Call an async slot without connecting to it using a clear line of code
I ran into a rather bizarre error - QAction::trigger
a blocking dialog popped up, causing my server that called to trigger
be stuck (for example, unable to process socket signals until the dialog was closed).
I figured out a workaround. I connect the signal void triggerWorkaround()
to the slot QAction::trigger
with Qt::QueuedConnection
and I emit it:
QObject::connect(this, &HackClass::triggerWorkaround, targetAction_.data(), &QAction::trigger, Qt::QueuedConnection);
emit triggerWorkaround();
QObject::disconnect(this, nullptr, targetAction_.data(), nullptr);
But these are three lines of confusing code. Is there some weird way to do this? I found QMetaObject::invokeMethod
, but frankly 10 times more confusing than my current solution. Also, I don't want to use the method name as a string!
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You can split it into a function QueuedInvoke
like this:
//overload for methods/slots
//the slot gets invoked in the thread where the QObject lives
template <typename Object, typename T>
void QueuedInvoke(Object* object, T (Object::* f)()){
QObject signalSource;
QObject::connect(&signalSource, &QObject::destroyed,
object, f, Qt::QueuedConnection);
}
//overload for functors
//the functor gets invoked in the thread where the contextObject lives
//or in the current thread if no contextObject is provided
template <typename Func>
void QueuedInvoke(Func&& f, QObject* contextObject = QAbstractEventDispatcher::instance()){
QObject signalSource;
QObject::connect(&signalSource, &QObject::destroyed,
contextObject, std::forward<Func>(f), Qt::QueuedConnection);
}
This will use the signal destroyed()
emitted from the temp QObject
to place the queue event in the event loop. The slot / functor is actually called when the event loop handles that event.
So, instead of the three lines printed out, you can use the above function like this:
QueuedInvoke(targetAction_.data(), &QAction::trigger);
My answer is based on this excellent answer about executing a functor in a given one QThread
. You can contact him for more information.
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