Help with Q_PROPERTY with object pointer

[lni]

Hello,

I am trying to have a generic save/restore for QObject which contain QObject derived pointer, as shown in the example, the "Parent" has "Object", but I can't use
Q_PROPERTY( QObject *object READ object WRITE setObject )

I would like to use
Q_PROPERTY( Object *object READ object WRITE setObject )

In this way, I don't need to cast from QObject to Object. Is there a way for that? Thanks!

#include <QObject>
#include <QString>
#include <QFile>
#include <QDebug>
#include <QMap>
#include <QDataStream>
#include <QMetaObject>
#include <QByteArray>
#include <QVariant>
#include <QMetaProperty>
#include <QList>
#include <QMetaType>
#include <QBuffer>
#include <iostream>
 
class Object : public QObject
{
  Q_OBJECT
  Q_PROPERTY(QString string READ string WRITE setString)
 
public:
 
  Object() {
  }
 
  const QString& string() const {
    return str;
  }
 
  void setString(const QString &ss) {
    str = ss;
  }
 
  void dump() const {
    std::cout << str.toStdString() << std::endl;
  }
 
private:
 
  QString str;
 
};
 
 
class Parent : public QObject
{
  Q_OBJECT
  Q_PROPERTY(QObject *object READ object WRITE setObject)
 
public:
 
  Parent() {
  }
 
  QObject * object() const {
    return obj;
  }
 
  void setObject(QObject * oo) {
    Q_ASSERT(!oo || qobject_cast<Object*>(oo));
    obj = qobject_cast<Object*>(oo);
  }
 
private:
 
  Object                *obj;
 
};
 
class BaseInterface
{
public:
 
  virtual ~BaseInterface() {}
  virtual QObject *create( const QString &objectName) const = 0;
 
};
 
template <typename T>
class Creator : public BaseInterface
{
public:
 
  QObject *create( const QString &objectName) const {
    T *ret = new T;
    ret->setObjectName(objectName);
    return ret;
  }
};
 
class Factory
{
public:
 
  static QObject *create(const QString &className, const QString &objectName) {
    BaseInterface *i = interfaces.value(className, 0);
    assert (i);
    return i->create(objectName);
  }
 
  static void registerClass(const QString &className, BaseInterface *interface) {
    if (!interface) {
      delete interfaces.value(className, 0);
      interfaces.remove(className);
    } else {
      interfaces[className] = interface;
    }
  }
 
  static QMap<QString, BaseInterface*> interfaces;
 
};
 
QMap<QString, BaseInterface*> Factory::interfaces;
 
static void save(QObject *o, QIODevice *dev)
{
  const QMetaObject *mo = o->metaObject();
  QMap<QByteArray, QVariant> properties;
  QMap<QByteArray, QByteArray> objectStarProperties;
  QMap<QByteArray, QVariantList> listProp;;
 
  const int props = mo->propertyCount();
  for (int i=0; i<props; ++i) {
    const QMetaProperty prop = mo->property(i);
    if (prop.userType() == QMetaType::QObjectStar) {
      QObject *obj = qVariantValue<QObject*>(prop.read(o));
      if (obj) {
        QBuffer buf;
        buf.open(QIODevice::WriteOnly);
        save(obj, &buf);
        objectStarProperties[prop.name()] = buf.buffer();
      }
    } else if (prop.userType() == QMetaType::QVariantList) {
      listProp[prop.name()] = prop.read(o).toList();
    } else {
      properties[prop.name()] = prop.read(o);
    }
  }
 
  QDataStream ds(dev);
  ds << QString::fromLatin1(mo->className());
  ds << properties;
  ds << objectStarProperties;
 
  ds << listProp.size();
  QMapIterator<QByteArray, QVariantList> it1( listProp );
  while( it1.hasNext() ) {
    it1.next();
    QVariantList vlist = it1.value();
    ds << vlist.size() << it1.key();
  }
 
}
static QObject *read(QIODevice *dev, QObject *parent = 0)
{
  QString className;
  QMap<QByteArray, QVariant> properties;
  QMap<QByteArray, QByteArray> objectStarProperties;
 
  QDataStream ds(dev);
 
  ds >> className;
  ds >> properties;
  ds >> objectStarProperties;
 
  int nlists;
  ds >> nlists;
 
  QList<int> iList;
  QList<QByteArray> propNameList;
  for ( int idx=0; idx<nlists; idx++ ) {
    int il;
    QByteArray pnl;
    ds >> il >> pnl;
    iList.append( il );
    propNameList.append( pnl );
  }
 
  QObject *o = Factory::create(className,
                               properties.value("objectName").toString());
  if (!o) {
    qWarning() << "Can't create object of type" << className;
    return 0;
  }
 
  for (QMap<QByteArray, QVariant>::const_iterator it = properties.begin();
       it != properties.end(); ++it) {
    if (!o->setProperty(it.key().constData(), it.value())) {
      qWarning() << "Can't set" << it.key();
    }
  }
 
  for (QMap<QByteArray, QByteArray>::const_iterator it =
         objectStarProperties.begin();
       it != objectStarProperties.end(); ++it) {
    QBuffer buf;
    buf.setData(it.value());
    buf.open(QIODevice::ReadOnly);
    QObject *obj = read(&buf, 0);
    o->setProperty(it.key(), qVariantFromValue<QObject*>(obj));
  }
 
  for ( int idx=0; idx<nlists; idx++ ) {
    QVariantList objList;
    for (int ii=0; ii<iList[idx]; ++ii) {
      QObject* oo = read(dev, o);
      objList << qVariantFromValue<QObject*>( oo );
    }
    o->setProperty( propNameList[idx], objList );
  }
 
  return o;
 
}
 
#include "main.moc"
 
int main()
{
  Factory::registerClass("Parent", new Creator<Parent>());
  Factory::registerClass("Object", new Creator<Object>());
 
  Object *o = new Object;
  o->setString("foobar");
 
  Parent *p = new Parent;
  p->setObject(o);
 
  qobject_cast<Object*>( p->object() )->dump();
 
  QFile file("tt.ss");
  file.open(QIODevice::WriteOnly);
 
  save(p, &file);
  file.close();
 
  file.open(QIODevice::ReadOnly);
 
  QObject *root = read(&file);
  Q_ASSERT(root);
  Parent *pp = qobject_cast<Parent*>(root);
 
  qobject_cast<Object*>( pp->object() )->dump();
 
  return 0;
}

#include <QObject>
#include <QString>
#include <QFile>
#include <QDebug>
#include <QMap>
#include <QDataStream>
#include <QMetaObject>
#include <QByteArray>
#include <QVariant>
#include <QMetaProperty>
#include <QList>
#include <QMetaType>
#include <QBuffer>
#include <iostream>

class Object : public QObject
{
  Q_OBJECT
  Q_PROPERTY(QString string READ string WRITE setString)

public:

  Object() {
  }

  const QString& string() const {
    return str;
  }

  void setString(const QString &ss) {
    str = ss;
  }

  void dump() const {
    std::cout << str.toStdString() << std::endl;
  }

private:

  QString str;

};


class Parent : public QObject
{
  Q_OBJECT
  Q_PROPERTY(QObject *object READ object WRITE setObject)

public:

  Parent() {
  }

  QObject * object() const {
    return obj;
  }

  void setObject(QObject * oo) {
    Q_ASSERT(!oo || qobject_cast<Object*>(oo));
    obj = qobject_cast<Object*>(oo);
  }

private:

  Object                *obj;

};

class BaseInterface
{
public:

  virtual ~BaseInterface() {}
  virtual QObject *create( const QString &objectName) const = 0;

};

template <typename T>
class Creator : public BaseInterface
{
public:

  QObject *create( const QString &objectName) const {
    T *ret = new T;
    ret->setObjectName(objectName);
    return ret;
  }
};

class Factory
{
public:

  static QObject *create(const QString &className, const QString &objectName) {
    BaseInterface *i = interfaces.value(className, 0);
    assert (i);
    return i->create(objectName);
  }

  static void registerClass(const QString &className, BaseInterface *interface) {
    if (!interface) {
      delete interfaces.value(className, 0);
      interfaces.remove(className);
    } else {
      interfaces[className] = interface;
    }
  }

  static QMap<QString, BaseInterface*> interfaces;

};

QMap<QString, BaseInterface*> Factory::interfaces;

static void save(QObject *o, QIODevice *dev)
{
  const QMetaObject *mo = o->metaObject();
  QMap<QByteArray, QVariant> properties;
  QMap<QByteArray, QByteArray> objectStarProperties;
  QMap<QByteArray, QVariantList> listProp;;

  const int props = mo->propertyCount();
  for (int i=0; i<props; ++i) {
    const QMetaProperty prop = mo->property(i);
    if (prop.userType() == QMetaType::QObjectStar) {
      QObject *obj = qVariantValue<QObject*>(prop.read(o));
      if (obj) {
        QBuffer buf;
        buf.open(QIODevice::WriteOnly);
        save(obj, &buf);
        objectStarProperties[prop.name()] = buf.buffer();
      }
    } else if (prop.userType() == QMetaType::QVariantList) {
      listProp[prop.name()] = prop.read(o).toList();
    } else {
      properties[prop.name()] = prop.read(o);
    }
  }

  QDataStream ds(dev);
  ds << QString::fromLatin1(mo->className());
  ds << properties;
  ds << objectStarProperties;

  ds << listProp.size();
  QMapIterator<QByteArray, QVariantList> it1( listProp );
  while( it1.hasNext() ) {
    it1.next();
    QVariantList vlist = it1.value();
    ds << vlist.size() << it1.key();
  }

}
static QObject *read(QIODevice *dev, QObject *parent = 0)
{
  QString className;
  QMap<QByteArray, QVariant> properties;
  QMap<QByteArray, QByteArray> objectStarProperties;

  QDataStream ds(dev);

  ds >> className;
  ds >> properties;
  ds >> objectStarProperties;

  int nlists;
  ds >> nlists;

  QList<int> iList;
  QList<QByteArray> propNameList;
  for ( int idx=0; idx<nlists; idx++ ) {
    int il;
    QByteArray pnl;
    ds >> il >> pnl;
    iList.append( il );
    propNameList.append( pnl );
  }

  QObject *o = Factory::create(className,
                               properties.value("objectName").toString());
  if (!o) {
    qWarning() << "Can't create object of type" << className;
    return 0;
  }

  for (QMap<QByteArray, QVariant>::const_iterator it = properties.begin();
       it != properties.end(); ++it) {
    if (!o->setProperty(it.key().constData(), it.value())) {
      qWarning() << "Can't set" << it.key();
    }
  }

  for (QMap<QByteArray, QByteArray>::const_iterator it =
         objectStarProperties.begin();
       it != objectStarProperties.end(); ++it) {
    QBuffer buf;
    buf.setData(it.value());
    buf.open(QIODevice::ReadOnly);
    QObject *obj = read(&buf, 0);
    o->setProperty(it.key(), qVariantFromValue<QObject*>(obj));
  }

  for ( int idx=0; idx<nlists; idx++ ) {
    QVariantList objList;
    for (int ii=0; ii<iList[idx]; ++ii) {
      QObject* oo = read(dev, o);
      objList << qVariantFromValue<QObject*>( oo );
    }
    o->setProperty( propNameList[idx], objList );
  }

  return o;

}

#include "main.moc"

int main()
{
  Factory::registerClass("Parent", new Creator<Parent>());
  Factory::registerClass("Object", new Creator<Object>());

  Object *o = new Object;
  o->setString("foobar");

  Parent *p = new Parent;
  p->setObject(o);

  qobject_cast<Object*>( p->object() )->dump();

  QFile file("tt.ss");
  file.open(QIODevice::WriteOnly);

  save(p, &file);
  file.close();

  file.open(QIODevice::ReadOnly);

  QObject *root = read(&file);
  Q_ASSERT(root);
  Parent *pp = qobject_cast<Parent*>(root);

  qobject_cast<Object*>( pp->object() )->dump();

  return 0;
}

To copy to clipboard, switch view to plain text mode 

[jpn]

Properties tend to be value types. Does it make sense to serialize a pointer value to a file?