same signal-slot connection in two windows

russjohn834

Hi all,

I just noticed this thing if I call both my Settings and Patients from my main the connection is successful (see below)

#include <QApplication>

tetra_grip_api api;

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

    api.openSerialPort();

    QObject::connect(api.serial, SIGNAL(readyRead()), &api, SLOT(readData()));
    QObject::connect(api.serial, SIGNAL(error(QSerialPort::SerialPortError)),&api, SLOT(ErrorHandler(QSerialPort::SerialPortError))); // error handling

    Settings w(nullptr);
    w.show();

    Patients v(nullptr); //---------> this makes connection successfull
    v.show();

    return a.exec();
}

but instead, if I call Patients from Settings even though the connection is successful im not getting the expected output.

My signal source api is a global variable which is initialized in the main as shown above.
So constructing both classes in the main makes connection ok and I'm gettting expected output. But if I call one window from other makes connection true but my slot is not being called at all.

What is the reason for this?

JonB

@russjohn834
If you're asking me to guess, show how you gain access to tetra_grip_api api; from Settings/Patients? In these cases where do you do the connect()s from? And, how do you know your connect()s are successful?

SGaist

Hi,

@russjohn834 said in same signal-slot connection in two windows:

QObject::connect(api.serial, SIGNAL(readyRead()), &api, SLOT(readData()));
QObject::connect(api.serial, SIGNAL(error(QSerialPort::SerialPortError)),&api, SLOT(ErrorHandler(QSerialPort::SerialPortError))); // error handling

Since serial is internal to api why don't you connect it in the constructor of your tetra_grip_api class ?

russjohn834

@JonB

This is how I make the connection in Settings.

Settings::Settings(QString patientLabel, QWidget *parent) : QMainWindow(parent)
    , ui(new Ui::Settings)
{
    ui->setupUi(this);
   
    connect(&api, &tetra_grip_api::tetraGripEvent,this, &Settings::eventHandler);
}

Connection is successfull (qDebug()<<connect(....) gives TRUE) also the a QLabel and an LED in the eventHandler slot works perfectly.

In the same way I try to connect in the Patients:

Patients::Patients(QWidget *parent) : QMainWindow(parent)
    , ui(new Ui::Patients)
{
    ui->setupUi(this);
   
    connect(&api, &tetra_grip_api::tetraGripEvent,this, &Patients::eventHandlerTwo);
}

here connection is successfull (qDebug()<<connect(....) gives TRUE) but the a QLabel and an LED in the eventHandlerTwo are not working.

JonB

@russjohn834
How do I know &api refers to the same, global, initialized api instance in both cases?
And I see nothing in code about any QLabel in either case, not mentioned by you before...
You have to supply the necessary/relevant code if you want people to help.
Use a debugger to make sure whether slots are being hit.

russjohn834

@JonB

I thought api should be known and accessible to all classes if intialized as global in the main.cpp

#include <QApplication>

tetra_grip_api api; //-------------> api instance

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

    api.openSerialPort();
    QObject::connect(api.serial, SIGNAL(readyRead()), &api, SLOT(readData()));
    QObject::connect(api.serial, SIGNAL(error(QSerialPort::SerialPortError)),&api, SLOT(ErrorHandler(QSerialPort::SerialPortError))); // error handling


    Settings w(nullptr);
    w.show();

    return a.exec();
}

Correct me if I'm wrong.

JonB

@russjohn834
Your Settings & Patients classes are defined in a different source module from main.cpp, right? So how do they gain access to reference the api symbol in order to compile?

 connect(&api, &tetra_grip_api::tetraGripEvent,this, &Patients::eventHandlerTwo);

I am having to tease out each bit of relevant information, one at a time....

russjohn834

@JonB
Correct. I actually did not do anything other that making apiinstance as global in main.cpp. That might be the issue. But dont know how to proceed. How do I make Patients classes know about global api instance?

jsulm

@russjohn834 You should avoid global variables as much as possible.
Just pass the pointer to api to Settings & Patients constructors...

jazzco2

Did you ensure that the connection in Patients is done before the signal tetra_grip_api::tetraGripEvent is emitted? Some qDebugs around connection, in the very first line of Patients::eventHandlerTwo and in the deconstructor of Patients should help to prove that.

JonB

@russjohn834 said in same signal-slot connection in two windows:

@JonB
Correct. I actually did not do anything other that making apiinstance as global in main.cpp. That might be the issue. But dont know how to proceed. How do I make Patients classes know about global api instance?

I truly, truly do not understand. You said your program runs but does/does not behave properly in the cases you mentioned. I asked how you can even compile your Settings/Patients modules/.cpp source files which contain the line connect(&api, ..., when api is defined in main.cpp? From what you have said/shown they should error at compile-time with a "No such variable: api" message. So I will leave others to help, who obviously understand your source code better than I.

jazzco2

@JonB Yes, that's interesting. You can't include main.cpp in Settings or in Patients. So main.cpps line

tetra_grip_api api; //-------------> api instance

isn't visible anywhere!

jazzco2

@russjohn834 If you are using QtCreator: When you go on the &api in your connect statements in both Settings and Patients and press F2 - where does it lead you to?

russjohn834

@jazzco2

From both Settings and Patients , &api leads me here:

#ifndef TETRA_GRIP_API_H
#define TETRA_GRIP_API_H

#include <QObject>
#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <QLabel>
#include <QMessageBox>
#include <QTimer>

#define _CRT_SECURE_NO_DEPRECATE

class tetra_grip_api : public QObject
{
    Q_OBJECT

public:
    explicit tetra_grip_api(QObject *parent = nullptr);

    #define MAX_CONFIG_FILE_LENGTH (10000)

     void static send_config_file(QByteArray config, bool nonvolatile);
     void static send_long_register(uint8_t, uint32_t, uint8_t *);
     void static stimulation_set_current(unsigned int, unsigned int);

     QSerialPort *serial = nullptr;

     QTimer autoConnectionTimer;
     bool tryToAutoconnect;

signals:

     void tetraGripEvent(STIM_GUI_TOPIC_T topic, uint8_t reg, uint32_t value);



public slots:

     void openSerialPort();
     void closeSerialPort();
     void readData();


private slots:

     void ErrorHandler(QSerialPort::SerialPortError error);

private:

        QString comPortName;

};

extern tetra_grip_api api;  //----------> it leads me here

#endif // TETRA_GRIP_API_H

jsulm

@russjohn834 said in same signal-slot connection in two windows:

extern tetra_grip_api api;

You really should not do it like this. Pass pointer to the constructors of the classes which need it.

JonB

@jazzco2 said in same signal-slot connection in two windows:

@JonB Yes, that's interesting. You can't include main.cpp in Settings or in Patients.

No, but you might be including main.h, and maybe you have extern tetra_grip_api api; there, that's the sort of thing I was trying to understand. Which finally you have shown is actually in tetra_grip_api.h, which I guess you are including into each of them?

For the line there

extern tetra_grip_api api;

does the docs for tetra_grip_api say you are responsible for defining tetra_grip_api api; yourself like you have done in main.cpp, or does it say they (the library) are defining that global instance and you are supposed to use their instance?

jazzco2

@russjohn834 Yes, pass the pointer - and then your api can be a local variable in main. No need to define it outside as main lives as long as the application is running.

russjohn834

@jazzco2

Could you give me an example to show how do I pass a pointer to the constructor of the classes? for ex. if I need to use it in in Settings and Patients classes ?

jsulm

@russjohn834 said in same signal-slot connection in two windows:

Could you give me an example to show how do I pass a pointer to the constructor of the classes?

Well

tetra_grip_api api;
Settings settings(&api);

Of cource you have to change the constructor, but this is C++ basic stuff.

russjohn834

@JonB

it did not mention anything like that. My primary requirement is to use tetra_grip_api(which is a class containing all serial communication objects) instance in every form class. That's why I made it global, but now I realize it's not a good way of programming!