Adding QButtons to a QTableWidget Header

[SlyPig]

I am trying to add QButtons to the header of a QTableWidget and trying to follow the guidelines here:
qt-support-weekly-27-widgets-on-a-header
qtablewidget-personal-widget-as-header

The code I have works and the buttons appear in the header. The problem is that the buttons don't automatically align to the columns:

If I minimize the window and then display it again, the buttons are aligned, so it seems like some sort of paint/repaint problem. However, I've tried putting 'repaint' just about everywhere and can't find a fix for this. If the window is widened fairly quickly, the same alignment issue happens, but again, a minimize and redisplay fixes it.

Here's the code I'm using. Sorry for putting so much here - this is the smallest I could get it and still show the issue. This forum doesn't allow attachments apparently. Any ideas on how to fix the button / column alignment issue is very much appreciated!

main.cpp:

#include "mainWindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}

mainWindow.h:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QTableWidgetItem>
#include <QPushButton>
#include <QMessageBox>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

const int COL_COUNT = 8;
const int ROW_COUNT = 500;

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

protected:
    void timerEvent(QTimerEvent* event);

private:
    Ui::MainWindow *ui;

    int _timerID; // ID of our timer event
    bool _firstTime;
    
    // List containing pointers to the buttons in the table header
    QList<QPushButton *> _hdrButton;

private slots:
    void popup();
};
#endif // MAINWINDOW_H

mainWindow.cpp:

#include "mainWindow.h"
#include "ui_mainWindow.h"

// Interval on which our timer event fires (in MS)
static const int kMonitorTimerInverval = 1000;

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
    , _timerID(0)
    , _firstTime(true)
{
    ui->setupUi(this);

    ui->tableWidget->setRowCount(ROW_COUNT);
    ui->tableWidget->setColumnCount(COL_COUNT);
    ui->tableWidget->verticalHeader()->setVisible(false);
    ui->tableWidget->horizontalHeader()->setMinimumHeight(40);

    _hdrButton.clear();
    for (int col = 2; col < COL_COUNT; col++) // Columns 3 - 8 only
    {
        _hdrButton.append(new QPushButton);

        connect(_hdrButton[col - 2], SIGNAL(clicked()), this, SLOT(popup()));

        ui->tableWidget->SetHorizontalHeaderItemWidget(col, _hdrButton[col - 2]);
    }

    _timerID = startTimer(kMonitorTimerInverval); // Start the timer
}

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

void MainWindow::popup()
{
    // See which header button was clicked
    int column;
    for (column = 2; column < COL_COUNT; column++)
    {
        if (QObject::sender() == _hdrButton[column - 2])
        {
            break;
        }
    }

    QString msg = QString("Column\n%1").arg(column + 1);
    QMessageBox msgBox;

    msgBox.setWindowTitle("Status");
    msgBox.setText(msg);
    msgBox.setStandardButtons(QMessageBox::Ok);
    msgBox.exec();
}

void MainWindow::timerEvent(QTimerEvent* event)
{
    if ((event->timerId() == _timerID) && _firstTime)
    {
        // No text for columns 3 - 8 since the text will be
        // in the button that's located in the header
        QStringList headerText;
        headerText << "COL 1" << "COL 2" << "" << "" << "" << "" << "" << "";
        ui->tableWidget->setHorizontalHeaderLabels(headerText);

        // Added text to the buttons and configure column sizing
        QString buttonText;
        for (int col = 0; col < COL_COUNT; col++)
        {
            if ((col == 0) || (col == 1)) // First two columns
            {
                ui->tableWidget->resizeColumnToContents(col);
            }
            else // Columns 3 - 8
            {
                buttonText = QString("Button %1").arg(col - 1);
                ui->tableWidget->SetHorizontalHeaderItemText(col, buttonText);
                myHeaderView::Margins buttonMargins = { 4, 4, 4, 4 };
                ui->tableWidget->SetHorizontalHeaderItemMargins(col, buttonMargins);
                ui->tableWidget->SetHorizontalHeaderItemResizeMode(col, QHeaderView::Stretch);
            }
        }
        ui->tableWidget->scrollToBottom();

        _firstTime = false;
    }
}

myTableWidget.h:

#ifndef EU_TABLE_WIDGET_H
#define EU_TABLE_WIDGET_H

#include <QtCore/qglobal.h>
#include <QTableWidget>

#include "myHeaderView.h"

class myTableWidget : public QTableWidget
{
    public:
        myTableWidget(QWidget * parent = Q_NULLPTR);

        void scrollContentsBy(int dx, int dy);
        void SetHorizontalHeaderItemWidget(int column, QWidget * widget);
        void SetHorizontalHeaderItemMargins(int column, myHeaderView::Margins margins);
        void SetHorizontalHeaderItemStylesheet(int column, QString &style);
        void SetHorizontalHeaderItemText(int column, QString &text);
        void SetHorizontalHeaderItemResizeMode(int column, QHeaderView::ResizeMode mode);

    private:
        myHeaderView * mHorizontalHeader;
};
#endif // EU_TABLE_WIDGET_H

myTableWidget.cpp:

#include "myTableWidget.h"

myTableWidget::myTableWidget(QWidget * parent) :
    QTableWidget(parent)
{
    mHorizontalHeader = new myHeaderView(Qt::Orientation::Horizontal, this);
    setHorizontalHeader(mHorizontalHeader);
}

void myTableWidget::scrollContentsBy(int dx, int dy)
{
    QTableWidget::scrollContentsBy(dx, dy);

    if (dx != 0)
        mHorizontalHeader->FixWidgetPositions();
}

void myTableWidget::SetHorizontalHeaderItemWidget(int column, QWidget * widget)
{
    mHorizontalHeader->SetItemWidget(column, widget);
}

void myTableWidget::SetHorizontalHeaderItemMargins(int column, myHeaderView::Margins margins)
{
    mHorizontalHeader->SetItemMargins(column, margins);
}

void myTableWidget::SetHorizontalHeaderItemStylesheet(int column, QString &style)
{
    mHorizontalHeader->SetItemStylesheet(column, style);
}

void myTableWidget::SetHorizontalHeaderItemText(int column, QString &text)
{
    mHorizontalHeader->SetItemText(column, text);
}

void myTableWidget::SetHorizontalHeaderItemResizeMode(int column, QHeaderView::ResizeMode mode)
{
    mHorizontalHeader->setSectionResizeMode(column, mode);
}

myHeaderView.h:

#ifndef MY_HEADER_VIEW_H
#define MY_HEADER_VIEW_H

#include <QWidget>
#include <QHeaderView>
#include <QPushButton>

class myHeaderView : public QHeaderView
{
    public:
        struct Margins
        {
            int left;
            int right;
            int top;
            int buttom;

            Margins(int left = 2, int right = 2, int top = 2, int buttom = 2);
        };

        myHeaderView(Qt::Orientation orientation,
                     QWidget         *parent = nullptr);

        void FixWidgetPositions();
        void SetItemWidget(int index, QWidget * widget);
        void SetItemMargins(int index, Margins margins);
        void SetItemStylesheet(int index, QString &style);
        void SetItemText(int index, QString &text);
        void SetItemResizeMode(int index, QHeaderView::ResizeMode mode);

    private:
        struct Item
        {
            QWidget * item;
            Margins margins;

            Item();
        };

        QMap<int, Item> mItems;

        void showEvent(QShowEvent * e);
        void HandleSectionResized(int i);
        void HandleSectionMoved(int logical, int oldVisualIndex, int newVisualIndex);
};
#endif // MY_HEADER_VIEW_H

myHeaderView.cpp:

#include "myHeaderView.h"

myHeaderView::myHeaderView(Qt::Orientation orientation, QWidget * parent) :
    QHeaderView(orientation, parent)
{
    connect(this, &myHeaderView::sectionResized, this, &myHeaderView::HandleSectionResized);
    connect(this, &myHeaderView::sectionMoved,   this, &myHeaderView::HandleSectionMoved);
}


void myHeaderView::showEvent(QShowEvent *e)
{
    for (int i = 0; i < count(); i++)
    {
        if (!mItems[i].item)
        {
            mItems[i].item = new QWidget(this);
        }
        else
        {
            mItems[i].item->setParent(this);
        }

        mItems[i].item->setGeometry(sectionViewportPosition(i) + mItems[i].margins.left,
                                    mItems[i].margins.top,
                                    sectionSize(i) - mItems[i].margins.left - mItems[i].margins.right - 1,
                                    height() - mItems[i].margins.top - mItems[i].margins.buttom - 1);
        mItems[i].item->show();
    }

    QHeaderView::showEvent(e);
}


void myHeaderView::HandleSectionResized(int i)
{
    for (int j = visualIndex(i); j < count(); j++)
    {
        int logical = logicalIndex(j);
        mItems[logical].item->setGeometry(sectionViewportPosition(logical) + mItems[i].margins.left,
                                          mItems[i].margins.top,
                                          sectionSize(logical) - mItems[i].margins.left - mItems[i].margins.right - 1,
                                          height() - mItems[i].margins.top - mItems[i].margins.buttom - 1);
    }
}


void myHeaderView::HandleSectionMoved(int logical, int oldVisualIndex, int newVisualIndex)
{
    for (int i = qMin(oldVisualIndex, newVisualIndex); i < count(); i++)
    {
        logical = logicalIndex(i);
        mItems[logical].item->setGeometry(sectionViewportPosition(logical) + mItems[i].margins.left,
                                          mItems[i].margins.top,
                                          sectionSize(logical) - mItems[i].margins.left - mItems[i].margins.right - 1,
                                          height() - mItems[i].margins.top - mItems[i].margins.buttom - 1);
    }
}


void myHeaderView::FixWidgetPositions()
{
    for (int i = 0; i < count(); i++)
    {
        mItems[i].item->setGeometry(sectionViewportPosition(i) + mItems[i].margins.left,
                                    mItems[i].margins.top,
                                    sectionSize(i) - mItems[i].margins.left - mItems[i].margins.right - 1,
                                    height() - mItems[i].margins.top - mItems[i].margins.buttom - 1);
    }
}


void myHeaderView::SetItemWidget(int index, QWidget * widget)
{
    widget->setParent(this);
    mItems[index].item = widget;
}


void myHeaderView::SetItemMargins(int index, myHeaderView::Margins margins)
{
    mItems[index].margins = margins;

    HandleSectionResized(index);
}

void myHeaderView::SetItemStylesheet(int index, QString &style)
{
    mItems[index].item->setStyleSheet(style);
}

void myHeaderView::SetItemText(int index, QString &text)
{
    reinterpret_cast<QPushButton *>(mItems[index].item)->setText(text);
}

void myHeaderView::SetItemResizeMode(int index, QHeaderView::ResizeMode mode)
{
    reinterpret_cast<QHeaderView *>(mItems[index].item)->setSectionResizeMode(mode);
}

myHeaderView::Margins::Margins(int left, int right, int top, int buttom) :
    left(left),
    right(right),
    top(top),
    buttom(buttom)
{
}

myHeaderView::Item::Item() :
    item(nullptr)
{
}