Questions about signals/slots and QObject lifetimes

[themolecule]

I'm trying to find documentation about the deep nature of Signals and Slots (which are well documented in the source)...

for instance, connect() is frequently called from 'this', but if 'this' calls:

connect(that, SIGNAL(_something()), other, SLOT(_else()));

connect(that, SIGNAL(_something()), other, SLOT(_else()));

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then is the connection connected to the lifetime of 'this', or is it attached to an internal database so that deleting 'this' will allow the connection to persist?

I'm hoping that deleting 'this' will destroy the connection, but 'this' is separate from 'that' and 'other', so the question is, are connections connected to the creator or the objects?

[anda_skoa]

If you look at the signature of the connect method you used here, you will see that it is a static method of QObject.

So the "this" object is not involved at all with this connection.

The connection will persist as long as its sender and receiver exist or it is undone using QObject::disconnect().

Cheers,
_

[d_stranz]

If you look at the signature of the connect method you used here, you will see that it is a static method of QObject.

Well, yes, but the OP's question really boils down to: if one of the instances involved in the connection (either the sender or the receiver) is destroyed, is the connection also destroyed?

The answer to that is "yes". If that was not the case, things would likely be crashing all over the place due to slots being invoked with dangling, deleted pointers.

QObject has a QObject::destroyed() signal which you can use to detect when an object you are interested in has been (or is about to be) destroyed. For example, if you keep a pointer to some QObject instance in a data structure, and that QObject's lifetime was controlled by something else, you'd want to make sure that pointer was still valid before using it. If you connect to the instance's destroyed() signal, you can be notified when it goes out of scope and can take appropriate action (like set your stored pointer variable to NULL).