16.1.1. Abstract Factory

16.1.1. Abstract Factory
	16.1. Creational Patterns

[ fromfile: factory.xml id: abstractfactory ]

AbstractFactory, defined in Example 16.1, is a simple class:

Example 16.1. src/libs/dataobjects/abstractfactory.h

[ . . . . ]
class DOBJS_EXPORT AbstractFactory 
{
  public:
    virtual QObject* newObject (QString className, 
                                QObject* parent=0) = 0;
    virtual ~AbstractFactory();
	
};
[ . . . . ]

The newObject() method is pure virtual, so it must be overridden in derived classes.

Example 16.2. src/libs/dataobjects/objectfactory.h

[ . . . . ]
class DOBJS_EXPORT  ObjectFactory : public AbstractFactory {
  public:
    ObjectFactory();
    virtual QObject* newObject (QString className, QObject* parent=0);
 protected:
    QHash<QString, QMetaObject> m_knownClasses;
};
[ . . . . ]

We have defined ObjectFactory so that it knows how to create two concrete types.
For unknown types, it returns a pointer to a generic QObject with only the dynamic className property set.

Example 16.3. src/libs/dataobjects/objectfactory.cpp

[ . . . . ]

ObjectFactory::ObjectFactory() {
    m_knownClasses["UsAddress"] = UsAddress::staticMetaObject;
    m_knownClasses["CanadaAddress"] = CanadaAddress::staticMetaObject;
}

QObject* ObjectFactory::newObject(QString className, QObject* parent) {
    QObject* retval = 0;
    if (m_knownClasses.contains(className)) {
        const QMetaObject& mo = m_knownClasses[className];
        retval = mo.newInstance();      
        if (retval == 0) {
            qDebug() << "Error creating " << className;
            abort();
        }
    } else {
        qDebug() << QString("Generic QObject created for new %1")
                    .arg(className);
        retval = new QObject();
        retval->setProperty("className", className);
    }
    if (parent != 0) retval->setParent(parent);
    return retval;
}

Requires Qt 4.5 or later.

Example 16.4 shows an example use of the Q_INVOKABLE macro with the constructor for the UsAddress class.

Example 16.4. src/libs/dataobjects/address.h

[ . . . . ]

class DOBJS_EXPORT UsAddress : public Address {
    Q_OBJECT
  public:
    Q_PROPERTY( QString State READ getState WRITE setState );
    Q_PROPERTY( QString Zip READ getZip WRITE setZip );
    explicit Q_INVOKABLE UsAddress(QString name=QString(), QObject* parent=0) 
                                  : Address(name, parent) {}
  protected:
    static QString getPhoneFormat();
  public:
[ . . . . ]

  private:
    QString m_State, m_Zip;
};


16.1. Creational Patterns		16.1.2. Abstract Factories and Libraries