same signal-slot connection in two windows

[russjohn834]

Hi All,

I have two windows (QMainWindow), say Settings and Patients.

There is a signal - slot connection in the Settings as follows:

connect(&api, SIGNAL(batteryEvent(STIM_GUI_TOPIC_T, uint8_t, uint32_t )), this, SLOT(eventHandler(STIM_GUI_TOPIC_T , uint8_t , uint32_t )));

here eventHandler controls an LED battery status button

In the Settings window this works fine. Now I need to do the same thing on Patients window (controls an LED), Pateints is constructed from Settings. I trie doing the same connection (below) in the Patients window but that seems not working.

connect(&api, SIGNAL(batteryEvent(STIM_GUI_TOPIC_T, uint8_t, uint32_t )), this, SLOT(eventHandlerTwo(STIM_GUI_TOPIC_T , uint8_t , uint32_t )));

Any idea what am I doing wrong here?

[mrjj]

@russjohn834
Hi
Check if the connect return TRUE
Also, make sure none of the objects runs out of scope
I can see you use & on the API class so make sure its not a local variable.

Also consider using the new connect syntax as that catches more errors
https://wiki.qt.io/New_Signal_Slot_Syntax

Also, show the code for the settings things that don't work.
Classic errors include creating a new instance to connect instead on the one on screen or
using a local variable that won't live long enough to send any signals.
But it could also be something else so we need to see the full code for the creation and connection to have
a chance to say where it went wrong.

[Pablo J. Rogina]

@russjohn834 I wonder if you need a different approach here.
Are those QMainWindows at the same level? I mean, are they created in some "higher level" container object?
If so, maybe you need to move the handling of the battery event and LED on/off task there. I'm thinking what will happen if you need to add 2 more windows, are you going to connect the api and LED handling in those new windows as well? and then you're asked to add 2 more windows... it seems not good for app maintenance...

[russjohn834]

@mrjj @Pablo-J-Rogina Thanks.

just a quick question, how can I switch following into the new Signal-slot syntax?

  connect(&api, SIGNAL(tetraGripEvent(STIM_GUI_TOPIC_T, uint8_t, uint32_t )), this, SLOT(eventHandler(STIM_GUI_TOPIC_T , uint8_t , uint32_t )));

here api is global variable

[Cobra91151]

@russjohn834

Hello!

The new Signal-slot syntax will be like this:

connect(this, &Test::tetraGripEvent, this, &Test::eventHandler);

Note: this is just a test example. Where the Test is your current class and it emitting a signal and receiving it. Also, you can do it using lambda.

connect(this, &Test::tetraGripEvent, [this](STIM_GUI_TOPIC_T a, uint8_t b, uint32_t c) {
    eventHandler(a, b, c);
});

You need to provide more info about the api global variable, where and how you have initialized it?

[russjohn834]

@Cobra91151 Thank you.

I define the instance of my API class in the main as follows:

tetra_grip_api api; ------------>class instance

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

    api.openSerialPort();
    QObject::connect(api.serial, SIGNAL(readyRead()), &api, SLOT(readData()));

    Settings w(nullptr);
    w.show();
    return a.exec();
}

In this case, how do I switch the following expression into the new signal-slot syntax?

connect(&api, SIGNAL(tetraGripEvent(STIM_GUI_TOPIC_T, uint8_t, uint32_t )), this, SLOT(eventHandlerTwo(STIM_GUI_TOPIC_T , uint8_t , uint32_t )));

[jazzco2]

If this is of your class Settings the following should work.

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

Otherwise replace the second class by the correct one.

[russjohn834]

@jazzco2 Thanks a lot.

The new connect syntax seems ok. It did not complain about anything. But I'm not getting the expected output. Just to summarize.

I'm calling QMainWindow Patients from Settings. In the Patients constructor, I did connect as follows:

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

When I put a breakpoint in the connect statement, it did not went into the eventHandlerTwo slot. which means something wrong in the way I did the connection.

where api is global variable.

eventHandlerTwo is a public slot:

void Patients::eventHandlerTwo( STIM_GUI_TOPIC_T topic, uint8_t reg, uint32_t value)
{
    if (topic==TOPIC_STIMULATOR)
    {
        switch(reg)
        {
        case STIM_REG_BATTERY_CAPACITY_REMAINING:

            if(value<86)
                ui->qLed_p2->setOnColor(QLed::Red);
            else
                ui->qLed_p2->setOnColor(QLed::Green);
                ui->qLed_p2->setValue(true);
            break;
        }
    }
    ui->label_batteryVal->setText(QString::number(value));
 }

Patients being called from Settings as follows:

void Settings::on_pushButton_patients_clicked()
{

    hide();
    stagetwo = new Patients(this);
    stagetwo -> show();
}

Any thoughts?

[Christian Ehrlicher]

So where do you call your connect() statement?

[JonB]

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

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

When I put a breakpoint in the connect statement, it did not went into the eventHandlerTwo slot. which means something wrong in the way I did connection.

What do you mean? When the connect statement is executed it will not cause any entry into Patients::eventHandlerTwo, that only comes when the signal is later emitted.

[russjohn834]

@Christian-Ehrlicher

Connect is called as in the following:

Patients::Patients(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::Patients)
{
    ui->setupUi(this);


    this->setStyleSheet("background-color: white;");
    this->setFixedSize(this->width(),this->height());



    connect(&api, &tetra_grip_api::tetraGripEvent,this, &Patients::eventHandlerTwo); //--->connect is called here
    
// Setup table
    ui->tableWidget->setColumnCount(5);
    ui->tableWidget->setHorizontalHeaderLabels(QStringList{"Patient ID","Name", "Surname", "LastSession", "Note"});
    ui->tableWidget->horizontalHeader()->setSectionResizeMode(QHeaderView::Stretch);
    ui->tableWidget->setSelectionBehavior(QAbstractItemView::SelectRows);



     QString path = QCoreApplication::applicationDirPath()+"/data/";



    QStringList qdiFilter("*.xml");


    QDirIterator qdi( path, qdiFilter, QDir::Files);
    while (qdi.hasNext())
    {
        parseDataEntry(qdi.next());
    }

}

[russjohn834]

@JonB

I'm connecting with the same signal in the previous window , so do I need to disconnect that and connection to use the same signal in with a new slot?

Basically in Settings window this works:

 connect(&api, &tetra_grip_api::tetraGripEvent,this, &Settings::eventHandler); //--> slot is eventHandler

But in Patients this is not working:

   connect(&api, &tetra_grip_api::tetraGripEvent,this, &Patients::eventHandlerTwo);//--->Slot is eventHandlerTwo

[JonB]

@russjohn834
So I now take it you mean you find the slot does not get entered, not the the connect fails?

No, you do not have to disconnect, a signal may have any number of slots attached. Though if a previously-attached slot does not return, or misbehaves like if the slot instance is no longer around, it is possible the second slot might not get called.

So if debugging what is going you might be advised to temporarily not connect the Settings slot, just the Patients slot and concentrate on sorting that out. It is not possible to say from what you have posted why one slot works and the other does not.

[russjohn834]

@JonB Thank you. I tried to connect only the Patients slot but cant see where I'm wrong..

Patients window is opened from Settings as given below:

void Settings::on_pushButton_patients_clicked()
{

    hide();
    stagetwo = new Patients(this);
    stagetwo -> show();
}

Where stagetwo is public

public:
     Settings(QString,QWidget *parent = nullptr);
    ~Settings();
     Patients *stagetwo;

Anything wrong I'm doing here!?

[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.