Add menubar to QDialog or convert QDialog to QMainWindow ?

I made my program and declared it(the c++ file I am executing in the main c++ file) as a class public QDialog like this

Code:

---

#include <QDialog>
class DateListDialog: public QDialog {
Q_OBJECT
public:DateListDialog();
}

---

but I want to add a menubar and I am not sure how if it is a QDialog so I wish to turn the QDialog into a QMainWindow I tried changing the code on the header to:

Code:

---

#include <QMainWindow>
class DateListDialog: public QMainWindow {
Q_OBJECT
public:DateListDialog();
}

---

but then when I do that and add the menubar all it shows it the menubar and not all the other gui items so basically its just an empty QMainWindow

the code I used to add the gui items is this:

Code:

---

#include <QtGui>
#include "datelistdialog.h"
#include "listwidgetdialog.h"
#include <sstream>
#include <iostream>
using namespace std;
 
DateListDialog::DateListDialog()
{
 
    QStringList dates, foods, totalCalories, totalProteins, totalCarbs, totalFats, totalSugars, totalSodiums, totalFibers;
    QStringList labels;
    labels << tr("Dates") << tr("Foods") << tr("Total Calories") << tr("Total Proteins") << tr("Total Carbs") << tr("Total Fats") << tr("Total Sugars") << tr("Total Sodiums") << tr("Total Fibers");
 
    treeWidget = new QTreeWidget;
    treeWidget->setColumnCount(9);
    treeWidget->setHeaderLabels(labels);
 
 
    QVBoxLayout *mainLayout = new QVBoxLayout;
    mainLayout->addWidget(treeWidget);
    setLayout(mainLayout);
 
 
        QFile file(QDir::homePath() + "/caloriecounter.txt");
        if (file.open(QIODevice::ReadOnly)){
            QTextStream input(&file);
            input.setCodec("UTF-8");
            while(!input.atEnd()){
                //dates << input.readLine();
                foods << input.readLine();
                totalCalories << input.readLine();
                totalProteins << input.readLine();
                totalCarbs << input.readLine();
                totalFats << input.readLine();
                totalSugars << input.readLine();
                totalSodiums << input.readLine();
                totalFibers << input.readLine();
                input.readLine();
            }
        }
 
 
    for (int i = 0; i < foods.size(); ++i) {
        QTreeWidgetItem* item = new QTreeWidgetItem;
        //item->setText(0, dates[i]);
        item->setText(1, foods[i]);
        item->setText(2, totalCalories[i]);
        item->setText(3, totalProteins[i]);
        item->setText(4, totalCarbs[i]);
        item->setText(5, totalFats[i]);
        item->setText(6, totalSugars[i]);
        item->setText(7,totalSodiums[i]);
        item->setText(8, totalFibers[i]);
        treeWidget->addTopLevelItem(item);
 
    }
    //createActions();
    //createMenus();
}

---

Any suggestions would be greatly appreciated.
Thanks!

EDIT::: I think I figured a way how to do it but I will need a little bit of help with it I cannot find anything on the internet on how to do it.
What I think will work is to set the QDialog from the datelistdialog.cpp file as the main widget of another file called MainWindow which is a mainwindow
I tried doing this for the header:

Code:

---

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
class MainWindow : public QMainWindow
{
 
public:
    MainWindow();
};
 
#endif // MAINWINDOW_H

---

and this for the c++ file:

Code:

---

#include "mainwindow.h"
#include "datelistdialog.h"
 
MainWindow::MainWindow()
{
    DateListDialog w;
    setCentralWidget(w);
}

---

unfortunately it did not work =/
so I tried this for the c++

Code:

---

#include "mainwindow.h"
#include "datelistdialog.h"
 
MainWindow::MainWindow()
{
    DateListDialog w;
    w.exec();
}

---

it opens the QDialog but it does not set it as the centralWidget of the MainWindow tho =/

EDIT!:!:!:!:!:!:
The reason it was not working for me was after i turned it to a MainWindow I forgot the "setCentralWidget" because you do not need that on QDialogs.