#pragma once

#include <QtWidgets/QMainWindow>
#include "ui_QtHello.h"

class QtHello : public QMainWindow
{
    Q_OBJECT

public:
    QtHello(QWidget *parent = Q_NULLPTR);

private:
    Ui::QtHelloClass ui;

// add code // Declarative methods
private slots:
    void helloQT();
};

#include "QtHello.h"
#include <QtWidgets/QMessageBox>

QtHello::QtHello(QWidget *parent)
    : QMainWindow(parent)
{
    ui.setupUi(this);

    // add code // Association 3-Elements: Ui-Event-Method
    connect(ui.btnHello, &QPushButton::clicked, this, &QtHello::helloQT);
    // The other way to connect a signal to a slot is to use QObject::connect() and the SIGNAL and SLOT macros. 
    // connect(ui.btnHello, SIGNAL(clicked()), this, SLOT(helloQT()));
}

// add code // Implementation
void QtHello::helloQT()
{
    QMessageBox msgBox;
    msgBox.setText("Hello Qt!");
    msgBox.exec();
}