Specify Qt::QueuedConnection for connections made via the Connections QML type

[vikramg]

I have an application where signals are sent between QML and a worker running in a separate QThread. When connections are made in C++ via QObject::connect, everything works as expected. I have not specified a ConnectionType; presumably the default of AutoConnection does the right thing and uses QueuedConnection since the receiver is in a different thread.

My code could get cleaned up vastly if I could just connect via the Connections QML type as demonstrated here: https://www.wisol.ch/w/articles/2014-12-15-qt-signal-slots-qml-cpp/. I had hoped that such connections would also default to using AutoConnection, but it appears that that is not so. I'm seeing warnings like QObject::killTimer: Timers cannot be stopped from another thread which suggest that a DirectConnection is being made.

Is there any way to specify QueuedConnection in a Connections object?

[J.Hilk]

@vikramg
yes of course, the connection typ is always the 5th parameter. Most of the time you don't write it down, as it has a preset of Qt::AutoConnection

connect(qmlObj, SIGNAL(someSignal(QVariant)), cppObj, SLOT(someSlot(QVariant)),Qt::QueuedConnection );

should work just fine,

[vikramg]

@J.Hilk
No, I'm talking specifically about not using the QObject::connect method; instead using a Connections object in QML, as shown in the link in my original post:

Window {
  Connections {
    target: receiver
    onSendToQml: {
    console.log("Received in QML from C++: " + count)
    }
  }
  MouseArea {
    anchors.fill: parent
    onClicked: {
      receiver.receiveFromQml(42);
    }
  }
}

In this case, no explicit connect calls are needed; they get arranged for you via the Connections object instantiation in QML. receiveFromQml() automatically invokes a slot from QML to C++ and the sendToQml() member function of the Receiver class automatically results in an onSendToQml() signal in QML.

In this kind of implicit signal/slot connection, is there a way to specify QueuedConnection?

[J.Hilk]

@vikramg oh, you want to go that route.
AFAIK theres no such thing. But you could connect your slot to a singleshot timer that basically emulates a QueuedConnection:

Connections {
    target: receiver
    onSendToQml: { QueuedTimer.start()}
  }

Timer {
    id: QueuedTimer
    interval: 1
    onTriggered:{     console.log("Received in QML from C++: " + count) }
}

But mabe someone else knows more about this topic.

[vikramg]

Thanks @J.Hilk
Yes, the C++ connect calls work fine; I did want to try with a Connections object in QML because that would clean up many connect calls in C++.