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

本系列所有文章可以在这里查看http://blog.csdn.net/cloud_castle/article/category/2123873

接上文Qt5官方demo解析集25——Extending QML - Methods Example

如果之前看过了我前面介绍粒子系统的朋友，应该对

velocity: AngleDirection {angleVariation: 360; magnitude: 80; magnitudeVariation: 40}  

这样的属性设置格式屡见不鲜了，它实际是将一个AngleDirection类型作为velocity的属性值，这样我们就可以通过设置AngleDirection的属性值来达到对velocity更复杂的控制。

在这个例子中，Qt 向我们展示了一种更巧妙的做法 —— 直接使用AngleDirection的属性。

可能你之前经常会使用到font.family: "Ubuntu" 或是 font.pixelSize: 24 ，实际上这里的font 也是一个集合属性。

还是先把我们的项目文件介绍一下：

两个自定义的C++类：Person与BirthdayParty，资源文件中是我们的QML文件example.qml。

为了有一个直观的印象，我们先来看看qml的实现：
example.qml:

import People 1.0import QtQuick 2.0  // For QColor// ![0]BirthdayParty {    host: Boy {        name: "Bob Jones"        shoe { size: 12; color: "white"; brand: "Bikey"; price: 90.0 }   // QML语法基础保证冒号为一个赋值运算    }                                                                    // 而这个语句保证了属性赋值在大括号内部进行    Boy {        name: "Leo Hodges"//![grouped]        shoe { size: 10; color: "black"; brand: "Thebok"; price: 59.95 }//![grouped]    }    // ![1]    Boy {        name: "Jack Smith"        shoe {            size: 8            color: "blue"            brand: "Luma"            price: 19.95        }    }    // ![1]    Girl {        name: "Anne Brown"//![ungrouped]        shoe.size: 7                                 // 大括号拆开来实际就变成这几个单独的语句        shoe.color: "red"        shoe.brand: "Job Macobs"        shoe.price: 699.99//![ungrouped]    }}// ![0]

这种赋值方法是如何实现的呢，来看C++的定义：

BirthdayParty提供了生日派对的框架，这个类没有变化。birthdayparty.h:

#ifndef BIRTHDAYPARTY_H#define BIRTHDAYPARTY_H#include <QObject>#include <QQmlListProperty>#include "person.h"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;private:    Person *m_host;    QList<Person *> m_guests;};

birthdayparty.cpp:

#include "birthdayparty.h"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);}

接下来，Person文件中定义了一个额外的类ShoeDescription用来为shoe属性提供描述。

person.h:

#ifndef PERSON_H#define PERSON_H#include <QObject>#include <QColor>class ShoeDescription : public QObject            // 这个类的作用类似我们前面所说的AngleDirection，用这个自定义类型定义shoe属性{    Q_OBJECT    Q_PROPERTY(int size READ size WRITE setSize)        // 内部定义了四种属性：尺寸、颜色、品牌、价格    Q_PROPERTY(QColor color READ color WRITE setColor)    Q_PROPERTY(QString brand READ brand WRITE setBrand)    Q_PROPERTY(qreal price READ price WRITE setPrice)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);private:    int m_size;    QColor m_color;    QString m_brand;    qreal m_price;};class Person : public QObject                       // Person类定义{    Q_OBJECT    Q_PROPERTY(QString name READ name WRITE setName)// ![1]    Q_PROPERTY(ShoeDescription *shoe READ shoe)     // 将shoe属性设置为只读，否则它需要被冒号赋值// ![1]public:    Person(QObject *parent = 0);    QString name() const;    void setName(const QString &);    ShoeDescription *shoe();private:    QString m_name;    ShoeDescription m_shoe;};class Boy : public Person{    Q_OBJECTpublic:    Boy(QObject * parent = 0);};class Girl : public Person{    Q_OBJECTpublic:    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){    m_size = s;}QColor ShoeDescription::color() const{    return m_color;}void ShoeDescription::setColor(const QColor &c){    m_color = c;}QString ShoeDescription::brand() const{    return m_brand;}void ShoeDescription::setBrand(const QString &b){    m_brand = b;}qreal ShoeDescription::price() const{    return m_price;}void ShoeDescription::setPrice(qreal p){    m_price = p;}Person::Person(QObject *parent): QObject(parent){}QString Person::name() const{    return m_name;}void Person::setName(const QString &n){    m_name = n;}ShoeDescription *Person::shoe(){    return &m_shoe;}Boy::Boy(QObject * parent): Person(parent){}Girl::Girl(QObject * parent): Person(parent){}

最后来看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<BirthdayParty>("People", 1,0, "BirthdayParty");    qmlRegisterType<ShoeDescription>();                          // 注册该类型，但不进行实例化，这与Person类相同    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:";        Person *bestShoe = 0;        for (int ii = 0; ii < party->guestCount(); ++ii) {       // 比较每个客人鞋子价格，得出谁穿着最好的鞋            Person *guest = party->guest(ii);            qWarning() << "   " << guest->name();            if (!bestShoe || bestShoe->shoe()->price() < guest->shoe()->price())                bestShoe = guest;        }        if (bestShoe)            qWarning() << bestShoe->name() << "is wearing the best shoes!";    } else {        qWarning() << component.errors();    }    return 0;}

运行效果：

可以看到，要想实现类似

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

这种“群属性”的设置方法，我们只需要设置shoe为只读就可以了，这样QML编译器就不会寻找shoe后面的冒号，进入大括号后的赋值语句，实际上是对ShoeDescription属性的赋值。

那么如果我们想要实现这种写法

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

该如何改动呢？

第一点是shoe属性的声明，它必须是可读写的：

Q_PROPERTY(ShoeDescription *shoe READ shoe WRITE setShoe) 

当然还有对应的setShoe()函数的实现。

第二点是在main.cpp中QML类型的注册：

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

这里的ShoeDescription就需要被实例化了。

这样就可以再次运行了。