docs doesn't compile

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    Details

    • Type: Bug
    • Status: Open
    • Priority: P2: Important
    • Resolution: Unresolved
    • Affects Version/s: 5.3.0
    • Fix Version/s: None
    • Component/s: Documentation
    • Labels:
      None
    • Environment:
      - OS: Ubuntu 14.04
      - Qt: 5.3, Qt Creator 3.1.1
      - Compiler: g++ (Ubuntu 4.8.2-19ubuntu1) 4.8.2

      Description

      Sample code given in the documentation section "Exposing Attributes of C++ Types to QML" fails to compile due to wrong usage of the QQmlListProperty constructor.
      Link to the doc page: http://qt-project.org/doc/qt-5/qtqml-cppintegration-exposecppattributes.html

      This is my implementation of the given sample:

      main.cpp
      #include <QGuiApplication>
      #include <QtQuick>
      #include <QtQml>
      
      class Message : public QObject
      {
          Q_OBJECT
          Q_PROPERTY(QString author READ author WRITE setAuthor NOTIFY authorChanged)
      public:
          void setAuthor(const QString &a) {
              if (a != m_author) {
                  m_author = a;
                  emit authorChanged();
              }
          }
          QString author() const {
              return m_author;
          }
      signals:
          void authorChanged();
      private:
          QString m_author;
      };
      
      class MessageBoard : public QObject
      {
          Q_OBJECT
          Q_PROPERTY(QQmlListProperty<Message> messages READ messages)
      public:
          QQmlListProperty<Message> messages() const
          {
              return QQmlListProperty<Message>(this, 0, &MessageBoard::append_message);
          }
      
      private:
          static void append_message(QQmlListProperty<Message> *list, Message *msg)
          {
              MessageBoard *msgBoard = qobject_cast<MessageBoard *>(list->object);
              if (msg)
                  msgBoard->m_messages.append(msg);
          }
      
          QList<Message *> m_messages;
      };
      
      int main(int argc, char *argv[])
      {
          QGuiApplication app(argc, argv);
      
          qmlRegisterType<Message>();
      
          return app.exec();
      }
      
      #include "main.moc"
      

      This is the compilation error:

      main.cpp: In member function 'QQmlListProperty<Message> MessageBoard::messages() const':
      main.cpp:32:80: error: no matching function for call to 'QQmlListProperty<Message>::QQmlListProperty(const MessageBoard* const, int, void (*)(QQmlListProperty<Message>*, Message*))'
               return QQmlListProperty<Message>(this, 0, &MessageBoard::append_message);
                                                                                      ^
      main.cpp:32:80: note: candidates are:
      In file included from /opt/Qt/5.3/gcc_64/include/QtQml/qqml.h:48:0,
                       from /opt/Qt/5.3/gcc_64/include/QtQml/QtQml:9,
                       from /opt/Qt/5.3/gcc_64/include/QtQuick/QtQuickDepends:4,
                       from /opt/Qt/5.3/gcc_64/include/QtQuick/QtQuick:3,
                       from main.cpp:2:
      /opt/Qt/5.3/gcc_64/include/QtQml/qqmllist.h:73:5: note: QQmlListProperty<T>::QQmlListProperty(QObject*, void*, QQmlListProperty<T>::CountFunction, QQmlListProperty<T>::AtFunction) [with T = Message; QQmlListProperty<T>::CountFunction = int (*)(QQmlListProperty<Message>*); QQmlListProperty<T>::AtFunction = Message* (*)(QQmlListProperty<Message>*, int)]
           QQmlListProperty(QObject *o, void *d, CountFunction c, AtFunction t)
           ^
      /opt/Qt/5.3/gcc_64/include/QtQml/qqmllist.h:73:5: note:   candidate expects 4 arguments, 3 provided
      /opt/Qt/5.3/gcc_64/include/QtQml/qqmllist.h:70:5: note: QQmlListProperty<T>::QQmlListProperty(QObject*, void*, QQmlListProperty<T>::AppendFunction, QQmlListProperty<T>::CountFunction, QQmlListProperty<T>::AtFunction, QQmlListProperty<T>::ClearFunction) [with T = Message; QQmlListProperty<T>::AppendFunction = void (*)(QQmlListProperty<Message>*, Message*); QQmlListProperty<T>::CountFunction = int (*)(QQmlListProperty<Message>*); QQmlListProperty<T>::AtFunction = Message* (*)(QQmlListProperty<Message>*, int); QQmlListProperty<T>::ClearFunction = void (*)(QQmlListProperty<Message>*)]
           QQmlListProperty(QObject *o, void *d, AppendFunction a, CountFunction c, AtFunction t,
           ^
      /opt/Qt/5.3/gcc_64/include/QtQml/qqmllist.h:70:5: note:   candidate expects 6 arguments, 3 provided
      /opt/Qt/5.3/gcc_64/include/QtQml/qqmllist.h:67:5: note: QQmlListProperty<T>::QQmlListProperty(QObject*, QList<T*>&) [with T = Message]
           QQmlListProperty(QObject *o, QList<T *> &list)
           ^
      /opt/Qt/5.3/gcc_64/include/QtQml/qqmllist.h:67:5: note:   candidate expects 2 arguments, 3 provided
      /opt/Qt/5.3/gcc_64/include/QtQml/qqmllist.h:65:5: note: QQmlListProperty<T>::QQmlListProperty() [with T = Message]
           QQmlListProperty()
           ^
      /opt/Qt/5.3/gcc_64/include/QtQml/qqmllist.h:65:5: note:   candidate expects 0 arguments, 3 provided
      /opt/Qt/5.3/gcc_64/include/QtQml/qqmllist.h:58:7: note: QQmlListProperty<Message>::QQmlListProperty(const QQmlListProperty<Message>&)
       class QQmlListProperty {
             ^
      /opt/Qt/5.3/gcc_64/include/QtQml/qqmllist.h:58:7: note:   candidate expects 1 argument, 3 provided
      main.cpp:33:5: warning: control reaches end of non-void function [-Wreturn-type]
           }
           ^
      make: *** [main.o] Error 1
      13:53:17: The process "/usr/bin/make" exited with code 2.
      Error while building/deploying project QtQQmlListProperty2 (kit: Desktop Qt 5.3.0 GCC 64bit)
      When executing step 'Make'
      

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            Assignee:
            docteam Qt Documentation Team
            Reporter:
            oneorjuan Juan Navarro
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              Updated:

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