26——Extending QML – Grouped Properties Example
最后更新于：2022-04-01 07:22:03
本系列所有文章可以在这里查看[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25——Extending QML - Methods Example](http://blog.csdn.net/cloud_castle/article/details/37391595)
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 1.0
import 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_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)
{
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("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。