qmlRegisterSingletonType object emit signal. Problem with qml slot connection

edoardo.videx

Hi, i've a qmlRegisterSingletonType object that's can emit two signals. I want capture this signal with slots in QML.

This is the main:

qmlRegisterSingletonType<SDK2220_SysLog>("VidexMessageBox",0,1,"SysLogSocket",Get_SysLogManager);

This is my class :

class SDK2220_SysLog :public QThread
{
    Q_OBJECT


    Q_PROPERTY(NOTIFY set_logger_okay CONSTANT)

    Q_PROPERTY(NOTIFY add_new_item CONSTANT)

public:

    SDK2220_SysLog();

    SDK2220_SysLog(QHostAddress *addr,int port);


private slots:

    void on_start_thread_emitted();

signals:

    Q_INVOKABLE void set_logger_okay();

    Q_INVOKABLE void add_new_item();


};

and this is a QML CODE:

    Connections{
        target: SysLogSocket

        onSet_logger_okay:{
            setting.saveFilterChecked("SRV2220",2)
            console.log("33333333333333333333333333333333333333333333333333333")
        }
    }

When in the cpp code i emit set_logger_okay, it doesen't captured to QML.

Someone can help me?

sierdzio

Check if there is any warning printed at runtime - perhaps Connections did not really connect?

Also, try removing the Q_PROPERTY notifiers - just having signals is enough. And you don't need to marks signals as Q_INVOKABLE, they already are invokable.

J.Hilk

@edoardo-videx said in qmlRegisterSingletonType object emit signal. Problem with qml slot connection:

Get_SysLogManager

please show us your singleton instance function

edoardo.videx

@J-Hilk

static QObject * Get_SysLogManager(QQmlEngine * engine, QJSEngine *scriptEngine)
{


    Q_UNUSED(engine);
    Q_UNUSED(scriptEngine);

    static SDK2220_SysLog * s_instance = new SDK2220_SysLog();

    QQmlEngine::setObjectOwnership(s_instance, QQmlEngine::CppOwnership);

    return s_instance;
}

J.Hilk

@edoardo-videx alight
and how and when do you emit the signal from c++ ?

edoardo.videx

@J-Hilk

Inside the method

void SDK2220_SysLog::run()

i do this :

if( evt->cmd == SDK2220_PROTOCOL_CMD_SET_LOGGER)
{
      emit set_logger_okay();
}

sierdzio

Are you 100% sure the signal is actually being emitted? Throw in some debug message to verify.

sierdzio

Also, does that run() method leave some space for even loop to propagate the signal?

KroMignon

@edoardo-videx I see SDK220_SysLog got a slot/method called run(). Is it sub-classing QObject or QThread?
To made signal/slots works, a QObject class must be running in a thread which implements a event loop... If you have sub-classed QThread and then also the QThread::run() method, then there will be no event queue to handle the signal!

You can try to create a temporary QEventLoop to handle your signal:

if( evt->cmd == SDK2220_PROTOCOL_CMD_SET_LOGGER)
{
    QEventLoop loop;
    Q_UNUSED(loop)
    emit set_logger_okay();
}

In general, it is not a good practice to sub-class QThread, it is bette to create a worker class and to move this class to new thread.
Take a look at following links for more details:
http://blog.debao.me/2013/08/how-to-use-qthread-in-the-right-way-part-1/
https://www.toptal.com/qt/qt-multithreading-c-plus-plus

jsulm

@KroMignon said in qmlRegisterSingletonType object emit signal. Problem with qml slot connection:

QEventLoop loop;
Q_UNUSED(loop)

I don't even know what this loop is supposed to do as exec() isn't called here