27——Extending QML – Attached Properties Example
最后更新于：2022-04-01 07:22:06
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26——Extending QML - Grouped Properties Example](http://blog.csdn.net/cloud_castle/article/details/37501567)
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
~~~
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);
}
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]
~~~
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>(); // 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;
}
~~~
显示结果如下：
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：
