How to serialize custom objects

Question

I have a problem with serializing my objects on disk. This is a simplified scenario:

I have an ObjectA that provides its own serialization operators. They work, since I can save / load data to a file. Then I have an ObjectB containing ObjectA as a data member. Trying to save an ObjectB object, I got a runtime error:

QVariant :: save: cannot save type 279.

I use this code for stream statements:

QDataStream & operator<<( QDataStream & dataStream, const ObjectA & objectA )
{
    for(int i=0; i< objectA.metaObject()->propertyCount(); ++i) {
        if(objectA.metaObject()->property(i).isStored(&objectA)) {
            dataStream << objectA.metaObject()->property(i).read(&objectA);
        }
    }
    return dataStream;
}

QDataStream & operator>>(QDataStream & dataStream, ObjectA & objectA) {
    QVariant var;
    for(int i=0; i < objectA.metaObject()->propertyCount(); ++i) {
        if(objectA.metaObject()->property(i).isStored(&objectA)) {
            dataStream >> var;
            objectA.metaObject()->property(i).write(&objectA, var);
        }
    }

    return dataStream;
}

(just replace A with B for ObjectB statements)

I think the error is in implementing ObjectB serialization, but I do not know how to do this.

Answer 1

qRegisterMetaTypeStreamOperators . :

class MyType {
  ...
};
Q_REGISTER_METATYPE(MyType);

int main(int argc, char ** argv) {
  ...
  qRegisterMetaTypeStreamOperators<MyType>();
  ...
}