QObject-derived values in container classes [modified]

giesbert

Hi,

parameter of a signal must be packable into a QVariant.
You can use your own class pointer if you declare the variant meta type for it:

@
qRegisterMetaType<Card*>("Card*");
@

With pass by value it is not usable as the base class (QObject) is not copyable and not assignable.
Pass by reference is intern also a pass by value, which means --> same behavior.

alexxx_1992

Thanks for fast answer!

I'm add
@qRegisterMetaType<Card*>("Card*");@
to Card constructor, but compiller shows me the same errrors.
Am I have to define default constructor or anything more?

andre

As Gerolf was pointing out: QObject derived classes can not be copied, and thus, not be stored in a QVariant, and thus, not be passed as arguments in a signal-slot connection.

However, you can pass pointers to QObjects. Or you can pass a smart pointer object wrapping such a pointer to a QObject.

dangelog

[quote author="Gerolf" date="1302073628"]Hi,

parameter of a signal must be packable into a QVariant.
You can use your own class pointer if you declare the variant meta type for it:

@
qRegisterMetaType<Card*>("Card*");
@
[/quote]
This is false.

In general, type registration is required only for queued connections. It's NOT necessary to do that for direct connections, no matter the datatype involved.

[quote]
With pass by value it is not usable as the base class (QObject) is not copyable and not assignable.
Pass by reference is intern also a pass by value, which means --> same behavior.[/quote]

False as well, passing by reference is simply passing by reference and it's allowed with QObjects. No copy takes place.

Apart from these considerations, the OP's problem has nothing to do with signals and slots. Please change the topic title as well. He's making what IMHO appears to be a value class (the Card class) inherit from QObject, which makes it not copiable. Therefore, @ QVector<Card> m_cards; @ is invalid, as well as things like @ m_cards.push_back (*_card); @

andre

Peppe, I think you are right. The (main) problem is in using container classes with QObject-derived value types. That won't work for the non-copyable reasons already mentioned.

alexxx_1992

I'm understand. Am I need to to do my Card class not inherit from QObject?

andre

[quote author="alexxx_1992" date="1302076299"]I'm understand. Am I need to to do my Card class not inherit from QObject?[/quote]

No. Just store pointers to the objects instead of the objects themselves in your containers. So, instead of:

@
QVector<Card> m_cards;
@

You do:

@
QVector<Card*> m_cards; // <-- note the *
@

Or, alternatively, you store smart pointers in your container. Something like:

@
QVector<QPointer<Card> > m_cards;
@

giesbert

[quote author="peppe" date="1302075488"]
[quote]
With pass by value it is not usable as the base class (QObject) is not copyable and not assignable.
Pass by reference is intern also a pass by value, which means --> same behavior.[/quote]

False as well, passing by reference is simply passing by reference and it's allowed with QObjects. No copy takes place.
[/quote]

If it's used for queued connections, it is in fact copied. So you can't genrally say it's not copied. But I was also wrong it's not always copied :-)

alexxx_1992

Thank you very much!!! It's works!!!)))
Sorry for my English)

andre

If you choose to store pointers in your container, don't forget to delete the objects in there when the container goes out of scope. That does not happen automatically. Considder adding something like this to your AbstractPokerPlayer destructor:

@
#include <QtAlgorithms>

qDeleteAll(m_cards);
m_cards.clear(); //not strictly needed
@

alexxx_1992

Thanks! I will try) I think they can't to be deleted automaticly because they are pointers and container don't have to take care about that memory. Am I rigth?

And… Could I pass into the signal QVector’s reference?

Edit: please use the edit option to add something to a posting you just made; Andre

andre

Well, the problem is, that the container will delete the contents of the container when it is deleted. Only in this case, the container contains only pointers. So it deletes the pointers, but it does not call delete on the pointers. That would be a memory leak, if there are no copies of those pointers elsewhere. I pointed out one way to fix that (do the deletion yourself at an appropriate time), but you could also use smart pointers to do it automatically.

You are allowed to pass a reference to your QVector in a signal, yes.

alexxx_1992

In this case, I will use smart pointers)
Thank you very much!