Cannot Access the Qt UI from an external cpp file - c++

Question

Im trying to make a program an in that program I want to press a button that processes some text in another cpp file and appends my QTextEdit. I basically as a test just setup my button to run a function in the other file and also in when the program starts. When it starts it properly prints to the Text Edit as well as my console but when I press my button it only prints to the console and not to my TextEdit. For the function that appends the text in my TextEdit and prints to the console, I made it a public slot so I could access it from my other file.
This is my quiz.cpp
#include <iostream>
#include "quiz.h"
#include "ui_quiz.h"
#include "test.h"
Quiz::Quiz(QWidget *parent) : QMainWindow(parent), ui(new Ui::Quiz) {
ui->setupUi(this);
setText();
}
Quiz::~Quiz() {
delete ui;
}
void Quiz::on_actionQuit_triggered() {
QCoreApplication::quit();
}
void Quiz::on_pushButton_clicked() {
run();
}
void Quiz::setText() {
ui->console->append("Hello");
std::cout << "Hello world!" << std::endl;
}
This is its header:
#ifndef QUIZ_H
#define QUIZ_H
#include <QMainWindow>
namespace Ui {
class Quiz;
}
class Quiz : public QMainWindow
{
Q_OBJECT
public:
explicit Quiz(QWidget *parent = 0);
~Quiz();
public slots:
void setText();
private slots:
void on_actionQuit_triggered();
void on_pushButton_clicked();
private:
Ui::Quiz *ui;
};
#endif // QUIZ_H
This is my test.cpp:
#include "quiz.h"
#include "test.h"
#include "ui_quiz.h"
void run() {
Quiz* quiz = new Quiz();
quiz->setText();
}
and its header:
#ifndef TEST_H
#define TEST_H
#endif // TEST_H
void run();
What am I doing wrong? Why can I not access the ui but the rest of the function runs?

Answer 1

you can access UI only from Main thread.
you can use signal-slot to do that.
write your slot in main. and emit your signal from second class.
connect signal-slot in constructor main.
second class .h file:
void updateUI(QString str);
second class .cpp file:
emit updateUI("some text");
main class .h file:
void updateUI(QString str);
main class .cpp file(implementation):
void Main::updateUI(QString str)
{
// change ui here
}
main class .cpp file (in constructor):
connect(secondobj, &secondclass::updateUI, this, &mainclass::updateUI);

Answer 2

In header file of your cpp where you want to use the UI, add the following lines of ui.
##.h file:
class A
{
Public:
Ui::MainWindow *ui;
}
##.cpp file:
ui->label->setText(ui->button->text());