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Signals passing pointer

  • I wish to pass a pointer by singals and slots.

                    target: device

    The device issues a ImagebufCreated signals which carries a pointer to a buff. pFrame is a char* pointer.

    The real_time_image component catch the signal to do somthing.

    But this gives a runtime error:
    qrc:/qml/main.qml:149: Error: Unknown method parameter type: char*

    When I change the pointer pFrame to int, the connection works fine. I also experimented with QObject::Connect, signals can carry pointers, but when it is defined in QML Connection type, the engine does not recognize it.

    Is it a bug or is there a better practice than passing pointers?


    Update: Currently, I walk around this problem by reinterpret char* to int, passing it, then reinterpret it back. It works but Soooooo ugly.

  • @mondo said in Signals passing pointer:

    I expect you need to register your c++ type that gets passed to your QML engine (pFrameBuf)

    However, have you seen :

    You might find it easier to not use char*'s.

  • @6thC
    The idea to register any pointer type I use is still not that elegant.

    QbyteArray solves my problem here, it can be passed in signals.
    I'll just need some time to adapt to qt native types.

    Thanks for you help mate.

  • Just have to register the class type (not as a pointer).

    It just needs know about your class type and what to refer to it as.

    // register T
    qmlRegisterUncreatableType<ClassT>("MyClassT"    ,1,0,"MyClassT", "");
    // set QML instance to context
    context->setContextProperty(QLatin1Literal("MyClassTIstnaceNamedCpp"), &myCppUncreatableObject);

    // QML

    function something(){
      // call cpp something
    // QML Connection also:
    Connections {
      target: MyClassTIstnaceNamedCpp;
      onSomething: {
        print("cpp something happened");

    Sorry it's not all complete but ... hopefully gives you a peek. It's probably possible much easier.

    You can also pass pointers to objects and have QML dynamically create registered CPP class instances - my example has cpp instanced objects and named context... sorry if I'm not explaining very well but I am actually procrastinating myself... on a tight deadline. I shouldn't! Anyhow, good luck.

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