How to access ui qT elements?

Question

Qt

Such a problem:
I create a QT project in the studio, I add a GUI class. In the designer I make one button pushButton
.hpp

#pragma once
#ifndef MAINWINDOW_HPP
#define MAINWINDOW_HPP
#include <QMainWindow>
namespace Ui {class MainWindow;}

class MainWindow : public QMainWindow {
  Q_OBJECT

public:
  MainWindow(QWidget * parent = Q_NULLPTR);
  ~MainWindow();
  
public:
  Ui::MainWindow *ui;
};

#endif // MAINWINDOW_HPP

.cpp

#include "mainwindow.hpp"
#include "ui_mainwindow.h"

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

MainWindow::~MainWindow() {
  delete ui;
}

The whole drama lies in the lack of ui elements in mainwindow.cpp.
When I start typing ui-> I get only a list instead of elements: setupUi
I can't do anything with pushButton in mainwindow.cpp.
But! When I create an empty project directly in QtCreator and add a button to the form, I get access to everything I need using the ui-> method.
Why is it different in studio with qt addon? why can't I access the button on the form from the studio code editor? why does the same in QT work ok?

Answer 1

try to build the project after adding the elements.