Qt - Child widgets are not shown - c++

Question

I'm building a multi-window app and so far creates and shows MainWidget with 8 buttons. My next step is to make each button open a new window which in Qt terms is a child of QWidget. I keep all my buttons and new windows (which should be opened upon a button is clicked) in QVectors. It all compiles with no warnings or errors, however, when I click a button, the corresponding QWidget window is not shown.
mainwidget.h
#ifndef MAINWIDGET_H
#define MAINWIDGET_H
#include <QWidget>
#include <QPushButton>
#include <QGridLayout>
#include <QSignalMapper>
#include "examwindow.h"
namespace Ui { class MainWidget; }
class MainWidget : public QWidget {
Q_OBJECT
public:
explicit MainWidget(QWidget *parent = 0);
~MainWidget();
private:
Ui::MainWidget *ui;
int nExams;
QVector<QString> titles;
QVector<QPushButton*> examButtons;
QGridLayout* mainWidgetLayout;
QVector<ExamWindow*> examWindows;
public slots:
void clickedExamW ();
};
#endif // MAINWIDGET_H
mainwidget.cpp
#include "mainwidget.h"
#include "ui_mainwidget.h"
#include <QDesktopWidget>
#include <iostream>
MainWidget::MainWidget(QWidget *parent) : QWidget(parent), ui(new Ui::MainWidget)
{
ui->setupUi(this);
/**
* #brief Resize the main window size in proportion to the desktop size
*/
double ratio = 0.7;
resize(QDesktopWidget().availableGeometry(this).size() * ratio);
/**
* #brief Set the main window position in the desktop center
*/
QDesktopWidget dw;
int width = this->frameGeometry().width();
int height = this->frameGeometry().height();
int screenWidth = dw.screen() -> width();
int screenHeight = dw.screen() -> height();
this->setGeometry((screenWidth / 2) - (width / 2), (screenHeight / 2) - (height / 2), width, height);
/**
* Set the button titles
*/
titles.push_back("FCE - 2008");
titles.push_back("CAE - 2008");
titles.push_back("CPE - 2008");
titles.push_back("ЕГЭ");
titles.push_back("FCE - 2015");
titles.push_back("CAE - 2015");
titles.push_back("CPE - 2015");
titles.push_back("User's Format");
/**
* Create buttons
*/
nExams = 8; // Number of exams
examButtons.resize(nExams);
for(int i = 0; i < nExams; i++) {
examButtons[i] = new QPushButton(titles[i]);
examButtons[i]->setMinimumSize(QSize(150, 150));
examButtons[i]->setMaximumSize(QSize(500, 500));
examButtons[i]->setObjectName(titles[i]);
connect(examButtons[i], SIGNAL(clicked()), this, SLOT(clickedExamW()));
}
/**
* Add exam buttons to the main widget layout
*/
mainWidgetLayout = new QGridLayout(this);
for(int i = 0; i < nExams; i++)
if (i < nExams / 2)
mainWidgetLayout -> addWidget(examButtons[i], i, 0);
else
mainWidgetLayout -> addWidget(examButtons[i], i - nExams / 2, 1);
/**
* Create exam windows
*/
examWindows.resize(nExams);
for(int i = 0; i < nExams; i++) {
examWindows[i] = new ExamWindow(this);
examWindows[i]->setWindowTitle(titles[i]);
}
}
void MainWidget::clickedExamW() {
QObject *senderObj = sender();
QString senderObjName = senderObj->objectName();
for(int i = 0; i < nExams; i++)
if (senderObjName == titles[i]) {
this->setWindowTitle(titles[i]); // WORKS - it changes the title
examWindows[i]->show(); // DOES NOT WORK - no win shown
}
}
MainWidget::~MainWidget()
{
delete ui;
}
examwindow.h
#ifndef EXAMWINDOW_H
#define EXAMWINDOW_H
#include <QWidget>
class ExamWindow : public QWidget
{
Q_OBJECT
public:
explicit ExamWindow(QWidget *parent = 0);
signals:
public slots:
};
#endif // EXAMWINDOW_H
examwindow.cpp
#include "examwindow.h"
ExamWindow::ExamWindow(QWidget *parent) : QWidget(parent)
{
}

Answer 1

The way, how do you create widgets is ok (examWindows[i] = new ExamWindow(this);). But:
ExamWindow::ExamWindow(QWidget *parent)
: QWidget(parent, Qt::Window)
{}
You need to directly specify a flag that you need a "window" widget.
Or, if you don't want to set parent widget, you may set Qt::WA_DeleteOnClose attribute for automatic releasing memory. Note, that in this case you will have an invalid pointer inside your examWindows vector. It may be resolved if you will use next declaration: QVector<QPointer<ExamWindow>> examWindows;

Answer 2

ANSWER: it turned out that the problem was in this line:
examWindows[i] = new ExamWindow(this);
If I remove 'this', making my windows parentless, it works as intended. I'm puzzled why and I guess I have to delete them now manually.