Using QSerialPort in multi widget application

mrjj

@viniltc
Hi
The Instance pointer is where you create the MainWindow.
often in main.cpp

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w; <<< that is the instance
    w.show();

    return a.exec();
}

However, do you really need to share the actual serial class?
You could also define some new signals in MainWindow and
connect other classes to these signals to allow to send via serial.
Or you could move serial to its own class and both mainwindow and OtherClass could use it via signals.

JonB

@viniltc
I'm with @mrjj :

Or you could move serial to its own class and both mainwindow and OtherClass could use it via signals.

in that I'd put it into its own class file. Though I don't think you then need to communicate with it via signals, that may be a bit more work then you're used to. To me, your serial port object just does not particularly belong as a member of your MainWindow (either instance or class) at all.

What is MainWindowInstancePointer in my case? This is my mainwindow.h

It's your public QSerialPort *serial1;. Following what I've said above, because you're making your QSerialPort a member of your MainWindow instance that would mean your other module needs to find & access the current main window instance in order to access that object.

To make what you've currently work dirtily without doing that, make your declaration (.h file) and definition (.cpp file) have static (I don't do C++ daily so I don't offer the exact code). That will allow you to access it from the other module via MainWindow::serial. [I assume you just have typos where sometimes your variable is named serial and sometimes serial1.]

I still don't recommend this actual way of doing it, static is not great these days. My thought as I said would be singleton class/object.

SGaist

Hi,

As my fellows already wrote: don't implement it that way. You should first explain what exactly your other widgets are going to do with the serial port.

viniltc

@JonB , @mrjj , @SGaist
Thanks a lot, guys. I got your points.

viniltc

Hi,
As per the previous suggestion I was trying to create a singleton class for my serial port module. I have one serial port that needs to be able to read and write in multiple forms.

My serial module class as follows :

#include "tetraserial.h"

tetraSerial::tetraSerial(QObject *parent) : QObject(parent)
{

   serialObject = new QSerialPort();
   serialObject->setPortName("com5");
   serialObject->setBaudRate(1000000);
   serialObject->setDataBits(QSerialPort::Data8);
   serialObject->setParity(QSerialPort::NoParity);
   serialObject->setStopBits(QSerialPort::OneStop);
   serialObject->setFlowControl(QSerialPort::HardwareControl); /
   serialObject->open(QIODevice::ReadWrite);
    
}

and my serial.h as follows

#ifndef TETRASERIAL_H
#define TETRASERIAL_H

#include <QObject>
#include <QtSerialPort/QSerialPort>
#include <QtSerialPort/QSerialPortInfo>
#include <QDebug>

class tetraSerial : public QObject
{
    Q_OBJECT
public:
    explicit tetraSerial(QObject *parent = nullptr);
  static QSerialPort *serialObject;

signals:

public slots:
};

#endif // TETRASERIAL_H

I was trying to access serialObject from MainWindow as follows:

 connect(tetraSerial::serialObject, SIGNAL(readyRead()), this, SLOT(serialRecived()))

I'm getting an error saying undefined refernce to 'tetraSerial::serialObject'

what I'm doing wrong here?

JonB

@viniltc
With the usual proviso that my C++ is shaky, and I'm not sure whether it could cause the error if it's against the connect() line as opposed to from the linker, but: you do not show, but in your tetraserial.cpp (not .h) have you placed the definition static QSerialPort *tetraSerial::serialObject; somewhere?

viniltc

@JonB said in Using QSerialPort in multi widget application:

static QSerialPort *tetraSerial::serialObject;

@JonB
The error is thrown from the mainWindow.cpp

Also, I can't place static QSerialPort *tetraSerial::serialObject; in the class definition in tetraserial.h either ; it says extra qualification on member 'serialObject'

Any thought!?

JonB

@viniltc
I did state that line was specifically not to be put in tetraserial.h, it belongs in tetraserial.cpp if you do not already have it there.

I don't know now about your error in mainWindow.cpp --- unless you have failed to include tetraSerial.h there, you wouldn't have failed to do that would you??

viniltc

@JonB

I modified the .cpp file as follows:

#include "tetraserial.h"

 QSerialPort *tetraSerial::serialObject;


tetraSerial::tetraSerial(QObject *parent) : QObject(parent)
{

   serialObject = new QSerialPort(this);
   serialObject->setPortName("com5");
   serialObject->setBaudRate(1000000);
   serialObject->setDataBits(QSerialPort::Data8);
   serialObject->setParity(QSerialPort::NoParity);
   serialObject->setStopBits(QSerialPort::OneStop);
   serialObject->setFlowControl(QSerialPort::HardwareControl);
   serialObject->open(QIODevice::ReadWrite);

}

I can't defineQSerialPort *tetraSerial::serialObject as static because it is allowed only inside the class definition.

Now It is building but I'm getting a runtime error, it says in the console:

cannot connect <null>::readyReady() Mainwindow::serialRecived

my connect statement in the main as follows:

connect(tetraSerial::serialObject, SIGNAL(readyRead()), this, SLOT(serialRecived()));

Any suggestion??

JonB

@viniltc

cannot connect <null>::readydata() Mainwindow::serialRecived

readydata() or readyRead()? Did you copy & paste the error message?

TBH this is getting to be serious C++ stuff, so I ought bow out. You need someone who knows his C++ better than I!

viniltc

@viniltc said in Using QSerialPort in multi widget application:

cannot connect <null>::readydata() Mainwindow::serialRecived
@JonB
Sorry my bad yes, that's readyRead()
Btw thanks a lot @JonB for your suggestions.

viniltc

@SGaist @mrjj

Any help would be welcome..

SGaist

There's no need to make your serial port static.

You don't check whether the open call was successful.

mrjj

hI
Also, im a little concerned by sharing the serial idea.
Its fine for writing to it, however, if you connect say 3 other classed to
readyRead() signal, they all get the signal but whom of them will then read the data ?
and how will you know if that class was the intended receiver of the data?

It would help if you explained more what the app does and its intended design.

viniltc

@SGaist

If it's non-static, I'm getting an error saying invalid use of non-static data member 'serialObject

The program is getting crashed from the mainWindow itself

connect(tetraSerial::serialObject, SIGNAL(readyRead()), this, SLOT(serialRecived()));

Can't find what's wrong with my class definition.

jsulm

@viniltc You need to use an instance of tetraSerial class

viniltc

@mrjj

It is a GUI to communicate with an FTDI based serial device.

There will be setup stages having three windows. At the end of setup, the GUI should send a 'config file' to the serial device (say CPU -A)
During those setup stages, GUI should also read the serial device to get real-time updates of some sensors connected to the device (CPU-B). Also writing to some registers of the device.
For example, I have three windows - window1, window2, window3. The 'config file' will be sent at window 3. The user will be seeing some sensor values in window2 and updating its parameters by writing into some short registers.

All the above operations will be done through a single FTDI based serial (UART).
So what I need is to get an instance of opened serial port' in any of those windows to read or write

Any thoughts?

viniltc

@jsulm

I try to modify the class file as follows:

#include "tetraserial.h"


tetraSerial::tetraSerial(QObject *parent) : QObject(parent)
{

}

void tetraSerial::serialOpen()
{
    
    serialObject = new QSerialPort();
    serialObject->setPortName("com5");
    serialObject->setBaudRate(1000000);
    serialObject->setDataBits(QSerialPort::Data8);
    serialObject->setParity(QSerialPort::NoParity);
    serialObject->setStopBits(QSerialPort::OneStop);
    serialObject->setFlowControl(QSerialPort::HardwareControl);
    serialObject->open(QIODevice::ReadWrite);
    
    
}

void tetraSerial::serialRecived2()
{
    
}

and the header as follows:

#ifndef TETRASERIAL_H
#define TETRASERIAL_H

#include <QObject>
#include <QtSerialPort/QSerialPort>
#include <QtSerialPort/QSerialPortInfo>
#include <QDebug>
#include <QFile>
#include <QMessageBox>

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

  //  static QSerialPort *serialObject;
  QSerialPort *serialObject;
  
  void serialOpen()
    

signals:

public slots:
          void serialRecived2();
};

Then I use this in the main as:

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow) 
{
    ui->setupUi(this);
 
  tetraSerial serial;
  serial.serialOpen();
  
  connect(serial, SIGNAL(readyRead()), this, SLOT(serialRecived2()));


}

I've got an error says:

no matching member function for call to 'connect'

I don't understand why the connect function can't find a matching function.

jsulm

@viniltc What is serial in

connect(serial, SIGNAL(readyRead()), this, SLOT(serialRecived2()));

?
It needs to be a pointer:

connect(&serial, SIGNAL(readyRead()), this, SLOT(serialRecived2()));

viniltc

@jsulm

I'm getting a runtime error saying
QObject::connect: No such signal tetraSerial::readyRead() in ..\serialPortTest\mainwindow.cpp:54 QObject::connect: (receiver name: 'MainWindow')

I already configured the serial port in the tetraSerial class as shown above. What might be the cause?

Also
I'm a bit confused about where to define signals and slots. As you can see I've opened the device in my tetraSerial class in a method called serialOpen. Now I want to communicate with for example two forms. When I press Read button in form1 , the data shluld be displayed on a textbox in form 1. In form 2, when I press Write, it shluld write a file into the opened device.

My confusion where should I define signals and slots and where should I connect them?