Couldn't catch signal from Cpp in QML

johndummy

I'm trying to transfer some QString from cpp to qml. Here are the steps I've done so far.

Created a class inherited from QObject and defined signal in it.

class exampleClass: public QObject {

    Q_OBJECT
.
.
signals:

void mySignal (QString myStr);

}

Somewhere in the class implementation, i emit the signal i.e.

void exampleClass::exampleFtn( . . . ){
.
.
qDebug("Before transmitting Signal");        // This gets triggered
emit mySignal ("Hello from CPP");

}

In my main.cpp, I've initialized the class and expose it to QML i.e.

int main(...) {

.
.
exampleClass *exampleObj= new exampleClass(&app);
Engine.rootContext()->setContextProperty("exampleObj",  exampleObj);
}

And finally, in QML i have connected the signal i.e.

Window {

.
.
Connections {
        target: exampleObj
        function mySignal(myStr) {
            console.log("signal from C++ recieved !")    // Doesn't get triggered
            console.log(myStr)                                           //  Doesn't get triggered
        }
    }

sierdzio

@johndummy you've got it almost correct. The only error I see is that in QML, inside of Connections, you should make the function name match your signal. So:

Connections {
        target: exampleObj
        function mySignal(myStr) {
            console.log("signal from C++ recieved !")    // Doesn't get triggered
            console.log(myStr)                                           //  Doesn't get triggered
        }
    }

johndummy

@sierdzio : That's a typo error in the post. sorry for that.

My function name match exactly with my signal. The qml doesn't give me runtime error or warnings. I still don't get why i'm not able to capture the signal.

P.S: I will edit my initial post to correct the typo (if you don't mind).

johndummy

I changed mySignal to onMySignal and it worked now.

    function onMySignal(myStr) {
        console.log("signal from C++ recieved !")  
        console.log(myStr)                                           
    }

Even onmySignal doesn't work. One has to capitalize the first alphabet even if its declaration doesn't have uppercase first latter.

Christian Ehrlicher

@johndummy said in Couldn't catch signal from Cpp in QML:

One has to capitalize the first alphabet even if its declaration doesn't have uppercase first latter

Not that this is documented somewhere.