From Qt Documentation: Since slots are normal member functions, they follow the normal C++ rules when called directly. However, as slots, they can be invoked by any component, regardless of its access level, via a signal-slot connection. This means that a signal emitted from an instance of an arbitrary class can cause a private slot … Read more
If you need to reconnect signals in many places, then you could define a generic utility function like this: def reconnect(signal, newhandler=None, oldhandler=None): try: if oldhandler is not None: while True: signal.disconnect(oldhandler) else: signal.disconnect() except TypeError: pass if newhandler is not None: signal.connect(newhandler) … if connected: reconnect(myButton.clicked, function_A) else: reconnect(myButton.clicked, function_B) (NB: the loop is … Read more
According to this answer, Qt just replaces const references with copies. EDIT: Apparently not always the case… I just did a basic test program with one thread, and the reference was passed correctly. Its const-ness remained intact, as well. Anyways, yes, you do need to be wary of the variable going out of scope, plus … Read more
Update for QT5: Yes you can static void someFunction() { qDebug() << “pressed”; } // … somewhere else QObject::connect(button, &QPushButton::clicked, someFunction); In QT4 you can’t: No it is not allowed. Rather, it is allowed to use a slot which is a static function, but to be able to connect it you need an instance. In … Read more
I think Qt stores the slots a given signal is connected to, so that when you emit it all receivers are called, therefore you can access the list of receivers: For debugging purposes, you have: void QObject::dumpObjectInfo () Dumps information about signal connections, etc. for this object to the debug output. This function is useful … Read more
There are some rules that make life with signals and slots easier and cover the most common reason for defective connections. If I forgot something please tell me. 1) Check the debug console output: When execution errors occur, the debug output can show you the reason. 2) Use the full signature of signal and slot: … Read more
To understand the issue you have to understand how signals are emitted: They are simply a non-static member function call and thus require an instance to be called on (the “sender”). Typically, this instance is this (if you emit the signal from within another non-static member function of the same class), so the call syntax … Read more
First of all, you should probably not put any slots in QThreads. QThreads aren’t really meant to be derived from other than by reimplementing the run method and private methods (not signals!). A QThread is conceptually a thread controller, not a thread itself. In most cases you should deal with QObjects. Start a thread, then … Read more
First, try with boost::signal anyway. Don’t assume it will not be fast enough until you try in your specific case that is your application If it’s not efficient enough, maybe something like FastDelegate will suit your needs? (i did’nt try it but heard it was a nice solution in some cases where boost::signal don’t seem … Read more
It is possible to emit a signal from a const method by adding “const” to the signal declaration, like so: void sigLog(QString text) const; I tested this and it does compile and run, even though you don’t actually implement the signal as a normal method yourself (i.e. Qt is okay with it).