Is it possible to disconnect all of a QObject'

问题:

I have a QObject A, this is connected to another QObject B. Now I want A to connect to C, a third QObject and to completely disconnect from B.

Easy peasy! Trouble is I have a lot of of A's each with their own set of signals and slots (B's/C's are more generic). So far I have been manually making a connect and a disconnect method for each different class type. The methods are basically copies of each other exchanging the connect for disconnect call, going against the don't repeat yourself).

So my question is: Is the following function possible?

void deleteAllConnections(QObject* someObject) {
    // TODO disconnect all connections owned by someObject
    // For bonus points: Is there a way of accessing the QMetaObject connected to?
}

I've poked around in the QMetaObject, QObject and the Signals and Slots documentation with no luck (though that is often not a guarantee...).

回答1:

There are at least 2 ways. First, disconnect everything.

disconnect(obj,0,0,0);
//or
obj->disconnect();

Second. Every connect() returns QMetaObject::Connection which can be copied or moved, so you can save some connections in the list and after some time, just iterate through the list and call disconnect() for every object. Example with one connection:

QMetaObject::Connection m_connection;
//…
m_connection = QObject::connect(…);
//…
QObject::disconnect(m_connection);

Bonus: no, Qt doesn't support such deep introspection, you can't get list of all connected slots or something another, but in most cases, you don't need this at all. One useful info, that Qt gives you is sender(), pointer to object that sent signal.

Edit

As doc said:

Disconnect everything connected to an object's signals

So in the next example both windows will be shown:

QWidget *a = new QWidget;
QWidget *b = new QWidget;

a->setWindowTitle("A");
b->setWindowTitle("B");

QObject::connect(a,SIGNAL(objectNameChanged(QString)),b,SLOT(show()));
QObject::connect(b,SIGNAL(objectNameChanged(QString)),a,SLOT(show()));

//a->disconnect();

a->setObjectName("A");
b->setObjectName("B");

But uncomment a->disconnect(); and only A windows will be shown. It means that QObject::connect(b,SIGNAL(objectNameChanged(QString)),a,SLOT(show())); was not disconnected as stated in the doc. If you want to solve this puzzle you can do a->disconnect(b);b->disconnect(a);, but it is of course very bad approach. So you can use second suggestion from my answer:

QList<QMetaObject::Connection> connections;

QWidget *a = new QWidget;
QWidget *b = new QWidget;

a->setWindowTitle("A");
b->setWindowTitle("B");

connections << QObject::connect(a,SIGNAL(objectNameChanged(QString)),b,SLOT(show()));
connections << QObject::connect(b,SIGNAL(objectNameChanged(QString)),a,SLOT(show()));

foreach (auto var, connections) {
    QObject::disconnect(var);
}

a->setObjectName("A");
b->setObjectName("B");