signal/slot between two different classes

[dziko147]

@jsulm be sure that I tried to recover on my own . if you can't/do not want help me ,please ignore this topic :)

[jsulm]

@dziko147 said in signal/slot between two different classes:

be sure that I tried to recover on my own

Then please show what you tried and say what went wrong if you want to get meaningful help...

[dziko147]

@jsulm ok I tried this actually

in //MainWindow.h

signals:
    void canDeviceChanged(int value);

in //MainWindow.cpp

connect(this, SIGNAL(canDeviceChanged(int value )),&back, SLOT(statuspican(int value)));


if (m_canDevice)
    emit canDeviceChanged(1); 

in backend.h

public slots:
    void statuspican(int value);

in backend.cpp

void Backend::statuspican(int value)
{
qDebug() << "from Mainwindow :" << value;
}

[KroMignon]

@dziko147 said in signal/slot between two different classes:

connect(this, SIGNAL(canDeviceChanged(int value )),&back, SLOT(statuspican2(int value)));

Have you read the link a give you at least 5 times?
This can not work ==> https://doc.qt.io/qt-5/qobject.html#connect

EDIT
What is statuspican2?
According to your code, the slot name is statuspican

[jsulm]

@dziko147 said in signal/slot between two different classes:

connect(this, SIGNAL(canDeviceChanged(int value )),&back, SLOT(statuspican2(int value)));

Remove "value". Old style connect does only contain the parameter type, not its name.
But you should really switch to new Qt5 connect syntax - if you then do something wrong you will get a compiler error. With old style connect you only get a runtime warning if connect fails.

[dziko147]

so logically it should works , there is no syntax error ! ?

[jsulm]

@dziko147 Did you read what I and @KroMignon wrote?

[KroMignon]

@dziko147 said in signal/slot between two different classes:

so logically it should works , there is no syntax error ! ?

Are you jocking?

Nothing is correct:

• the slot name is wrong
• the SIGNAL() syntax is wrong ==> only signal signature means: signal name and parameter types
• the SLOT() syntax is wrong ==> only slot signature means: slot name and parameter types

[dziko147]

@KroMignon ok could you provide a connect implementation to solve this .

i am blocked since 3 days :/

[Christian Ehrlicher]

@dziko147 said in signal/slot between two different classes:

ok could you provide a connect implementation to solve this .

@jsulm already told you what's wrong and you should switch over to the new signal/slot syntax so you get proper compile time errors instead during runtime.

[KroMignon]

@dziko147 said in signal/slot between two different classes:

ok could you provide a connect implementation to solve this .
i am blocked since 3 days :/

Can you read?

@jsulm told you what to do:

Remove "value". Old style connect does only contain the parameter type, not its name.

And in Qt documentation:

Note that the signal and slots parameters must not contain any variable names, only the type. E.g. the following would not work and return false:

// WRONG
QObject::connect(scrollBar, SIGNAL(valueChanged(int value)),
             label, SLOT(setNum(int value)));

// CORRECT
QObject::connect(scrollBar, SIGNAL(valueChanged(int)),
            label,  SLOT(setNum(int)));

I cannot believe this take 3 days to understand.

[dziko147]

@KroMignon even i remove the "value" it doesn't works .
I didn't understand why .
No error but the application spits .

[KroMignon]

@dziko147 said in signal/slot between two different classes:

No error but the application spits .

Why not using the debugger to find out why your application crash?

And in you connect:

connect(this, SIGNAL(canDeviceChanged(int)),&back, SLOT(statuspican(int)));

What is back?
Where is it defined?

[jsulm]

@dziko147 Next thing to check: what does connect() call return?

qDebug() << connect(this, SIGNAL(canDeviceChanged(int)),&back, SLOT(statuspican(int)));

Next: did you make sure that the signal is actually emitted?

if (m_canDevice) {
    qDebug() << "Emit signal";
    emit canDeviceChanged(1);
}

[dziko147]

@jsulm

qDebug() << connect(this, SIGNAL(canDeviceChanged(int)),&back, SLOT(statuspican(int)));

return true .

And the signal is emmited

[SGaist]

Hi,

@dziko147 said in signal/slot between two different classes:

@jsulm

qDebug() << connect(this, SIGNAL(canDeviceChanged(int)),&back, SLOT(statuspican(int)));

return true .

And the signal is emmited

Where is back defined ?
Any chances that this is a function local variable that is destroyed at the end of it ?

[dziko147]

@SGaist

Backend is my second class . the class which i want to get data in .
So back is an instance of Backend .

So i defined like this :

Backend back; 

[SGaist]

The question is: where is it defined ?

[dziko147]

@SGaist

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    m_ui(new Ui::MainWindow),
{
    m_ui->setupUi(this);
    
    Backend back ;
connect(this, SIGNAL(canDeviceChanged(int)),&back, SLOT(statuspican(int)));

[SGaist]

That's what I suspected: back is destroyed at the end of the constructor.