I am trying to connect a QML signal to a Qt slot with following parameter types:

in QML side:

signal Sig(var info)

in Qt side:

QObject::connect(topLevel, SIGNAL(Sig(QVariantMap)), &mObj, SLOT(mSlot(QVariantMap)));

Which gives me the following:

QObject::connect: No such signal QQuickWindowQmlImpl_QML_24::Sig(QVariantMap) in ...

So, I assume that types var and QVariantMap does not match. According to this document, QVariantMap types are converted to JavaScript objects. But I am not sure if it also does the other way around.

I have implemented an opposite type of connection(Qt signal with QVariantMap, QML handler with "Connections" element) which worked just fine. I was able to get the signal's argument as a JS object.

By the way, I have also tried the same connection with string argument types in my code, so I don't think that there is another unrelated mistake in my code.

How do I pass JS objects to Qt(C ) side using signal/slot mechanism? I haven't been able to find a solution. Not even an example that matches my case(signal and slot argument types), actually. Which makes me think that I am doing some sort of design mistake.

CodePudding user response：

The parameters are QVariants on C side, so you need to do

QObject::connect(topLevel, SIGNAL(Sig(QVariant)), &mObj, SLOT(mSlot(QVariant)));

Note that you also need to change mSlot parameter type, because QVariant can't be implicitly converted to QVariantMap. To get the map in the slot, use QVariant::toMap() method, if it indeed is a map (if it isn't, this method returns empty map, and you need to do some debugging).

It works the other way around, because QVariantMap can be implicitly converted to QVariant.