C++ Signal to Qml Slot in Qt

C++ signal to QML slot in Qt

I think it would be best if you check this tutorial:

http://doc.qt.io/qt-4.8/qtbinding.html

especially this section:

http://doc.qt.io/qt-4.8/qtbinding.html#receiving-signals

I think your mistake in this case might either be that you didn't declare it as a slot or you didn't make it invocable. Both options are explained in the Qt Tutorial.

Also, you need to use a QVariant in order to exchange data between C++ and QML.
You can also register types, e.g. Widgets and stuff, so that you can use them in QML as a "native" type like a rectangle. In most cases this is not recommended, except if you need some certain extern class or some data that you cannot display otherwise in your QML Interface.

The reason for the QVariant is the Script based approach of QML. The QVariant basically contains your data and a desription of the data type, so that the QML knows how to handle it properly. That's why you have to specify the parameter in QML with String, int etc.. But the original data exchange with C++ remains a QVariant

I have used the qmlRegisterType before, but it is a very inconvenient Solution for simple data types. It is rather used for more complex data, such as custom Widgets, Canvas or Video elements that QML does not natively support or extended QStandardItemModels . It is a more convenient way to exchange data between QML and C++ and does not need Signals or Slots in first instance, because the QStandardItemModel updates the GUI automatically. For using the QStandardItemModel you need to register the Type with qmlRegisterType.. . The Model can then be used in Model based Views such as the ListView etc.

I attached a tutorial for this topic, it describes how to use the QListModel.

http://doc.qt.io/qt-4.8/qdeclarativemodels.html

Connect C++ signal to QML slot

Expose your object to QML in C++:

topLevel->setContextProperty("myClass", myClass);

In QML, you can use Connections:

Connections {
    target: myClass 
    userRegistered: {
        // do something with it here
    }
}

Qt C++ Signal to Qml

You have two instances of QmlCppApi that you created. One is in main.cpp, that you call api, and the other is in QML which is the unnamed HandleQmlCppApi object. You only need one of them. To catch a signal from api you need a Connections object, like this:

Connections {
    target: api

    onTestStringSended: console.log("recieved")
}

C++ Signal is not received in QML slot

I didn't have version 5.9, but I tried it with 5.10.1. In that case, the text did not get printed to the console. I fixed it by changing the syntax on the signal handler. (Just remove function().)

    Connections {
        target: obj
        onEmitted: {
            console.log("received")
        }
    }

How can I connect a QML signal to a C++ slot within the QML file

There's a couple different ways you could do it. You could put your code in a function as @Amfasis mentioned:

Window {
    Component.onCompleted: {
        sizeChange.connect(cefWindow.resizeCEFWindow)
    }
}

Or you could just directly call your C++ slot from a signal handler, like this:

onSizeChange: {
    cefWindow.resizeCEFWindow()
}

I usually prefer the second method myself.

QT5 C++ Signal to QML Slot not working

The first letter of the property name is always capitalised in signal handlers:

onDashsetupChanged: console.log("Dashboard has changed")

Property Change Signal Handlers explains this:

A signal is automatically emitted when the value of a QML property changes. This type of signal is a property change signal and signal handlers for these signals are written in the form onChanged where is the name of the property, with the first letter capitalized.

QML signal and slot between 2 different QML

You should use a Connections object (documented here) together with the item property of the Loader:

Loader {
    id: pageLoader 
    source: "CustomObject.qml"
}

Connections {
    target: pageLoader.item

    //Qt < 5.15
    onBackPagePressed: pageLoader.source = ""

    //Qt >= 5.15
    function onBackPagePressed()
    {
        pageLoader.source = ""
    }
}

Qt c++ and Qml signal and slot connection

Specifies that type of variable the function returns
main() must return an integer

No scaling before QApplication is instantiated.

     QGuiApplication app(argc, argv);

    QFontDatabase::addApplicationFont(":/fonts/DejaVuSans.ttf");
    app.setFont(QFont("DejaVu Sans"));
// Now I am using Dialog like context property in qml
// qmlRegisterType<Dialog>("CustomExtensions",1,0,"Dialog");
Dialog dlg;
QQmlApplicationEngine engine;

// Now in qml we can access to dlg by "dialogObj" name

engine.rootContext()->setContextProperty("dialogObj", &dlg);
engine.load(QUrl(QStringLiteral("qrc:/qml/dashboard.qml")));

//QQmlApplicationEngine engine(QUrl("qrc:/qml/dashboard.qml"));       ``

Using this you can access Qt signal and slot with qml

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