PushButton is opened in different window - c++

Question

i am new at QT
i created a window and i want to add a button on this window but the button is opened in different window.
How to add this button to default window
Here is my code;
mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "QPushButton"
#include "QDesktopWidget"
#include <iostream>
using namespace std;
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
QPushButton* buton1 = new QPushButton("Hello");
buton1 -> setGeometry(QRect(QPoint(100,100),QSize(200,50)));
connect(buton1, &QPushButton::released, this, &MainWindow::buton_fonk);
buton1 -> show();
ui->setupUi(this);
}
void MainWindow::buton_fonk()
{
cout << "here" << endl;
}
MainWindow::~MainWindow()
{
delete ui;
}
main.cpp
#include "mainwindow.h"
#include <QApplication>
#include <QDesktopWidget>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.setWindowState(Qt::WindowMaximized);
w.showFullScreen();
return a.exec();
}

Answer 1

You need to make QPushButton a child of the main window for it to be rendered inside the main window, otherwise QPushButton will be an independent widget.
Usually all Qt Widgets accept a pointer to parent widget, QPushButton also accept a pointer to parent widtet.
QPushButton(const QString &text, QWidget *parent = nullptr)
To make QPushButton child of MainWindow, add this as second parameter to QPushButotn constructor.
QPushButton* buton1 = new QPushButton("Hello", this); // Make MainWindow as parent of QPushButton
Ideally you should create a layout and add all your widgets to this layout and then set the central widget of MainWindow to this layout.
QVBoxLayout *mainLayout = new QVBoxLayout;
mainLayout->addWidget(button1);
// Add anyother widget to your layout
this->setCentralWidget(mainLayout);
Hope this helps.