QScrollArea and QVBoxLayout issues with dynamically added widgets - qt

Question

Im running into a weird issue with dynamically added widgets to a QVBoxLayout contained inside a QScrollArea. If I add the widgets it works as expected, however after all widgets are removed, there are still some artifacts on the screen. See screenshot bellow:
See the code bellow:
ui_mainwindow.h
/********************************************************************************
** Form generated from reading UI file 'mainwindow.ui'
**
** Created by: Qt User Interface Compiler version 5.2.0
**
** WARNING! All changes made in this file will be lost when recompiling UI file!
********************************************************************************/
#ifndef UI_MAINWINDOW_H
#define UI_MAINWINDOW_H
#include <QtCore/QVariant>
#include <QtWidgets/QAction>
#include <QtWidgets/QApplication>
#include <QtWidgets/QButtonGroup>
#include <QtWidgets/QHBoxLayout>
#include <QtWidgets/QHeaderView>
#include <QtWidgets/QMainWindow>
#include <QtWidgets/QMenuBar>
#include <QtWidgets/QPushButton>
#include <QtWidgets/QScrollArea>
#include <QtWidgets/QStatusBar>
#include <QtWidgets/QToolBar>
#include <QtWidgets/QVBoxLayout>
#include <QtWidgets/QWidget>
QT_BEGIN_NAMESPACE
class Ui_MainWindow
{
public:
QWidget *centralWidget;
QVBoxLayout *verticalLayout_2;
QScrollArea *scrollArea;
QWidget *scrollAreaWidgetContents;
QHBoxLayout *horizontalLayout_2;
QVBoxLayout *verticalLayout;
QPushButton *pushButton;
QPushButton *pushButton_2;
QMenuBar *menuBar;
QToolBar *mainToolBar;
QStatusBar *statusBar;
void setupUi(QMainWindow *MainWindow)
{
if (MainWindow->objectName().isEmpty())
MainWindow->setObjectName(QStringLiteral("MainWindow"));
MainWindow->resize(600, 396);
centralWidget = new QWidget(MainWindow);
centralWidget->setObjectName(QStringLiteral("centralWidget"));
verticalLayout_2 = new QVBoxLayout(centralWidget);
verticalLayout_2->setSpacing(6);
verticalLayout_2->setContentsMargins(11, 11, 11, 11);
verticalLayout_2->setObjectName(QStringLiteral("verticalLayout_2"));
scrollArea = new QScrollArea(centralWidget);
scrollArea->setObjectName(QStringLiteral("scrollArea"));
scrollArea->setWidgetResizable(true);
scrollAreaWidgetContents = new QWidget();
scrollAreaWidgetContents->setObjectName(QStringLiteral("scrollAreaWidgetContents"));
scrollAreaWidgetContents->setGeometry(QRect(0, 0, 574, 246));
horizontalLayout_2 = new QHBoxLayout(scrollAreaWidgetContents);
horizontalLayout_2->setSpacing(6);
horizontalLayout_2->setContentsMargins(11, 11, 11, 11);
horizontalLayout_2->setObjectName(QStringLiteral("horizontalLayout_2"));
verticalLayout = new QVBoxLayout();
verticalLayout->setSpacing(6);
verticalLayout->setObjectName(QStringLiteral("verticalLayout"));
horizontalLayout_2->addLayout(verticalLayout);
scrollArea->setWidget(scrollAreaWidgetContents);
verticalLayout_2->addWidget(scrollArea);
pushButton = new QPushButton(centralWidget);
pushButton->setObjectName(QStringLiteral("pushButton"));
verticalLayout_2->addWidget(pushButton);
pushButton_2 = new QPushButton(centralWidget);
pushButton_2->setObjectName(QStringLiteral("pushButton_2"));
verticalLayout_2->addWidget(pushButton_2);
MainWindow->setCentralWidget(centralWidget);
menuBar = new QMenuBar(MainWindow);
menuBar->setObjectName(QStringLiteral("menuBar"));
menuBar->setGeometry(QRect(0, 0, 600, 22));
MainWindow->setMenuBar(menuBar);
mainToolBar = new QToolBar(MainWindow);
mainToolBar->setObjectName(QStringLiteral("mainToolBar"));
MainWindow->addToolBar(Qt::TopToolBarArea, mainToolBar);
statusBar = new QStatusBar(MainWindow);
statusBar->setObjectName(QStringLiteral("statusBar"));
MainWindow->setStatusBar(statusBar);
retranslateUi(MainWindow);
QMetaObject::connectSlotsByName(MainWindow);
} // setupUi
void retranslateUi(QMainWindow *MainWindow)
{
MainWindow->setWindowTitle(QApplication::translate("MainWindow", "MainWindow", 0));
pushButton->setText(QApplication::translate("MainWindow", "add one", 0));
pushButton_2->setText(QApplication::translate("MainWindow", "remove one", 0));
} // retranslateUi
};
namespace Ui {
class MainWindow: public Ui_MainWindow {};
} // namespace Ui
QT_END_NAMESPACE
#endif // UI_MAINWINDOW_H
mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
private slots:
void on_pushButton_clicked();
void on_pushButton_2_clicked();
private:
Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H
mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QLabel>
#include <QDebug>
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::on_pushButton_clicked()
{
ui->verticalLayout->addWidget(new QLabel("This is a label", this));
qDebug() << "Labels count: " << ui->verticalLayout->count();
}
void MainWindow::on_pushButton_2_clicked()
{
delete ui->verticalLayout->takeAt(0);
qDebug() << "Labels count: " << ui->verticalLayout->count();
}
main.cpp
#include "mainwindow.h"
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}

Answer 1

It seems like I also have to remove the QLayoutItem AND the Widget, just removing the widget or the QLayoutItem (which I did try) doesn't work, both have to be removed, like so:
QLayoutItem *child = ui->verticalLayout->takeAt(0);
if (child)
{
delete child->widget();
delete child;
}