Using QTimer with signal

Alpkan

as you can on the picture when i am trying use qtimer with my signal it's not letting me to do

is there any solution for it

jsulm

@Alpkan add this to []
Reason: the signal belongs to the instance of the class, so you have to capture this in your lambda.

Alpkan

thanks for your answer, it's solved the problem

Alpkan

@jsulm said in Using QTimer with signal:

@Alpkan add this to []
Reason: the signal belongs to the instance of the class, so you have to capture this in your lambda.

@jsulm that is solved the warnings but now when i run the code, there no message on the screen

jsulm

@Alpkan Is a slot connected to the mySignal signal?
And there is another issue in your code: timer is a LOCAL variable which is destroyed when send() terminates.

Alpkan

"signaltaker.h"

#ifndef SIGNALTAKER_H
#define SIGNALTAKER_H

#include <QObject>
#include <QWidget>
#include <QDebug>

class signaltaker:public QObject
{
Q_OBJECT
public:
explicit signaltaker(QObject *parent = nullptr);

signals:

public slots:
void onMessage(QString message);
};

#endif // SIGNALTAKER_H

"signaltaker.cpp"
#include "signaltaker.h"

signaltaker::signaltaker(QObject *parent) : QObject(parent)
{

}

void signaltaker::onMessage(QString message)
{
qInfo() << message;

}

"widget1.h"
#ifndef WIDGET1_H
#define WIDGET1_H

#include <QObject>
#include <QWidget>
#include <QDebug>

class widget1 : public QObject
{
Q_OBJECT
//here - private
public:

//public
explicit widget1(QObject *parent = nullptr);

void send();

signals:
void mySignal(QString message);

public slots:

};

#endif // WIDGET1_H

"widget1.cpp"
#include "widget1.h"
#include <QDebug>
#include <QtCore>
#include <QTimer>

widget1::widget1(QObject *parent) : QObject(parent)
{

}

void widget1::send()
{
QTimer timer;
QObject::connect(&timer, &QTimer::timeout, this { emit mySignal("bbbbbbb"); });
timer.start(2000);

}

"widget2.h"
#ifndef WIDGET2_H
#define WIDGET2_H

#include <QObject>
#include <QWidget>

class widget2:public QObject
{
Q_OBJECT
public:

explicit widget2(QObject *parent = nullptr);

void send();

signals:
void mySignal(QString message);

public slots:
};

#endif // WIDGET2_H

"widget2.cpp"
#include "widget2.h"
#include <QDebug>
#include <QTimer>
#include <QtCore>

widget2::widget2(QObject *parent) : QObject(parent)
{

}

void widget2::send()
{
emit mySignal("aaaaaaa");

}

"main.cpp"
#include <QCoreApplication>
#include <QtCore>
#include <QTimer>
#include "widget1.h"
#include "widget2.h"
#include "signaltaker.h"

int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);

widget1 obj1widget1;
widget2 obj2widget2;
signaltaker objsignaltaker;


QObject::connect(&obj1widget1, &widget1::mySignal, &objsignaltaker, &signaltaker::onMessage);
QObject::connect(&obj2widget2, &widget2::mySignal, &objsignaltaker, &signaltaker::onMessage);

obj1widget1.send();
obj2widget2.send();





return a.exec();

}

there is no another issue when i build, it seems every thing is right.

jsulm

@Alpkan said in Using QTimer with signal:

there is no another issue when i build, it seems every thing is right.

Not everything. As I said: timer is a LOCAL variable.

void widget1::send()
{
    QTimer timer; // timer is a local variable inside send()
    QObject::connect(&timer, &QTimer::timeout, this { emit mySignal("bbbbbbb"); });
    timer.start(2000); // It gets destroyed just after this line!
}

Please read about scope in C++ to avoid such mistakes.
To fix the issue make timer a class variable insider widget1, or allocate it on the heap using "new".

Alpkan

@jsulm i understand, thanks for help. I will do it.

J.Hilk

@Alpkan I think you may want this as a single shot timer, if thats the case:

QTimer::singleShot(2000, this , [=]()->void{ emit mySignal("bbbbbbb"); });

Alpkan

I now singleshot is working but i want to send message every 10 second with qtimer :)

J.Hilk

@Alpkan said in Using QTimer with signal:

I now singleshot is working but i want to send message every 10 second with qtimer :)

then you'll need a QTimer as a class member and/or one created on the heap
and you need to change your timeout from 2 seconds to 10, of course :D