本系列全部文章能够在这里查看http://blog.csdn.net/cloud_castle/article/category/2123873

接上文Qt5官方demo解析集29——Extending
QML - Property Value Source Example

还记得我们以前在Qt5官方demo解析集17——Chapter
3: Adding Property Bindings一文中接触过QML自己定义类型的属性绑定吗？假设不记得了，能够移步进行了解。由于项目尺寸的原因，那个样例可能更好理解。

这个样例也是我们Extending QML(扩展QML)系列的最后一个样例了，尽管相较前一个样例也仅仅有小小的修改。只是我们还是把整个project都完整的看一遍吧~

binding.qrc中是我们的qml文件，它实例化了BirthdayParty类以及其全部的子对象。

Person类建立了一个自己定义的QML类型，因为它并非一个可视化组件，且QML不论什么组件均基于Qt 的元对象系统，因此继承自QObject。

接着定义了ShoeDescription用来对Person类的shoe属性进行描写叙述，使用特定的方法。我们在对shoe赋值时不须要实例化这个ShoeDescription组件。

再定义两个Person的派生类Boy、Girl，能够用来对Person对象分类。

person.h:

#ifndef PERSON_H

#define PERSON_H

#include <QObject>

#include <QColor>

class ShoeDescription : public QObject

{

    Q_OBJECT

    Q_PROPERTY(int size READ size WRITE setSize NOTIFY shoeChanged)        // NOTIFY用在属性绑定，当该属性值发生改变时发出信号shoeChanged

    Q_PROPERTY(QColor color READ color WRITE setColor NOTIFY shoeChanged)  // 通过该信号，我们就能使得被绑定的属性值随之发生改变

    Q_PROPERTY(QString brand READ brand WRITE setBrand NOTIFY shoeChanged)

    Q_PROPERTY(qreal price READ price WRITE setPrice NOTIFY shoeChanged)

public:

    ShoeDescription(QObject *parent = 0);

    int size() const;

    void setSize(int);

    QColor color() const;

    void setColor(const QColor &);

    QString brand() const;

    void setBrand(const QString &);

    qreal price() const;

    void setPrice(qreal);

signals:

    void shoeChanged();                      // 定义该shoeChanged()信号

private:

    int m_size;

    QColor m_color;

    QString m_brand;

    qreal m_price;

};

class Person : public QObject

{

    Q_OBJECT

    Q_PROPERTY(QString name READ name WRITE setName NOTIFY nameChanged)

// ![0]

    Q_PROPERTY(ShoeDescription *shoe READ shoe CONSTANT)

// ![0]

public:

    Person(QObject *parent = 0);

    QString name() const;

    void setName(const QString &);

    ShoeDescription *shoe();

signals:

    void nameChanged();

private:

    QString m_name;

    ShoeDescription m_shoe;

};

class Boy : public Person

{

    Q_OBJECT

public:

    Boy(QObject * parent = 0);

};

class Girl : public Person

{

    Q_OBJECT

public:

    Girl(QObject * parent = 0);

};

#endif // PERSON_H

person.cpp:

#include "person.h"

ShoeDescription::ShoeDescription(QObject *parent)

: QObject(parent), m_size(0), m_price(0)

{

}

int ShoeDescription::size() const

{

    return m_size;

}

void ShoeDescription::setSize(int s)

{

    if (m_size == s)

        return;

    m_size = s;

    emit shoeChanged();                   // 该信号应该在该属性被正确写入后发出

}

QColor ShoeDescription::color() const

{

    return m_color;

}

void ShoeDescription::setColor(const QColor &c)

{

    if (m_color == c)

        return;

    m_color = c;

    emit shoeChanged();

}

QString ShoeDescription::brand() const

{

    return m_brand;

}

void ShoeDescription::setBrand(const QString &b)

{

    if (m_brand == b)

        return;

    m_brand = b;

    emit shoeChanged();

}

qreal ShoeDescription::price() const

{

    return m_price;

}

void ShoeDescription::setPrice(qreal p)

{

    if (m_price == p)

        return;

    m_price = p;

    emit shoeChanged();

}

Person::Person(QObject *parent)

: QObject(parent)

{

}

QString Person::name() const

{

    return m_name;

}

void Person::setName(const QString &n)

{

    if (m_name == n)

        return;

    m_name = n;

    emit nameChanged();

}

ShoeDescription *Person::shoe()

{

    return &m_shoe;

}

Boy::Boy(QObject * parent)

: Person(parent)

{

}

Girl::Girl(QObject * parent)

: Person(parent)

{

}

接下来是我们的主类BirthdayParty，它也是example.qml中的根项目。它有一个以Person指针为參数的host属性，用来指明寿星；有一个以Person列表指针为參数guests属性，用来指明客人，而且该属性被设置为默认属性，这样在QML中没有指明属性的值将被划归它的名下。一个announcement属性，用来被动态改变以播放歌词。另外，该类还定义了一个partyStarted()信号，我们能够在QML中使用onPartyStarted
来响应该信号。

此外，再定义一个BirthdayPartyAttached类。它用来为BirthdayParty提供一个附加属性。

birthdayparty.h:

#ifndef BIRTHDAYPARTY_H

#define BIRTHDAYPARTY_H

#include <QObject>

#include <QDate>

#include <QDebug>

#include <qqml.h>

#include "person.h"

class BirthdayPartyAttached : public QObject

{

    Q_OBJECT

    Q_PROPERTY(QDate rsvp READ rsvp WRITE setRsvp NOTIFY rsvpChanged)  // 该例中大多数属性均定义了属性绑定

public:

    BirthdayPartyAttached(QObject *object);

    QDate rsvp() const;

    void setRsvp(const QDate &);

signals:

    void rsvpChanged();

private:

    QDate m_rsvp;

};

class BirthdayParty : public QObject

{

    Q_OBJECT

// ![0]

    Q_PROPERTY(Person *host READ host WRITE setHost NOTIFY hostChanged)

// ![0]

    Q_PROPERTY(QQmlListProperty<Person> guests READ guests)

    Q_PROPERTY(QString announcement READ announcement WRITE setAnnouncement)

    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;

    QString announcement() const;

    void setAnnouncement(const QString &);

    static BirthdayPartyAttached *qmlAttachedProperties(QObject *);

    void startParty();

signals:

    void partyStarted(const QTime &time);

    void hostChanged();

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)

{

    if (d != m_rsvp) {

        m_rsvp = d;

        emit rsvpChanged();

    }

}

BirthdayParty::BirthdayParty(QObject *parent)

: QObject(parent), m_host(0)

{

}

Person *BirthdayParty::host() const

{

    return m_host;

}

void BirthdayParty::setHost(Person *c)

{

    if (c == m_host) return;

    m_host = c;

    emit hostChanged();

}

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()

{

    QTime time = QTime::currentTime();

    emit partyStarted(time);

}

QString BirthdayParty::announcement() const

{

    return QString();

}

void BirthdayParty::setAnnouncement(const QString &speak)

{

    qWarning() << qPrintable(speak);

}

BirthdayPartyAttached *BirthdayParty::qmlAttachedProperties(QObject *object)

{

    return new BirthdayPartyAttached(object);

}

在该系列第9个样例中，我们接触到了HappyBirthdaySong类，它是一个自己定义的Property Value Source，用来为QML属性提供随时间变化的能力，类似于Animation。在该样例中，它被用于announcement属性。

happybirthdaysong.h:

#ifndef HAPPYBIRTHDAYSONG_H

#define HAPPYBIRTHDAYSONG_H

#include <QQmlPropertyValueSource>

#include <QQmlProperty>

#include <QStringList>

class HappyBirthdaySong : public QObject, public QQmlPropertyValueSource

{

    Q_OBJECT

    Q_PROPERTY(QString name READ name WRITE setName NOTIFY nameChanged)

    Q_INTERFACES(QQmlPropertyValueSource)

public:

    HappyBirthdaySong(QObject *parent = 0);

    virtual void setTarget(const QQmlProperty &);

    QString name() const;

    void setName(const QString &);

private slots:

    void advance();

signals:

    void nameChanged();

private:

    int m_line;

    QStringList m_lyrics;

    QQmlProperty m_target;

    QString m_name;

};

#endif // HAPPYBIRTHDAYSONG_H

happybirthdaysong.cpp:

#include "happybirthdaysong.h"

#include <QTimer>

HappyBirthdaySong::HappyBirthdaySong(QObject *parent)

: QObject(parent), m_line(-1)

{

    setName(QString());

    QTimer *timer = new QTimer(this);

    QObject::connect(timer, SIGNAL(timeout()), this, SLOT(advance()));

    timer->start(1000);

}

void HappyBirthdaySong::setTarget(const QQmlProperty &p)

{

    m_target = p;

}

QString HappyBirthdaySong::name() const

{

    return m_name;

}

void HappyBirthdaySong::setName(const QString &name)

{

    if (m_name == name)

        return;

    m_name = name;

    m_lyrics.clear();

    m_lyrics << "Happy birthday to you,";

    m_lyrics << "Happy birthday to you,";

    m_lyrics << "Happy birthday dear " + m_name + ",";

    m_lyrics << "Happy birthday to you!";

    m_lyrics << "";

    emit nameChanged();

}

void HappyBirthdaySong::advance()

{

    m_line = (m_line + 1) % m_lyrics.count();

    m_target.write(m_lyrics.at(m_line));

}

在main.cpp中将这些C++类注冊成QML类型后。我们就能够在QML中创建一个实例化的BirthdayParty，并对其属性赋值:

example.qml:

import People 1.0

import QtQuick 2.0  // For QColor

// ![0]

BirthdayParty {

    id: theParty

    HappyBirthdaySong on announcement { name: theParty.host.name }      // 属性绑定

    host: Boy {

        name: "Bob Jones"

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

    }

// ![0]

    onPartyStarted: console.log("This party started rockin' at " + time);

    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]

最后，在main.cpp调用这个属性的信息。并基于一定的规则输出这些信息：

#include <QCoreApplication>

#include <QQmlEngine>

#include <QQmlComponent>

#include <QDebug>

#include "birthdayparty.h"

#include "happybirthdaysong.h"

#include "person.h"

int main(int argc, char ** argv)

{

    QCoreApplication app(argc, argv);

    qmlRegisterType<BirthdayPartyAttached>();

    qmlRegisterType<BirthdayParty>("People", 1,0, "BirthdayParty");

    qmlRegisterType<HappyBirthdaySong>("People", 1,0, "HappyBirthdaySong");

    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());

        }

        party->startParty();

    } else {

        qWarning() << component.errors();

    }

    return app.exec();

}

输出例如以下：

watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvY2xvdWRfY2FzdGxl/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast" alt="">

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