How to manage mainwindow from QThread in Qt - c++

Question

My problem is the following one: I have 2 classes (mainwindow and mythread), I run the thread from the mainwindow and I would like to display some QLabel of my mainwindow from mythread :
mythread.cpp :
void mythread::run()
{
while(1)
{
this->read();
}
}
void mythread::read()
{
RF_Power_Control(&MonLecteur, TRUE, 0);
status = ISO14443_3_A_PollCard(&MonLecteur, atq, sak, uid, &uid_len);
if (status != 0){
//display Qlabel in mainwindow
}
}
mainwindow.cpp :
_thread = new mythread();
_thread->start();

Answer 1

You should use Qt's signal/slot mechanism. The thread will emit a signal, that new data has been read. Any interested object can connect to that signal, and perform actions depending on it.
This also works across thread-boundaries, as in your example. In Qt, it is required that only the main-thread interacts with UI elements.
Here is an outline:
// Your mainwindow:
class MyWindow : public QMainWindow {
Q_OBJECT
// as needed
private slots:
void setLabel(const QString &t) { m_label->setText(t); }
};
// Your thread
class MyThread: public QThread {
Q_OBJECT
// as needed
signals:
void statusUpdated(const QString &t);
};
// in your loop
if (status != 0) {
emit statusUpdated("New Status!");
}
// in your mainwindow
_thread = new MyThread;
connect(_thread, &MyThread::statusUpdated, this, &MyWindow::setLabel);
_thread->start();