QtCreator C++ create thread in main window - qt

Question

I'm building up an application, which receives data over the serial interface. So i implemented a class for the serial handling, which can successfully receive and send data. Now I try to move the data to the UI, to give it out to a console, but I need a thread for that and it seems more difficult than I expected.
So somehow I need to define a thread and start it at the beginning of the UserInterface creation and this thread should then poll a function for new data. I researched about creating a thread and connect it to a callback function, but it is always related to create a class, that inherits from QThread, which I cannot do for the Main UI.
How should I define a thread inside the Main UI, which I can use then to poll a function?
Edit: As recommended, a thread is not necessary here, but I don't know how to call a function inside a class without an object. In the mainWindow class, where all the UI stuff like labels and buttons sits, I created an object for serial communication. Inside this object, an interrupt is called, when new data is received. So I can for example queue this data inside this serial object, but still i need somehow to forward them.
Edit2: A first method that actually works was to implement a timer, which periodically calls an update function. But since the serial rx is interrupt driven, there must be a way for callback, such that I don't need to poll it.

Answer 1

As discussed in the comments, in this use-case it's preferable to not use threading, but exploit the Qt event loop and signal-slot mechanism. Here is the skeleton of the MainWindow and the SerialReciver classes, and how they are wired together in main.cpp. For simplicity, the SerialReceiver class just emits the signal every second with the current time, which will be appended to the editfield's content in the main window.
mainwindow.h:
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QPlainTextEdit>
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow(QWidget *parent = 0);
~MainWindow();
public slots:
void onSerialMessage(const QString &msg);
private:
QPlainTextEdit mTextField;
};
mainwindow.cpp:
#include "mainwindow.h"
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
{
mTextField.setReadOnly(true);
setCentralWidget(&mTextField);
}
MainWindow::~MainWindow()
{
}
void
MainWindow::onSerialMessage(const QString &msg)
{
mTextField.appendPlainText(msg);
}
#endif // MAINWINDOW_H
serialreceiver.h:
#ifndef SERIALRECEIVER_H
#define SERIALRECEIVER_H
#include <QObject>
#include <QTimer>
class SerialReceiver : public QObject
{
Q_OBJECT
public:
explicit SerialReceiver(QObject *parent = nullptr);
signals:
void newMsg(const QString &msg);
public slots:
void onSerialReceived();
private:
QTimer mTimer;
};
#endif // SERIALRECEIVER_H
serialreceiver.cpp:
#include "serialreceiver.h"
#include <QDateTime>
SerialReceiver::SerialReceiver(QObject *parent) : QObject(parent)
{
mTimer.setInterval(1000);
mTimer.setSingleShot(false);
connect(&mTimer, &QTimer::timeout,this,&SerialReceiver::onSerialReceived);
mTimer.start();
}
void
SerialReceiver::onSerialReceived()
{
QDateTime now = QDateTime::currentDateTime();
emit newMsg(now.toString());
}
and main.cpp:
#include "mainwindow.h"
#include "serialreceiver.h"
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
SerialReceiver receiver;
MainWindow w;
QObject::connect(&receiver, &SerialReceiver::newMsg,
&w,&MainWindow::onSerialMessage);
w.show();
return a.exec();
}