how to recognize which signal emitted in slot? - c++

Question

I connect two signals to same slot. like this:
check = new QCheckBox();
connect(check, SIGNAL(clicked()), this, SLOT(MySlot()));
connect(check, SIGNAL(toggled(bool)),this,SLOT(MySlot()));
I don't want to define an other slot. In MySlot is it possible to recognize which signal callbacks the slot?
How can I do this?

Answer 1

You might be able to use the QMetaObject/QMetaMethod data associated with the sender to get what you want (untested)...
void MyClass::MySlot ()
{
auto index = senderSignalIndex();
if (index == sender()->indexOfSignal("clicked()")) {
/*
* Got here as the result of a clicked() signal.
*/
} else if (index == sender()->indexOfSignal("toggled(bool)")) {
/*
* Got here as the result of a toggled(bool) signal.
*/
}
}
Rather than that, however, if you're using Qt5 I would suggest making use of the new signal/slot syntax along with lambdas...
check = new QCheckBox();
connect(check, &QCheckBox::clicked,
[this]()
{
MySlot(false);
});
connect(check, &QCheckBox::toggled,
[this](bool toggled)
{
MySlot(true, toggled);
});
Along with a change to the signature of MySlot...
/**
* #param from_toggled_signal If true this call was triggered by a
* QCheckBox::toggled signal, otherwise it's
* the result of a QCheckBox::clicked signal.
*
* #param toggle_value If from_toggled_signal is true then this was the
* value passed to QCheckBox::toggled, otherwise unused.
*/
void MyClass::MySlot (bool from_toggled_signal, bool toggle_value = false)
{
.
.
.
}

Answer 2

New slots can be defined on the fly using lambdas :)
class MyClass : public QWidget {
QSomeLayout m_layout{this};
QCheckBox m_check;
enum Signal { Clicked, Toggled };
Q_SLOT void mySlot(Signal);
public:
MyClass( ... ) : ... {
m_layout.addWidget(&m_check);
connect(&m_check, &QCheckBox::clicked, this, [this]{ mySlot(Clicked); });
connect(&m_check, &QCheckBox::toggled, this, [this]{ mySlot(Toggled); });
}
};

Answer 3

You can also add your own context to the signal if that helps. For instance I had a service that downloaded user avatars for multiple windows. I needed the window to only load the user it was interested in something so I would pass in the user's id as the context. Something like:
void UserService::downloadAvatar(const QString& url, const int context = 0) {
...// Make the http request, on finished:
emit onAvatarDownloaded(context, responseBody);
}