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接上文Qt5官方demo解析集27——Extending
QML - Attached Properties Example

这个demo演示了为QML自己定义类型加入信号的方法。这与Qt5官方demo解析集16——Chapter
2: Connecting to C++ Methods and Signals所介绍的差点儿相同。鉴于样例的尺寸，可能那一篇要更清晰一些。

不管怎样，我们还是要继续扩展这个BirthdayParty例程。我们为这个生日派对加入了一个“派对開始”的信号，并定义了一个函数用来发射这个信号。

因为person类依旧没有改变。我们看看小小修改了的birthdayparty.h:

#ifndef BIRTHDAYPARTY_H

#define BIRTHDAYPARTY_H

#include <QObject>

#include <QDate>

#include <qqml.h>

#include "person.h"

class BirthdayPartyAttached : public QObject

{

    Q_OBJECT

    Q_PROPERTY(QDate rsvp READ rsvp WRITE setRsvp)

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 BirthdayPartyAttached *qmlAttachedProperties(QObject *);

    void startParty();                       // 自己定义函数，之所以不使用Q_INVOKABLE是由于该函数是在main.cpp而不是QML中被调用的

// ![0]

signals:

    void partyStarted(const QTime &time);   // 自己定义信号

// ![0]

private:

    Person *m_host;

    QList<Person *> m_guests;

};

QML_DECLARE_TYPEINFO(BirthdayParty, QML_HAS_ATTACHED_PROPERTIES)

#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);

}

void BirthdayParty::startParty()        // 该函数用来将当前时间作为信号參数发射出去

{

    QTime time = QTime::currentTime();

    emit partyStarted(time);

}

BirthdayPartyAttached *BirthdayParty::qmlAttachedProperties(QObject *object)

{

    return new BirthdayPartyAttached(object);

}

example.qml:

import People 1.0

import QtQuick 2.0  // For QColor

BirthdayParty {

// ![0]

    onPartyStarted: console.log("This party started rockin' at " + time); // 在QML中我们不须要额外对信号进行处理

// ![0]                                                                   // 仅仅须要关注与该信号相应的onXXX函数

                                                                          // 当信号发出时该函数即被运行

    host: Boy {

        name: "Bob Jones"

        shoe { size: 12; color: "white"; brand: "Nike"; price: 90.0 }

    }

    Boy {

        name: "Leo Hodges"

        BirthdayParty.rsvp: "2009-07-06"

        shoe { size: 10; color: "black"; brand: "Reebok"; price: 59.95 }

    }

    Boy {

        name: "Jack Smith"

        shoe { size: 8; color: "blue"; brand: "Puma"; price: 19.95 }

    }

    Girl {

        name: "Anne Brown"

        BirthdayParty.rsvp: "2009-07-01"

        shoe.size: 7

        shoe.color: "red"

        shoe.brand: "Marc Jacobs"

        shoe.price: 699.99

    }

// ![1]

}

// ![1]

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>();

    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);

            QDate rsvpDate;

            QObject *attached =

                qmlAttachedPropertiesObject<BirthdayParty>(guest, false);

            if (attached)

                rsvpDate = attached->property("rsvp").toDate();

            if (rsvpDate.isNull())

                qWarning() << "   " << guest->name() << "RSVP date: Hasn't RSVP'd";

            else

                qWarning() << "   " << guest->name() << "RSVP date:" << qPrintable(rsvpDate.toString()); // 上文讨论了qPrintable的问题

        }

        party->startParty();                       // 这里调用了发射信号函数，因此party開始时间将被打印在最后一行

    } else {

        qWarning() << component.errors();

    }

    return 0;

}

结果如图：