本系列所有文章可以在這里查看[http://blog.csdn.net/cloud_castle/article/category/2123873](http://blog.csdn.net/cloud_castle/article/category/2123873) 接上文[Qt5官方demo解析集26——Extending QML - Grouped Properties Example](http://blog.csdn.net/cloud_castle/article/details/37501567) 該例子繼續在上一個例子的基礎上進行擴展，并向我們展示了向一個類型中添加附加屬性的方法。 原工程不變，我們再添加一個BirthdayPartyAttached類來為BirthdayParth類提供一個額外的屬性。 birthdayparth.h: ~~~ #ifndef BIRTHDAYPARTY_H #define BIRTHDAYPARTY_H #include <QObject> #include <QDate> #include <qqml.h> #include "person.h" class BirthdayPartyAttached : public QObject // 附加屬性類 { Q_OBJECT Q_PROPERTY(QDate rsvp READ rsvp WRITE setRsvp) // 聲明一個屬性rsvp(答復)，類型為QDate public: BirthdayPartyAttached(QObject *object); QDate rsvp() const; void setRsvp(const QDate &); private: QDate m_rsvp; }; 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; //! [static attached] static BirthdayPartyAttached *qmlAttachedProperties(QObject *); // 需要定義一個靜態函數來返回這個靜態屬性的對象 //! [static attached] private: Person *m_host; QList<Person *> m_guests; }; //! [declare attached] QML_DECLARE_TYPEINFO(BirthdayParty, QML_HAS_ATTACHED_PROPERTIES) // 利用QML_DECLARE_TYPEINFO聲明使BirthdayParty類得以支持附加屬性 //! [declare attached] #endif // BIRTHDAYPARTY_H ~~~ birthdayparty.cpp: ~~~ #include "birthdayparty.h" BirthdayPartyAttached::BirthdayPartyAttached(QObject *object) : QObject(object) { } QDate BirthdayPartyAttached::rsvp() const { return m_rsvp; } void BirthdayPartyAttached::setRsvp(const QDate &d) { m_rsvp = d; } BirthdayParty::BirthdayParty(QObject *parent) : QObject(parent), m_host(0) { } Person *BirthdayParty::host() const { return m_host; } void BirthdayParty::setHost(Person *c) { m_host = c; } QQmlListProperty<Person> BirthdayParty::guests() { return QQmlListProperty<Person>(this, m_guests); } int BirthdayParty::guestCount() const { return m_guests.count(); } Person *BirthdayParty::guest(int index) const { return m_guests.at(index); } BirthdayPartyAttached *BirthdayParty::qmlAttachedProperties(QObject *object) // 當QML聲明該附加屬性時調用這個函數，返回一個該附加屬性類的對象 { return new BirthdayPartyAttached(object); } ~~~ example.qml: ~~~ import People 1.0 import QtQuick 2.0 // For QColor //! [begin] BirthdayParty { //! [begin] //! [rsvp] Boy { name: "Robert Campbell" BirthdayParty.rsvp: "2009-07-01" // 我們使用被附加的類型名 + "." + 附加屬性來使用這個附加屬性 } //! [rsvp] // ![1] Boy { name: "Leo Hodges" shoe { size: 10; color: "black"; brand: "Reebok"; price: 59.95 } BirthdayParty.rsvp: "2009-07-06" } // ![1] host: Boy { name: "Jack Smith" shoe { size: 8; color: "blue"; brand: "Puma"; price: 19.95 } } //! [end] } //! [end] ~~~ main.cpp: ~~~ #include <QCoreApplication> #include <QQmlEngine> #include <QQmlComponent> #include <QDebug> #include "birthdayparty.h" #include "person.h" int main(int argc, char ** argv) { QCoreApplication app(argc, argv); qmlRegisterType<BirthdayPartyAttached>(); // 同樣的非實例化注冊 qmlRegisterType<BirthdayParty>("People", 1,0, "BirthdayParty"); qmlRegisterType<ShoeDescription>(); qmlRegisterType<Person>(); qmlRegisterType<Boy>("People", 1,0, "Boy"); qmlRegisterType<Girl>("People", 1,0, "Girl"); QQmlEngine engine; QQmlComponent component(&engine, QUrl("qrc:example.qml")); BirthdayParty *party = qobject_cast<BirthdayParty *>(component.create()); if (party && party->host()) { qWarning() << party->host()->name() << "is having a birthday!"; if (qobject_cast<Boy *>(party->host())) qWarning() << "He is inviting:"; else qWarning() << "She is inviting:"; for (int ii = 0; ii < party->guestCount(); ++ii) { Person *guest = party->guest(ii); //! [query rsvp] QDate rsvpDate; QObject *attached = qmlAttachedPropertiesObject<BirthdayParty>(guest, false); // 返回BirthdayParty的附加屬性對象 if (attached) rsvpDate = attached->property("rsvp").toDate(); // 由于property提取到的數據時QVariant類型的，因此需要轉換成QDate //! [query rsvp] if (rsvpDate.isNull()) qWarning() << " " << guest->name() << "RSVP date: Hasn't RSVP'd"; else qWarning() << " " << guest->name() << "RSVP date:" << qPrintable(rsvpDate.toString()); } } else { qWarning() << component.errors(); } return 0; } ~~~ 顯示結果如下：  可以看到日期的顯示亂碼。這本身不能說是代碼的問題，因為國外的日期用單純的ASCII碼足夠表示了，但是由于QDate使用本地習慣顯示時間，那么在我們這它是會帶中文的，qPrintable將QString轉成了const char*，自然也就顯示不出來了。 那解決辦法是將qPrintable(rsvpDate.toString())直接改成rsvpDate.toString()就可以了。 最后顯示如下：