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接上文Qt5官方demo解析集26——Extending QML - Grouped Properties Example

该例子继续在上一个例子的基础上进行扩展，并向我们展示了向一个类型中添加附加属性的方法。

原工程不变，我们再添加一个BirthdayPartyAttached类来为BirthdayParth类提供一个额外的属性。

birthdayparth.h:

#ifndef BIRTHDAYPARTY_H
#define BIRTHDAYPARTY_H

#include <QObject>
#include <QDate>
#include <qqml.h>
#include "person.h"

class BirthdayPartyAttached : public QObject           // 附加属性类
{
    Q_OBJECT
    Q_PROPERTY(QDate rsvp READ rsvp WRITE setRsvp)     // 声明一个属性rsvp(答复)，类型为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 *);  // 需要定义一个静态函数来返回这个静态属性的对象
    //! [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声明使BirthdayParty类得以支持附加属性
//! [declare attached]
#endif // BIRTHDAYPARTY_H

#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)  // 当QML声明该附加属性时调用这个函数，返回一个该附加属性类的对象
{
    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"     // 我们使用被附加的类型名 + "." + 附加属性来使用这个附加属性
    }
//! [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]

#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>();                      // 同样的非实例化注册
    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的附加属性对象

            if (attached)
                rsvpDate = attached->property("rsvp").toDate(); // 由于property提取到的数据时QVariant类型的，因此需要转换成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;
}

可以看到日期的显示乱码。这本身不能说是代码的问题，因为国外的日期用单纯的ASCII码足够表示了，但是由于QDate使用本地习惯显示时间，那么在我们这它是会带中文的，qPrintable将QString转成了const char*，自然也就显示不出来了。

那解决办法是将qPrintable(rsvpDate.toString())直接改成rsvpDate.toString()就可以了。

最后显示如下：