Cleanup QtWidgets (tools) examples

Cleanup QtWidgets tools examples:
 - use member-init (clang-tidy)
 - fix includes/don't include QtWidgets globally
 - include own header first
 - use nullptr (clang-tidy)
 - avoid c-style casts
 - use QVector instead QList
 - use QItemDelegate instead QStyledItemDelegate

Change-Id: Ibe9440cdf711e5cc2138c054864edebe1fc95731
Reviewed-by: Paul Wicking <paul.wicking@qt.io>

60 files changed, 426 insertions, 376 deletions

diff --git a/examples/widgets/tools/codecs/mainwindow.cpp b/examples/widgets/tools/codecs/mainwindow.cpp
index 53db9fe61f..6b601062b6 100644
--- a/examples/widgets/tools/codecs/mainwindow.cpp
+++ b/examples/widgets/tools/codecs/mainwindow.cpp
@@ -48,12 +48,21 @@
 **
 ****************************************************************************/
 
-#include <QtWidgets>
-
 #include "mainwindow.h"
 #include "encodingdialog.h"
 #include "previewform.h"
 
+#include <QAction>
+#include <QApplication>
+#include <QDesktopWidget>
+#include <QFileDialog>
+#include <QMenuBar>
+#include <QMessageBox>
+#include <QPlainTextEdit>
+#include <QRegularExpression>
+#include <QTextCodec>
+#include <QTextStream>
+
 MainWindow::MainWindow()
 {
     textEdit = new QPlainTextEdit;
@@ -146,14 +155,14 @@ void MainWindow::findCodecs()
         QTextCodec *codec = QTextCodec::codecForMib(mib);
 
         QString sortKey = codec->name().toUpper();
-        int rank;
+        char rank;
 
         if (sortKey.startsWith(QLatin1String("UTF-8"))) {
             rank = 1;
         } else if (sortKey.startsWith(QLatin1String("UTF-16"))) {
             rank = 2;
         } else if ((match = iso8859RegExp.match(sortKey)).hasMatch()) {
-            if (match.captured(1).size() == 1)
+            if (match.capturedRef(1).size() == 1)
                 rank = 3;
             else
                 rank = 4;
@@ -164,7 +173,8 @@ void MainWindow::findCodecs()
 
         codecMap.insert(sortKey, codec);
     }
-    codecs = codecMap.values();
+    for (const auto &codec : qAsConst(codecMap))
+      codecs += codec;
 }
 
 void MainWindow::createMenus()
diff --git a/examples/widgets/tools/codecs/mainwindow.h b/examples/widgets/tools/codecs/mainwindow.h
index 64494d1960..cf18222520 100644
--- a/examples/widgets/tools/codecs/mainwindow.h
+++ b/examples/widgets/tools/codecs/mainwindow.h
@@ -51,7 +51,7 @@
 #ifndef MAINWINDOW_H
 #define MAINWINDOW_H
 
-#include <QList>
+#include <QVector>
 #include <QMainWindow>
 
 QT_BEGIN_NAMESPACE
@@ -81,10 +81,10 @@ private:
     void findCodecs();
     void createMenus();
 
-    QList<QAction *> saveAsActs;
+    QVector<QAction *> saveAsActs;
     QPlainTextEdit *textEdit;
     PreviewForm *previewForm;
-    QList<QTextCodec *> codecs;
+    QVector<QTextCodec *> codecs;
     EncodingDialog *m_encodingDialog = nullptr;
 };
 
diff --git a/examples/widgets/tools/codecs/previewform.cpp b/examples/widgets/tools/codecs/previewform.cpp
index 206b5757cd..ec75ebb9fa 100644
--- a/examples/widgets/tools/codecs/previewform.cpp
+++ b/examples/widgets/tools/codecs/previewform.cpp
@@ -48,10 +48,19 @@
 **
 ****************************************************************************/
 
-#include <QtWidgets>
-
 #include "previewform.h"
 
+#include <QApplication>
+#include <QComboBox>
+#include <QDesktopWidget>
+#include <QDialogButtonBox>
+#include <QGridLayout>
+#include <QLabel>
+#include <QPlainTextEdit>
+#include <QPushButton>
+#include <QTextCodec>
+#include <QTextStream>
+
 // Helpers for creating hex dumps
 static void indent(QTextStream &str, int indent)
 {
@@ -83,8 +92,7 @@ static void formatHex(QTextStream &str, const QByteArray &data)
 
 static void formatPrintableCharacters(QTextStream &str, const QByteArray &data)
 {
-    for (int i = 0, size = data.size(); i < size; ++i) {
-        const char c = data.at(i);
+    for (const char c : data) {
         switch (c) {
         case '\0':
             str << "\\0";
@@ -179,7 +187,7 @@ PreviewForm::PreviewForm(QWidget *parent)
     resize(screenGeometry.width() * 2 / 5, screenGeometry.height() / 2);
 }
 
-void PreviewForm::setCodecList(const QList<QTextCodec *> &list)
+void PreviewForm::setCodecList(const QVector<QTextCodec *> &list)
 {
     encodingComboBox->clear();
     for (const QTextCodec *codec : list) {
@@ -226,10 +234,10 @@ void PreviewForm::updateTextEdit()
         statusLabel->setText(message);
         statusLabel->setStyleSheet(QStringLiteral("background-color: \"red\";"));
     } else if (state.invalidChars) {
-        statusLabel->setText(tr("%1: %n invalid characters", 0, state.invalidChars).arg(name));
+        statusLabel->setText(tr("%1: %n invalid characters", nullptr, state.invalidChars).arg(name));
         statusLabel->setStyleSheet(QStringLiteral("background-color: \"yellow\";"));
     } else {
-        statusLabel->setText(tr("%1: %n bytes converted", 0, encodedData.size()).arg(name));
+        statusLabel->setText(tr("%1: %n bytes converted", nullptr, encodedData.size()).arg(name));
         statusLabel->setStyleSheet(QString());
     }
     if (success)
diff --git a/examples/widgets/tools/codecs/previewform.h b/examples/widgets/tools/codecs/previewform.h
index 6335b6539f..02eb3533f3 100644
--- a/examples/widgets/tools/codecs/previewform.h
+++ b/examples/widgets/tools/codecs/previewform.h
@@ -52,7 +52,7 @@
 #define PREVIEWFORM_H
 
 #include <QDialog>
-#include <QList>
+#include <QVector>
 
 QT_BEGIN_NAMESPACE
 class QComboBox;
@@ -71,7 +71,7 @@ class PreviewForm : public QDialog
 public:
     explicit PreviewForm(QWidget *parent = nullptr);
 
-    void setCodecList(const QList<QTextCodec *> &list);
+    void setCodecList(const QVector<QTextCodec *> &list);
     void setEncodedData(const QByteArray &data);
     QString decodedString() const { return decodedStr; }
 
diff --git a/examples/widgets/tools/completer/fsmodel.h b/examples/widgets/tools/completer/fsmodel.h
index 7b2e7b7dab..587e08b192 100644
--- a/examples/widgets/tools/completer/fsmodel.h
+++ b/examples/widgets/tools/completer/fsmodel.h
@@ -62,7 +62,7 @@
 class FileSystemModel : public QFileSystemModel
 {
 public:
-    FileSystemModel(QObject *parent = 0);
+    FileSystemModel(QObject *parent = nullptr);
     QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override;
 };
 //! [0]
diff --git a/examples/widgets/tools/completer/mainwindow.cpp b/examples/widgets/tools/completer/mainwindow.cpp
index 114ff0fd7c..b50e0a5456 100644
--- a/examples/widgets/tools/completer/mainwindow.cpp
+++ b/examples/widgets/tools/completer/mainwindow.cpp
@@ -48,13 +48,28 @@
 **
 ****************************************************************************/
 
-#include <QtWidgets>
-#include "fsmodel.h"
 #include "mainwindow.h"
+#include "fsmodel.h"
+
+#include <QAction>
+#include <QApplication>
+#include <QCheckBox>
+#include <QComboBox>
+#include <QCompleter>
+#include <QGridLayout>
+#include <QHeaderView>
+#include <QLabel>
+#include <QLineEdit>
+#include <QMenuBar>
+#include <QMessageBox>
+#include <QSpinBox>
+#include <QStandardItemModel>
+#include <QStringListModel>
+#include <QTreeView>
 
 //! [0]
 MainWindow::MainWindow(QWidget *parent)
-    : QMainWindow(parent), completer(0), lineEdit(0)
+    : QMainWindow(parent)
 {
     createMenu();
 
@@ -64,8 +79,8 @@ MainWindow::MainWindow(QWidget *parent)
     modelLabel->setText(tr("Model"));
 
     modelCombo = new QComboBox;
-    modelCombo->addItem(tr("QFileSytemModel"));
-    modelCombo->addItem(tr("QFileSytemModel that shows full path"));
+    modelCombo->addItem(tr("QFileSystemModel"));
+    modelCombo->addItem(tr("QFileSystemModel that shows full path"));
     modelCombo->addItem(tr("Country list"));
     modelCombo->addItem(tr("Word list"));
     modelCombo->setCurrentIndex(0);
@@ -144,17 +159,17 @@ void MainWindow::createMenu()
     connect(aboutAct, &QAction::triggered, this, &MainWindow::about);
     connect(aboutQtAct, &QAction::triggered, qApp, &QApplication::aboutQt);
 
-    QMenu* fileMenu = menuBar()->addMenu(tr("File"));
+    QMenu *fileMenu = menuBar()->addMenu(tr("File"));
     fileMenu->addAction(exitAction);
 
-    QMenu* helpMenu = menuBar()->addMenu(tr("About"));
+    QMenu *helpMenu = menuBar()->addMenu(tr("About"));
     helpMenu->addAction(aboutAct);
     helpMenu->addAction(aboutQtAct);
 }
 //! [4]
 
 //! [5]
-QAbstractItemModel *MainWindow::modelFromFile(const QString& fileName)
+QAbstractItemModel *MainWindow::modelFromFile(const QString &fileName)
 {
     QFile file(fileName);
     if (!file.open(QFile::ReadOnly))
@@ -170,7 +185,7 @@ QAbstractItemModel *MainWindow::modelFromFile(const QString& fileName)
     while (!file.atEnd()) {
         QByteArray line = file.readLine();
         if (!line.isEmpty())
-            words << line.trimmed();
+            words << QString::fromUtf8(line.trimmed());
     }
 
 #ifndef QT_NO_CURSOR
@@ -191,8 +206,8 @@ QAbstractItemModel *MainWindow::modelFromFile(const QString& fileName)
     for (int i = 0; i < words.count(); ++i) {
         QModelIndex countryIdx = m->index(i, 0);
         QModelIndex symbolIdx = m->index(i, 1);
-        QString country = words[i].mid(0, words[i].length() - 2).trimmed();
-        QString symbol = words[i].right(2);
+        QString country = words.at(i).mid(0, words[i].length() - 2).trimmed();
+        QString symbol = words.at(i).right(2);
         m->setData(countryIdx, country);
         m->setData(symbolIdx, symbol);
     }
@@ -233,7 +248,7 @@ void MainWindow::changeModel()
     case 0:
         { // Unsorted QFileSystemModel
             QFileSystemModel *fsModel = new QFileSystemModel(completer);
-            fsModel->setRootPath("");
+            fsModel->setRootPath(QString());
             completer->setModel(fsModel);
             contentsLabel->setText(tr("Enter file path"));
         }
@@ -243,7 +258,7 @@ void MainWindow::changeModel()
         {   // FileSystemModel that shows full paths
             FileSystemModel *fsModel = new FileSystemModel(completer);
             completer->setModel(fsModel);
-            fsModel->setRootPath("");
+            fsModel->setRootPath(QString());
             contentsLabel->setText(tr("Enter file path"));
         }
         break;
diff --git a/examples/widgets/tools/completer/mainwindow.h b/examples/widgets/tools/completer/mainwindow.h
index 2bb351ec47..6e6238bf32 100644
--- a/examples/widgets/tools/completer/mainwindow.h
+++ b/examples/widgets/tools/completer/mainwindow.h
@@ -59,7 +59,6 @@ class QComboBox;
 class QCompleter;
 class QLabel;
 class QLineEdit;
-class QProgressBar;
 class QCheckBox;
 class QSpinBox;
 QT_END_NAMESPACE
@@ -70,7 +69,7 @@ class MainWindow : public QMainWindow
     Q_OBJECT
 
 public:
-    MainWindow(QWidget *parent = 0);
+    MainWindow(QWidget *parent = nullptr);
 
 private slots:
     void about();
@@ -83,16 +82,16 @@ private slots:
 //! [1]
 private:
     void createMenu();
-    QAbstractItemModel *modelFromFile(const QString& fileName);
+    QAbstractItemModel *modelFromFile(const QString &fileName);
 
-    QComboBox *caseCombo;
-    QComboBox *modeCombo;
-    QComboBox *modelCombo;
-    QSpinBox *maxVisibleSpinBox;
-    QCheckBox *wrapCheckBox;
-    QCompleter *completer;
-    QLabel *contentsLabel;
-    QLineEdit *lineEdit;
+    QComboBox *caseCombo = nullptr;
+    QComboBox *modeCombo = nullptr;
+    QComboBox *modelCombo = nullptr;
+    QSpinBox *maxVisibleSpinBox = nullptr;
+    QCheckBox *wrapCheckBox = nullptr;
+    QCompleter *completer = nullptr;
+    QLabel *contentsLabel = nullptr;
+    QLineEdit *lineEdit = nullptr;
 };
 //! [1]
 
diff --git a/examples/widgets/tools/customcompleter/mainwindow.cpp b/examples/widgets/tools/customcompleter/mainwindow.cpp
index 39f5f39617..b8072b505c 100644
--- a/examples/widgets/tools/customcompleter/mainwindow.cpp
+++ b/examples/widgets/tools/customcompleter/mainwindow.cpp
@@ -48,13 +48,20 @@
 **
 ****************************************************************************/
 
-#include <QtWidgets>
 #include "mainwindow.h"
 #include "textedit.h"
 
+#include <QAction>
+#include <QApplication>
+#include <QCompleter>
+#include <QFile>
+#include <QMenuBar>
+#include <QMessageBox>
+#include <QStringListModel>
+
 //! [0]
 MainWindow::MainWindow(QWidget *parent)
-    : QMainWindow(parent), completer(0)
+    : QMainWindow(parent)
 {
     createMenu();
 
@@ -83,10 +90,10 @@ void MainWindow::createMenu()
     connect(aboutAct, &QAction::triggered, this, &MainWindow::about);
     connect(aboutQtAct, &QAction::triggered, qApp, &QApplication::aboutQt);
 
-    QMenu* fileMenu = menuBar()->addMenu(tr("File"));
+    QMenu *fileMenu = menuBar()->addMenu(tr("File"));
     fileMenu->addAction(exitAction);
 
-    QMenu* helpMenu = menuBar()->addMenu(tr("About"));
+    QMenu *helpMenu = menuBar()->addMenu(tr("About"));
     helpMenu->addAction(aboutAct);
     helpMenu->addAction(aboutQtAct);
 }
@@ -107,7 +114,7 @@ QAbstractItemModel *MainWindow::modelFromFile(const QString& fileName)
     while (!file.atEnd()) {
         QByteArray line = file.readLine();
         if (!line.isEmpty())
-            words << line.trimmed();
+            words << QString::fromUtf8(line.trimmed());
     }
 
 #ifndef QT_NO_CURSOR
diff --git a/examples/widgets/tools/customcompleter/mainwindow.h b/examples/widgets/tools/customcompleter/mainwindow.h
index 436377cce7..cde553e291 100644
--- a/examples/widgets/tools/customcompleter/mainwindow.h
+++ b/examples/widgets/tools/customcompleter/mainwindow.h
@@ -55,11 +55,7 @@
 
 QT_BEGIN_NAMESPACE
 class QAbstractItemModel;
-class QComboBox;
 class QCompleter;
-class QLabel;
-class QLineEdit;
-class QProgressBar;
 QT_END_NAMESPACE
 class TextEdit;
 
@@ -69,7 +65,7 @@ class MainWindow : public QMainWindow
     Q_OBJECT
 
 public:
-    MainWindow(QWidget *parent = 0);
+    MainWindow(QWidget *parent = nullptr);
 
 private slots:
     void about();
@@ -78,7 +74,7 @@ private:
     void createMenu();
     QAbstractItemModel *modelFromFile(const QString& fileName);
 
-    QCompleter *completer;
+    QCompleter *completer = nullptr;
     TextEdit *completingTextEdit;
 };
 //! [0]
diff --git a/examples/widgets/tools/customcompleter/textedit.cpp b/examples/widgets/tools/customcompleter/textedit.cpp
index d42f7b38bb..0d536fea3c 100644
--- a/examples/widgets/tools/customcompleter/textedit.cpp
+++ b/examples/widgets/tools/customcompleter/textedit.cpp
@@ -60,7 +60,7 @@
 
 //! [0]
 TextEdit::TextEdit(QWidget *parent)
-: QTextEdit(parent), c(0)
+    : QTextEdit(parent)
 {
     setPlainText(tr("This TextEdit provides autocompletions for words that have more than"
                     " 3 characters. You can trigger autocompletion using ") +
@@ -78,7 +78,7 @@ TextEdit::~TextEdit()
 void TextEdit::setCompleter(QCompleter *completer)
 {
     if (c)
-        QObject::disconnect(c, 0, this, 0);
+        c->disconnect(this);
 
     c = completer;
 
@@ -101,7 +101,7 @@ QCompleter *TextEdit::completer() const
 //! [3]
 
 //! [4]
-void TextEdit::insertCompletion(const QString& completion)
+void TextEdit::insertCompletion(const QString &completion)
 {
     if (c->widget() != this)
         return;
@@ -150,18 +150,19 @@ void TextEdit::keyPressEvent(QKeyEvent *e)
        }
     }
 
-    bool isShortcut = ((e->modifiers() & Qt::ControlModifier) && e->key() == Qt::Key_E); // CTRL+E
+    const bool isShortcut = (e->modifiers().testFlag(Qt::ControlModifier) && e->key() == Qt::Key_E); // CTRL+E
     if (!c || !isShortcut) // do not process the shortcut when we have a completer
         QTextEdit::keyPressEvent(e);
 //! [7]
 
 //! [8]
-    const bool ctrlOrShift = e->modifiers() & (Qt::ControlModifier | Qt::ShiftModifier);
+    const bool ctrlOrShift = e->modifiers().testFlag(Qt::ControlModifier) ||
+                             e->modifiers().testFlag(Qt::ShiftModifier);
     if (!c || (ctrlOrShift && e->text().isEmpty()))
         return;
 
     static QString eow("~!@#$%^&*()_+{}|:\"<>?,./;'[]\\-="); // end of word
-    bool hasModifier = (e->modifiers() != Qt::NoModifier) && !ctrlOrShift;
+    const bool hasModifier = (e->modifiers() != Qt::NoModifier) && !ctrlOrShift;
     QString completionPrefix = textUnderCursor();
 
     if (!isShortcut && (hasModifier || e->text().isEmpty()|| completionPrefix.length() < 3
diff --git a/examples/widgets/tools/customcompleter/textedit.h b/examples/widgets/tools/customcompleter/textedit.h
index d0636ab670..788cb74ae1 100644
--- a/examples/widgets/tools/customcompleter/textedit.h
+++ b/examples/widgets/tools/customcompleter/textedit.h
@@ -63,7 +63,7 @@ class TextEdit : public QTextEdit
     Q_OBJECT
 
 public:
-    TextEdit(QWidget *parent = 0);
+    TextEdit(QWidget *parent = nullptr);
     ~TextEdit();
 
     void setCompleter(QCompleter *c);
@@ -80,7 +80,7 @@ private:
     QString textUnderCursor() const;
 
 private:
-    QCompleter *c;
+    QCompleter *c = nullptr;
 };
 //! [0]
 
diff --git a/examples/widgets/tools/echoplugin/echowindow/echointerface.h b/examples/widgets/tools/echoplugin/echowindow/echointerface.h
index 1915330e21..fb07f7fb79 100644
--- a/examples/widgets/tools/echoplugin/echowindow/echointerface.h
+++ b/examples/widgets/tools/echoplugin/echowindow/echointerface.h
@@ -51,13 +51,14 @@
 #ifndef ECHOINTERFACE_H
 #define ECHOINTERFACE_H
 
+#include <QObject>
 #include <QString>
 
 //! [0]
 class EchoInterface
 {
 public:
-    virtual ~EchoInterface() {}
+    virtual ~EchoInterface() = default;
     virtual QString echo(const QString &message) = 0;
 };
 
diff --git a/examples/widgets/tools/echoplugin/echowindow/echowindow.cpp b/examples/widgets/tools/echoplugin/echowindow/echowindow.cpp
index 6886a4cd88..dce6bdedc3 100644
--- a/examples/widgets/tools/echoplugin/echowindow/echowindow.cpp
+++ b/examples/widgets/tools/echoplugin/echowindow/echowindow.cpp
@@ -48,10 +48,17 @@
 **
 ****************************************************************************/
 
-#include <QtWidgets>
-
 #include "echowindow.h"
 
+#include <QCoreApplication>
+#include <QDir>
+#include <QLabel>
+#include <QLayout>
+#include <QLineEdit>
+#include <QMessageBox>
+#include <QPluginLoader>
+#include <QPushButton>
+
 //! [0]
 EchoWindow::EchoWindow()
 {
@@ -101,7 +108,7 @@ void EchoWindow::createGUI()
 //! [3]
 bool EchoWindow::loadPlugin()
 {
-    QDir pluginsDir(qApp->applicationDirPath());
+    QDir pluginsDir(QCoreApplication::applicationDirPath());
 #if defined(Q_OS_WIN)
     if (pluginsDir.dirName().toLower() == "debug" || pluginsDir.dirName().toLower() == "release")
         pluginsDir.cdUp();
@@ -121,6 +128,7 @@ bool EchoWindow::loadPlugin()
             echoInterface = qobject_cast<EchoInterface *>(plugin);
             if (echoInterface)
                 return true;
+            pluginLoader.unload();
         }
     }
 
diff --git a/examples/widgets/tools/echoplugin/echowindow/main.cpp b/examples/widgets/tools/echoplugin/echowindow/main.cpp
index 50e3c2763b..d3cf45fcde 100644
--- a/examples/widgets/tools/echoplugin/echowindow/main.cpp
+++ b/examples/widgets/tools/echoplugin/echowindow/main.cpp
@@ -48,7 +48,7 @@
 **
 ****************************************************************************/
 
-#include <QtWidgets>
+#include <QApplication>
 
 #include "echowindow.h"
 #include "echointerface.h"
diff --git a/examples/widgets/tools/echoplugin/plugin/echoplugin.cpp b/examples/widgets/tools/echoplugin/plugin/echoplugin.cpp
index de6b6a4462..c9dd93aab8 100644
--- a/examples/widgets/tools/echoplugin/plugin/echoplugin.cpp
+++ b/examples/widgets/tools/echoplugin/plugin/echoplugin.cpp
@@ -48,8 +48,6 @@
 **
 ****************************************************************************/
 
-#include <QtWidgets>
-
 #include "echoplugin.h"
 
 //! [0]
diff --git a/examples/widgets/tools/i18n/languagechooser.cpp b/examples/widgets/tools/i18n/languagechooser.cpp
index e61e4432e4..2ce3471873 100644
--- a/examples/widgets/tools/i18n/languagechooser.cpp
+++ b/examples/widgets/tools/i18n/languagechooser.cpp
@@ -48,34 +48,39 @@
 **
 ****************************************************************************/
 
-#include <QtWidgets>
-
 #include "languagechooser.h"
 #include "mainwindow.h"
 
-LanguageChooser::LanguageChooser(const QString& defaultLang, QWidget *parent)
+#include <QCoreApplication>
+#include <QCheckBox>
+#include <QDialogButtonBox>
+#include <QDir>
+#include <QGridLayout>
+#include <QGroupBox>
+#include <QPushButton>
+#include <QTranslator>
+
+LanguageChooser::LanguageChooser(const QString &defaultLang, QWidget *parent)
     : QDialog(parent, Qt::WindowStaysOnTopHint)
 {
     groupBox = new QGroupBox("Languages");
 
     QGridLayout *groupBoxLayout = new QGridLayout;
 
-    QStringList qmFiles = findQmFiles();
+    const QStringList qmFiles = findQmFiles();
     for (int i = 0; i < qmFiles.size(); ++i) {
-        QCheckBox *checkBox = new QCheckBox(languageName(qmFiles[i]));
-        qmFileForCheckBoxMap.insert(checkBox, qmFiles[i]);
-        connect(checkBox,
-                QOverload<bool>::of(&QCheckBox::toggled),
-                this,
-                &LanguageChooser::checkBoxToggled);
-        if (languageMatch(defaultLang, qmFiles[i]))
-                checkBox->setCheckState(Qt::Checked);
+        const QString &qmlFile = qmFiles.at(i);
+        QCheckBox *checkBox = new QCheckBox(languageName(qmlFile));
+        qmFileForCheckBoxMap.insert(checkBox, qmlFile);
+        connect(checkBox, &QCheckBox::toggled,
+                this, &LanguageChooser::checkBoxToggled);
+        if (languageMatch(defaultLang, qmlFile))
+            checkBox->setCheckState(Qt::Checked);
         groupBoxLayout->addWidget(checkBox, i / 2, i % 2);
     }
     groupBox->setLayout(groupBoxLayout);
 
     buttonBox = new QDialogButtonBox;
-
     showAllButton = buttonBox->addButton("Show All",
                                          QDialogButtonBox::ActionRole);
     hideAllButton = buttonBox->addButton("Hide All",
@@ -92,7 +97,7 @@ LanguageChooser::LanguageChooser(const QString& defaultLang, QWidget *parent)
     setWindowTitle("I18N");
 }
 
-bool LanguageChooser::languageMatch(const QString& lang, const QString& qmFile)
+bool LanguageChooser::languageMatch(const QString &lang, const QString &qmFile)
 {
     //qmFile: i18n_xx.qm
     const QString prefix = "i18n_";
@@ -110,21 +115,21 @@ bool LanguageChooser::eventFilter(QObject *object, QEvent *event)
                 checkBox->setChecked(false);
         }
     }
-    return QWidget::eventFilter(object, event);
+    return QDialog::eventFilter(object, event);
 }
 
 void LanguageChooser::closeEvent(QCloseEvent * /* event */)
 {
-    qApp->quit();
+    QCoreApplication::quit();
 }
 
 void LanguageChooser::checkBoxToggled()
 {
     QCheckBox *checkBox = qobject_cast<QCheckBox *>(sender());
-    MainWindow *window = mainWindowForCheckBoxMap[checkBox];
+    MainWindow *window = mainWindowForCheckBoxMap.value(checkBox);
     if (!window) {
         QTranslator translator;
-        translator.load(qmFileForCheckBoxMap[checkBox]);
+        translator.load(qmFileForCheckBoxMap.value(checkBox));
         qApp->installTranslator(&translator);
 
         window = new MainWindow;
diff --git a/examples/widgets/tools/i18n/languagechooser.h b/examples/widgets/tools/i18n/languagechooser.h
index 13363c7111..733cc50fd3 100644
--- a/examples/widgets/tools/i18n/languagechooser.h
+++ b/examples/widgets/tools/i18n/languagechooser.h
@@ -52,7 +52,7 @@
 #define LANGUAGECHOOSER_H
 
 #include <QDialog>
-#include <QMap>
+#include <QHash>
 #include <QStringList>
 
 QT_BEGIN_NAMESPACE
@@ -68,7 +68,7 @@ class LanguageChooser : public QDialog
     Q_OBJECT
 
 public:
-    explicit LanguageChooser(const QString& defaultLang = QString(), QWidget *parent = 0);
+    explicit LanguageChooser(const QString &defaultLang = QString(), QWidget *parent = nullptr);
 
 protected:
     bool eventFilter(QObject *object, QEvent *event) override;
@@ -80,17 +80,17 @@ private slots:
     void hideAll();
 
 private:
-    QStringList findQmFiles();
-    QString languageName(const QString &qmFile);
-    QColor colorForLanguage(const QString &language);
-    static bool languageMatch(const QString& lang, const QString& qmFile);
+    static QStringList findQmFiles();
+    static QString languageName(const QString &qmFile);
+    static QColor colorForLanguage(const QString &language);
+    static bool languageMatch(const QString &lang, const QString &qmFile);
 
     QGroupBox *groupBox;
     QDialogButtonBox *buttonBox;
     QAbstractButton *showAllButton;
     QAbstractButton *hideAllButton;
-    QMap<QCheckBox *, QString> qmFileForCheckBoxMap;
-    QMap<QCheckBox *, MainWindow *> mainWindowForCheckBoxMap;
+    QHash<QCheckBox *, QString> qmFileForCheckBoxMap;
+    QHash<QCheckBox *, MainWindow *> mainWindowForCheckBoxMap;
 };
 
 #endif
diff --git a/examples/widgets/tools/i18n/mainwindow.cpp b/examples/widgets/tools/i18n/mainwindow.cpp
index 6ebfddfa98..a107a819ca 100644
--- a/examples/widgets/tools/i18n/mainwindow.cpp
+++ b/examples/widgets/tools/i18n/mainwindow.cpp
@@ -48,18 +48,26 @@
 **
 ****************************************************************************/
 
-#include <QtWidgets>
-
 #include "mainwindow.h"
 
+#include <QAction>
+#include <QCoreApplication>
+#include <QGroupBox>
+#include <QListWidget>
+#include <QMenuBar>
+#include <QRadioButton>
+#include <QStatusBar>
+#include <QVBoxLayout>
+
 static const char * const listEntries[] = {
     QT_TRANSLATE_NOOP("MainWindow", "First"),
     QT_TRANSLATE_NOOP("MainWindow", "Second"),
     QT_TRANSLATE_NOOP("MainWindow", "Third"),
-    0
+    nullptr
 };
 
-MainWindow::MainWindow()
+MainWindow::MainWindow(QWidget *parent)
+    : QMainWindow(parent)
 {
     centralWidget = new QWidget;
     setCentralWidget(centralWidget);
@@ -67,8 +75,8 @@ MainWindow::MainWindow()
     createGroupBox();
 
     listWidget = new QListWidget;
-    for (int i = 0; listEntries[i]; ++i)
-        listWidget->addItem(tr(listEntries[i]));
+    for (const char *entry : listEntries)
+        listWidget->addItem(tr(entry));
 
     QVBoxLayout *mainLayout = new QVBoxLayout;
     mainLayout->addWidget(groupBox);
@@ -76,7 +84,7 @@ MainWindow::MainWindow()
     centralWidget->setLayout(mainLayout);
 
     exitAction = new QAction(tr("E&xit"), this);
-    connect(exitAction, &QAction::triggered, qApp, QApplication::quit);
+    connect(exitAction, &QAction::triggered, qApp, QCoreApplication::quit);
 
     fileMenu = menuBar()->addMenu(tr("&File"));
     fileMenu->setPalette(QPalette(Qt::red));
diff --git a/examples/widgets/tools/i18n/mainwindow.h b/examples/widgets/tools/i18n/mainwindow.h
index e011151894..105472d60c 100644
--- a/examples/widgets/tools/i18n/mainwindow.h
+++ b/examples/widgets/tools/i18n/mainwindow.h
@@ -67,7 +67,7 @@ class MainWindow : public QMainWindow
     Q_OBJECT
 
 public:
-    MainWindow();
+    MainWindow(QWidget *parent = nullptr);
 
 private:
     void createGroupBox();
diff --git a/examples/widgets/tools/plugandpaint/app/mainwindow.cpp b/examples/widgets/tools/plugandpaint/app/mainwindow.cpp
index ebe1150eea..ff3b3614af 100644
--- a/examples/widgets/tools/plugandpaint/app/mainwindow.cpp
+++ b/examples/widgets/tools/plugandpaint/app/mainwindow.cpp
@@ -49,8 +49,8 @@
 ****************************************************************************/
 
 
-#include "interfaces.h"
 #include "mainwindow.h"
+#include "interfaces.h"
 #include "paintarea.h"
 #include "plugindialog.h"
 
@@ -67,9 +67,8 @@
 #include <QScrollArea>
 #include <QTimer>
 
-MainWindow::MainWindow() :
-    paintArea(new PaintArea),
-    scrollArea(new QScrollArea)
+MainWindow::MainWindow() : paintArea(new PaintArea)
+    , scrollArea(new QScrollArea)
 {
     scrollArea->setBackgroundRole(QPalette::Dark);
     scrollArea->setWidget(paintArea);
@@ -136,7 +135,11 @@ void MainWindow::brushWidth()
 void MainWindow::changeBrush()
 {
     auto action = qobject_cast<QAction *>(sender());
+    if (!action)
+      return;
     auto iBrush = qobject_cast<BrushInterface *>(action->parent());
+    if (!iBrush)
+      return;
     const QString brush = action->text();
 
     paintArea->setBrush(iBrush, brush);
@@ -147,7 +150,11 @@ void MainWindow::changeBrush()
 void MainWindow::insertShape()
 {
     auto action = qobject_cast<QAction *>(sender());
+    if (!action)
+      return;
     auto iShape = qobject_cast<ShapeInterface *>(action->parent());
+    if (!iShape)
+      return;
 
     const QPainterPath path = iShape->generateShape(action->text(), this);
     if (!path.isEmpty())
@@ -159,7 +166,11 @@ void MainWindow::insertShape()
 void MainWindow::applyFilter()
 {
     auto action = qobject_cast<QAction *>(sender());
+    if (!action)
+      return;
     auto iFilter = qobject_cast<FilterInterface *>(action->parent());
+    if (!iFilter)
+      return;
 
     const QImage image = iFilter->filterImage(action->text(), paintArea->image(),
                                               this);
@@ -247,7 +258,7 @@ void MainWindow::loadPlugins()
         populateMenus(plugin);
 //! [4] //! [5]
 
-    pluginsDir = QDir(qApp->applicationDirPath());
+    pluginsDir = QDir(QCoreApplication::applicationDirPath());
 
 #if defined(Q_OS_WIN)
     if (pluginsDir.dirName().toLower() == "debug" || pluginsDir.dirName().toLower() == "release")
diff --git a/examples/widgets/tools/plugandpaint/app/paintarea.cpp b/examples/widgets/tools/plugandpaint/app/paintarea.cpp
index e225d78398..92b8ea4777 100644
--- a/examples/widgets/tools/plugandpaint/app/paintarea.cpp
+++ b/examples/widgets/tools/plugandpaint/app/paintarea.cpp
@@ -49,14 +49,13 @@
 ****************************************************************************/
 
 
-#include "interfaces.h"
 #include "paintarea.h"
+#include "interfaces.h"
 
 #include <QMouseEvent>
 #include <QPainter>
 
-PaintArea::PaintArea(QWidget *parent) :
-    QWidget(parent)
+PaintArea::PaintArea(QWidget *parent) : QWidget(parent)
 {
     setAttribute(Qt::WA_StaticContents);
     setAttribute(Qt::WA_OpaquePaintEvent);
diff --git a/examples/widgets/tools/plugandpaint/app/plugindialog.cpp b/examples/widgets/tools/plugandpaint/app/plugindialog.cpp
index 84bd364b41..204d6ffec4 100644
--- a/examples/widgets/tools/plugandpaint/app/plugindialog.cpp
+++ b/examples/widgets/tools/plugandpaint/app/plugindialog.cpp
@@ -49,8 +49,8 @@
 ****************************************************************************/
 
 
-#include "interfaces.h"
 #include "plugindialog.h"
+#include "interfaces.h"
 
 #include <QDir>
 #include <QGridLayout>
diff --git a/examples/widgets/tools/plugandpaint/plugins/basictools/basictoolsplugin.cpp b/examples/widgets/tools/plugandpaint/plugins/basictools/basictoolsplugin.cpp
index 3b465565ba..64f9f7a0d9 100644
--- a/examples/widgets/tools/plugandpaint/plugins/basictools/basictoolsplugin.cpp
+++ b/examples/widgets/tools/plugandpaint/plugins/basictools/basictoolsplugin.cpp
@@ -50,10 +50,10 @@
 
 #include "basictoolsplugin.h"
 
+#include <QInputDialog>
+#include <QPainter>
+#include <QRandomGenerator>
 #include <QtMath>
-#include <QtWidgets>
-
-#include <stdlib.h>
 
 //! [0]
 QStringList BasicToolsPlugin::brushes() const
diff --git a/examples/widgets/tools/plugandpaint/plugins/basictools/basictoolsplugin.h b/examples/widgets/tools/plugandpaint/plugins/basictools/basictoolsplugin.h
index fd9bb9e5f3..1d9d170daa 100644
--- a/examples/widgets/tools/plugandpaint/plugins/basictools/basictoolsplugin.h
+++ b/examples/widgets/tools/plugandpaint/plugins/basictools/basictoolsplugin.h
@@ -54,12 +54,12 @@
 //! [0]
 #include <interfaces.h>
 
-#include <QRect>
+#include <QImage>
 #include <QObject>
-#include <QtPlugin>
-#include <QStringList>
 #include <QPainterPath>
-#include <QImage>
+#include <QRect>
+#include <QStringList>
+#include <QtPlugin>
 
 //! [1]
 class BasicToolsPlugin : public QObject,
diff --git a/examples/widgets/tools/plugandpaint/plugins/extrafilters/extrafiltersplugin.cpp b/examples/widgets/tools/plugandpaint/plugins/extrafilters/extrafiltersplugin.cpp
index 48717e34f6..30c616a830 100644
--- a/examples/widgets/tools/plugandpaint/plugins/extrafilters/extrafiltersplugin.cpp
+++ b/examples/widgets/tools/plugandpaint/plugins/extrafilters/extrafiltersplugin.cpp
@@ -50,10 +50,7 @@
 
 #include "extrafiltersplugin.h"
 
-#include <QtWidgets>
-
-#include <math.h>
-#include <stdlib.h>
+#include <QInputDialog>
 
 QStringList ExtraFiltersPlugin::filters() const
 {
diff --git a/examples/widgets/tools/regexp/regexpdialog.h b/examples/widgets/tools/regexp/regexpdialog.h
index 4bdc18da15..2f701a7228 100644
--- a/examples/widgets/tools/regexp/regexpdialog.h
+++ b/examples/widgets/tools/regexp/regexpdialog.h
@@ -65,7 +65,7 @@ class RegExpDialog : public QDialog
     Q_OBJECT
 
 public:
-    RegExpDialog(QWidget *parent = 0);
+    RegExpDialog(QWidget *parent = nullptr);
 
 private slots:
     void refresh();
diff --git a/examples/widgets/tools/regularexpression/regularexpressiondialog.h b/examples/widgets/tools/regularexpression/regularexpressiondialog.h
index ba5b38b5e3..8fe85afe56 100644
--- a/examples/widgets/tools/regularexpression/regularexpressiondialog.h
+++ b/examples/widgets/tools/regularexpression/regularexpressiondialog.h
@@ -70,7 +70,7 @@ class RegularExpressionDialog : public QDialog
     Q_OBJECT
 
 public:
-    RegularExpressionDialog(QWidget *parent = 0);
+    RegularExpressionDialog(QWidget *parent = nullptr);
 
 private:
     void refresh();
diff --git a/examples/widgets/tools/settingseditor/locationdialog.cpp b/examples/widgets/tools/settingseditor/locationdialog.cpp
index 5b6e2652bb..99c9834a63 100644
--- a/examples/widgets/tools/settingseditor/locationdialog.cpp
+++ b/examples/widgets/tools/settingseditor/locationdialog.cpp
@@ -48,10 +48,20 @@
 **
 ****************************************************************************/
 
-#include <QtWidgets>
-
 #include "locationdialog.h"
 
+#include <QBoxLayout>
+#include <QComboBox>
+#include <QDialogButtonBox>
+#include <QDir>
+#include <QPushButton>
+#include <QGroupBox>
+#include <QHeaderView>
+#include <QLabel>
+#include <QLineEdit>
+#include <QTableWidget>
+#include <QTableWidgetItem>
+
 LocationDialog::LocationDialog(QWidget *parent)
     : QDialog(parent)
 {
@@ -91,8 +101,7 @@ LocationDialog::LocationDialog(QWidget *parent)
 
     locationsGroupBox = new QGroupBox(tr("Setting Locations"));
 
-    QStringList labels;
-    labels << tr("Location") << tr("Access");
+    const QStringList labels{tr("Location"), tr("Access")};
 
     locationsTable = new QTableWidget;
     locationsTable->setSelectionMode(QAbstractItemView::SingleSelection);
diff --git a/examples/widgets/tools/settingseditor/locationdialog.h b/examples/widgets/tools/settingseditor/locationdialog.h
index c25b01effd..cd2efecb0b 100644
--- a/examples/widgets/tools/settingseditor/locationdialog.h
+++ b/examples/widgets/tools/settingseditor/locationdialog.h
@@ -68,7 +68,7 @@ class LocationDialog : public QDialog
     Q_OBJECT
 
 public:
-    LocationDialog(QWidget *parent = 0);
+    LocationDialog(QWidget *parent = nullptr);
 
     QSettings::Format format() const;
     QSettings::Scope scope() const;
diff --git a/examples/widgets/tools/settingseditor/mainwindow.cpp b/examples/widgets/tools/settingseditor/mainwindow.cpp
index a7a1e9b415..b9c2193ccb 100644
--- a/examples/widgets/tools/settingseditor/mainwindow.cpp
+++ b/examples/widgets/tools/settingseditor/mainwindow.cpp
@@ -48,15 +48,23 @@
 **
 ****************************************************************************/
 
-#include <QtWidgets>
-
 #include "locationdialog.h"
 #include "mainwindow.h"
 #include "settingstree.h"
 
-MainWindow::MainWindow()
-    : settingsTree(new SettingsTree)
-    , locationDialog(nullptr)
+#include <QAction>
+#include <QApplication>
+#include <QDesktopWidget>
+#include <QFileDialog>
+#include <QInputDialog>
+#include <QLineEdit>
+#include <QMenuBar>
+#include <QMessageBox>
+#include <QStandardPaths>
+#include <QStatusBar>
+
+MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent)
+    , settingsTree(new SettingsTree)
 {
     setCentralWidget(settingsTree);
 
diff --git a/examples/widgets/tools/settingseditor/mainwindow.h b/examples/widgets/tools/settingseditor/mainwindow.h
index 373c982afe..b1115005a9 100644
--- a/examples/widgets/tools/settingseditor/mainwindow.h
+++ b/examples/widgets/tools/settingseditor/mainwindow.h
@@ -68,7 +68,7 @@ class MainWindow : public QMainWindow
 public:
     typedef QSharedPointer<QSettings> SettingsPtr;
 
-    MainWindow();
+    MainWindow(QWidget *parent = nullptr);
 
 private slots:
     void openSettings();
@@ -81,11 +81,11 @@ private:
     void createActions();
     void setSettingsObject(const SettingsPtr &settings);
 
-    SettingsTree *settingsTree;
-    LocationDialog *locationDialog;
-    QAction *refreshAct;
-    QAction *autoRefreshAct;
-    QAction *fallbacksAct;
+    SettingsTree *settingsTree = nullptr;
+    LocationDialog *locationDialog = nullptr;
+    QAction *refreshAct = nullptr;
+    QAction *autoRefreshAct = nullptr;
+    QAction *fallbacksAct = nullptr;
 };
 
 #endif
diff --git a/examples/widgets/tools/settingseditor/settingstree.cpp b/examples/widgets/tools/settingseditor/settingstree.cpp
index 8585792787..b263746847 100644
--- a/examples/widgets/tools/settingseditor/settingstree.cpp
+++ b/examples/widgets/tools/settingseditor/settingstree.cpp
@@ -48,20 +48,20 @@
 **
 ****************************************************************************/
 
-#include <QtWidgets>
-
 #include "settingstree.h"
 #include "variantdelegate.h"
 
+#include <QApplication>
+#include <QDesktopWidget>
+#include <QHeaderView>
+#include <QSettings>
+
 SettingsTree::SettingsTree(QWidget *parent)
     : QTreeWidget(parent)
-    , autoRefresh(false)
 {
     setItemDelegate(new VariantDelegate(this));
 
-    QStringList labels;
-    labels << tr("Setting") << tr("Type") << tr("Value");
-    setHeaderLabels(labels);
+    setHeaderLabels({tr("Setting"), tr("Type"), tr("Value")});
     header()->setSectionResizeMode(0, QHeaderView::ResizeToContents);
     header()->setSectionResizeMode(1, QHeaderView::ResizeToContents);
     header()->setSectionResizeMode(2, QHeaderView::Stretch);
@@ -77,10 +77,6 @@ SettingsTree::SettingsTree(QWidget *parent)
     connect(&refreshTimer, &QTimer::timeout, this, &SettingsTree::maybeRefresh);
 }
 
-SettingsTree::~SettingsTree()
-{
-}
-
 void SettingsTree::setSettingsObject(const SettingsPtr &newSettings)
 {
     settings = newSettings;
@@ -137,7 +133,7 @@ void SettingsTree::refresh()
                this, &SettingsTree::updateSetting);
 
     settings->sync();
-    updateChildItems(0);
+    updateChildItems(nullptr);
 
     connect(this, &QTreeWidget::itemChanged,
             this, &SettingsTree::updateSetting);
@@ -228,7 +224,7 @@ void SettingsTree::updateChildItems(QTreeWidgetItem *parent)
 QTreeWidgetItem *SettingsTree::createItem(const QString &text,
                                           QTreeWidgetItem *parent, int index)
 {
-    QTreeWidgetItem *after = 0;
+    QTreeWidgetItem *after = nullptr;
     if (index != 0)
         after = childAt(parent, index - 1);
 
@@ -243,24 +239,18 @@ QTreeWidgetItem *SettingsTree::createItem(const QString &text,
     return item;
 }
 
-QTreeWidgetItem *SettingsTree::childAt(QTreeWidgetItem *parent, int index)
+QTreeWidgetItem *SettingsTree::childAt(QTreeWidgetItem *parent, int index) const
 {
-    if (parent)
-        return parent->child(index);
-    else
-        return topLevelItem(index);
+    return (parent ? parent->child(index) : topLevelItem(index));
 }
 
-int SettingsTree::childCount(QTreeWidgetItem *parent)
+int SettingsTree::childCount(QTreeWidgetItem *parent) const
 {
-    if (parent)
-        return parent->childCount();
-    else
-        return topLevelItemCount();
+    return (parent ? parent->childCount() : topLevelItemCount());
 }
 
 int SettingsTree::findChild(QTreeWidgetItem *parent, const QString &text,
-                            int startIndex)
+                            int startIndex) const
 {
     for (int i = startIndex; i < childCount(parent); ++i) {
         if (childAt(parent, i)->text(0) == text)
diff --git a/examples/widgets/tools/settingseditor/settingstree.h b/examples/widgets/tools/settingseditor/settingstree.h
index 15efa0e6aa..3e9e9658ce 100644
--- a/examples/widgets/tools/settingseditor/settingstree.h
+++ b/examples/widgets/tools/settingseditor/settingstree.h
@@ -65,10 +65,9 @@ class SettingsTree : public QTreeWidget
     Q_OBJECT
 
 public:
-    typedef QSharedPointer<QSettings> SettingsPtr;
+    using SettingsPtr = QSharedPointer<QSettings>;
 
-    SettingsTree(QWidget *parent = 0);
-    ~SettingsTree();
+    SettingsTree(QWidget *parent = nullptr);
 
     void setSettingsObject(const SettingsPtr &settings);
     QSize sizeHint() const override;
@@ -89,16 +88,16 @@ private:
     void updateChildItems(QTreeWidgetItem *parent);
     QTreeWidgetItem *createItem(const QString &text, QTreeWidgetItem *parent,
                                 int index);
-    QTreeWidgetItem *childAt(QTreeWidgetItem *parent, int index);
-    int childCount(QTreeWidgetItem *parent);
-    int findChild(QTreeWidgetItem *parent, const QString &text, int startIndex);
+    QTreeWidgetItem *childAt(QTreeWidgetItem *parent, int index) const;
+    int childCount(QTreeWidgetItem *parent) const;
+    int findChild(QTreeWidgetItem *parent, const QString &text, int startIndex) const;
     void moveItemForward(QTreeWidgetItem *parent, int oldIndex, int newIndex);
 
     SettingsPtr settings;
     QTimer refreshTimer;
-    bool autoRefresh;
     QIcon groupIcon;
     QIcon keyIcon;
+    bool autoRefresh = false;
 };
 
 #endif
diff --git a/examples/widgets/tools/settingseditor/variantdelegate.cpp b/examples/widgets/tools/settingseditor/variantdelegate.cpp
index 266754ca4d..9772fe8a41 100644
--- a/examples/widgets/tools/settingseditor/variantdelegate.cpp
+++ b/examples/widgets/tools/settingseditor/variantdelegate.cpp
@@ -48,12 +48,14 @@
 **
 ****************************************************************************/
 
-#include <QtWidgets>
-
 #include "variantdelegate.h"
 
+#include <QDateTime>
+#include <QLineEdit>
+#include <QRegularExpressionValidator>
+
 VariantDelegate::VariantDelegate(QObject *parent)
-    : QItemDelegate(parent)
+    : QStyledItemDelegate(parent)
 {
     boolExp.setPattern("true|false");
     boolExp.setPatternOptions(QRegularExpression::CaseInsensitiveOption);
@@ -82,12 +84,12 @@ void VariantDelegate::paint(QPainter *painter,
         if (!isSupportedType(value.type())) {
             QStyleOptionViewItem myOption = option;
             myOption.state &= ~QStyle::State_Enabled;
-            QItemDelegate::paint(painter, myOption, index);
+            QStyledItemDelegate::paint(painter, myOption, index);
             return;
         }
     }
 
-    QItemDelegate::paint(painter, option, index);
+    QStyledItemDelegate::paint(painter, option, index);
 }
 
 QWidget *VariantDelegate::createEditor(QWidget *parent,
@@ -95,11 +97,11 @@ QWidget *VariantDelegate::createEditor(QWidget *parent,
         const QModelIndex &index) const
 {
     if (index.column() != 2)
-        return 0;
+        return nullptr;
 
     QVariant originalValue = index.model()->data(index, Qt::UserRole);
     if (!isSupportedType(originalValue.type()))
-        return 0;
+        return nullptr;
 
     QLineEdit *lineEdit = new QLineEdit(parent);
     lineEdit->setFrame(false);
@@ -149,7 +151,7 @@ QWidget *VariantDelegate::createEditor(QWidget *parent,
         regExp = unsignedIntegerExp;
         break;
     default:
-        ;
+        break;
     }
 
     if (regExp.isValid()) {
diff --git a/examples/widgets/tools/settingseditor/variantdelegate.h b/examples/widgets/tools/settingseditor/variantdelegate.h
index 7cd9fa9ee8..68f21fa3f6 100644
--- a/examples/widgets/tools/settingseditor/variantdelegate.h
+++ b/examples/widgets/tools/settingseditor/variantdelegate.h
@@ -51,15 +51,15 @@
 #ifndef VARIANTDELEGATE_H
 #define VARIANTDELEGATE_H
 
-#include <QItemDelegate>
+#include <QStyledItemDelegate>
 #include <QRegularExpression>
 
-class VariantDelegate : public QItemDelegate
+class VariantDelegate : public QStyledItemDelegate
 {
     Q_OBJECT
 
 public:
-    VariantDelegate(QObject *parent = 0);
+    VariantDelegate(QObject *parent = nullptr);
 
     void paint(QPainter *painter, const QStyleOptionViewItem &option,
                const QModelIndex &index) const override;
diff --git a/examples/widgets/tools/styleplugin/plugin/simplestyle.cpp b/examples/widgets/tools/styleplugin/plugin/simplestyle.cpp
index 59da6a8672..765c9c2745 100644
--- a/examples/widgets/tools/styleplugin/plugin/simplestyle.cpp
+++ b/examples/widgets/tools/styleplugin/plugin/simplestyle.cpp
@@ -48,8 +48,6 @@
 **
 ****************************************************************************/
 
-#include <QtWidgets>
-
 #include "simplestyle.h"
 
 void SimpleStyle::polish(QPalette &palette)
diff --git a/examples/widgets/tools/styleplugin/plugin/simplestyle.h b/examples/widgets/tools/styleplugin/plugin/simplestyle.h
index 51d6d5b77e..4f49de8cbc 100644
--- a/examples/widgets/tools/styleplugin/plugin/simplestyle.h
+++ b/examples/widgets/tools/styleplugin/plugin/simplestyle.h
@@ -53,16 +53,12 @@
 
 #include <QProxyStyle>
 
-QT_BEGIN_NAMESPACE
-class QPalette;
-QT_END_NAMESPACE
-
 class SimpleStyle : public QProxyStyle
 {
     Q_OBJECT
 
 public:
-    SimpleStyle() {};
+    SimpleStyle() = default;
 
     void polish(QPalette &palette) override;
 };
diff --git a/examples/widgets/tools/styleplugin/plugin/simplestyleplugin.cpp b/examples/widgets/tools/styleplugin/plugin/simplestyleplugin.cpp
index 344e46061c..cbe7c15cc0 100644
--- a/examples/widgets/tools/styleplugin/plugin/simplestyleplugin.cpp
+++ b/examples/widgets/tools/styleplugin/plugin/simplestyleplugin.cpp
@@ -48,15 +48,13 @@
 **
 ****************************************************************************/
 
-#include <QtWidgets>
-
 #include "simplestyleplugin.h"
 #include "simplestyle.h"
 
 //! [0]
 QStringList SimpleStylePlugin::keys() const
 {
-    return QStringList() << "SimpleStyle";
+    return {"SimpleStyle"};
 }
 //! [0]
 
@@ -65,6 +63,6 @@ QStyle *SimpleStylePlugin::create(const QString &key)
 {
     if (key.toLower() == "simplestyle")
         return new SimpleStyle;
-    return 0;
+    return nullptr;
 }
 //! [1]
diff --git a/examples/widgets/tools/styleplugin/plugin/simplestyleplugin.h b/examples/widgets/tools/styleplugin/plugin/simplestyleplugin.h
index 88805d4887..3ce37410eb 100644
--- a/examples/widgets/tools/styleplugin/plugin/simplestyleplugin.h
+++ b/examples/widgets/tools/styleplugin/plugin/simplestyleplugin.h
@@ -53,11 +53,6 @@
 
 #include <QStylePlugin>
 
-QT_BEGIN_NAMESPACE
-class QStringList;
-class QStyle;
-QT_END_NAMESPACE
-
 //! [0]
 class SimpleStylePlugin : public QStylePlugin
 {
@@ -65,7 +60,7 @@ class SimpleStylePlugin : public QStylePlugin
     Q_PLUGIN_METADATA(IID "org.qt-project.Qt.QStyleFactoryInterface" FILE "simplestyle.json")
 
 public:
-    SimpleStylePlugin() {}
+    SimpleStylePlugin() = default;
 
     QStringList keys() const;
     QStyle *create(const QString &key) override;
diff --git a/examples/widgets/tools/styleplugin/stylewindow/main.cpp b/examples/widgets/tools/styleplugin/stylewindow/main.cpp
index 93816d393d..ff29eb119e 100644
--- a/examples/widgets/tools/styleplugin/stylewindow/main.cpp
+++ b/examples/widgets/tools/styleplugin/stylewindow/main.cpp
@@ -48,7 +48,8 @@
 **
 ****************************************************************************/
 
-#include <QtWidgets>
+#include <QApplication>
+#include <QStyleFactory>
 
 #include "stylewindow.h"
 
diff --git a/examples/widgets/tools/styleplugin/stylewindow/stylewindow.cpp b/examples/widgets/tools/styleplugin/stylewindow/stylewindow.cpp
index 7a05a3ae92..90413ed12e 100644
--- a/examples/widgets/tools/styleplugin/stylewindow/stylewindow.cpp
+++ b/examples/widgets/tools/styleplugin/stylewindow/stylewindow.cpp
@@ -48,7 +48,9 @@
 **
 ****************************************************************************/
 
-#include <QtWidgets>
+#include <QGridLayout>
+#include <QGroupBox>
+#include <QPushButton>
 
 #include "stylewindow.h"
 
diff --git a/examples/widgets/tools/treemodelcompleter/mainwindow.cpp b/examples/widgets/tools/treemodelcompleter/mainwindow.cpp
index dec3cb0496..302ccc436c 100644
--- a/examples/widgets/tools/treemodelcompleter/mainwindow.cpp
+++ b/examples/widgets/tools/treemodelcompleter/mainwindow.cpp
@@ -48,13 +48,28 @@
 **
 ****************************************************************************/
 
-#include <QtWidgets>
-#include "treemodelcompleter.h"
 #include "mainwindow.h"
+#include "treemodelcompleter.h"
+
+#include <QAbstractProxyModel>
+#include <QAction>
+#include <QApplication>
+#include <QCheckBox>
+#include <QComboBox>
+#include <QFile>
+#include <QGridLayout>
+#include <QHeaderView>
+#include <QLabel>
+#include <QLineEdit>
+#include <QMenuBar>
+#include <QMessageBox>
+#include <QStandardItemModel>
+#include <QStringListModel>
+#include <QTreeView>
 
 //! [0]
 MainWindow::MainWindow(QWidget *parent)
-    : QMainWindow(parent), completer(0), lineEdit(0)
+    : QMainWindow(parent)
 {
     createMenu();
 
@@ -151,10 +166,10 @@ void MainWindow::createMenu()
     connect(aboutAct, &QAction::triggered, this, &MainWindow::about);
     connect(aboutQtAct, &QAction::triggered, qApp, &QApplication::aboutQt);
 
-    QMenu* fileMenu = menuBar()->addMenu(tr("File"));
+    QMenu *fileMenu = menuBar()->addMenu(tr("File"));
     fileMenu->addAction(exitAction);
 
-    QMenu* helpMenu = menuBar()->addMenu(tr("About"));
+    QMenu *helpMenu = menuBar()->addMenu(tr("About"));
     helpMenu->addAction(aboutAct);
     helpMenu->addAction(aboutQtAct);
 }
@@ -175,7 +190,7 @@ void MainWindow::changeMode(int index)
 }
 //! [5]
 
-QAbstractItemModel *MainWindow::modelFromFile(const QString& fileName)
+QAbstractItemModel *MainWindow::modelFromFile(const QString &fileName)
 {
     QFile file(fileName);
     if (!file.open(QFile::ReadOnly))
@@ -184,39 +199,35 @@ QAbstractItemModel *MainWindow::modelFromFile(const QString& fileName)
 #ifndef QT_NO_CURSOR
     QGuiApplication::setOverrideCursor(QCursor(Qt::WaitCursor));
 #endif
-    QStringList words;
 
     QStandardItemModel *model = new QStandardItemModel(completer);
     QVector<QStandardItem *> parents(10);
     parents[0] = model->invisibleRootItem();
 
+    QRegularExpression re("^\\s+");
     while (!file.atEnd()) {
-        QString line = file.readLine();
-        QString trimmedLine = line.trimmed();
-        if (line.isEmpty() || trimmedLine.isEmpty())
+        const QString line = QString::fromUtf8(file.readLine()).trimmed();
+        const QString trimmedLine = line.trimmed();
+        if (trimmedLine.isEmpty())
             continue;
 
-        QRegularExpression re("^\\s+");
-        QRegularExpressionMatch match = re.match(line);
+        const QRegularExpressionMatch match = re.match(line);
         int nonws = match.capturedStart();
         int level = 0;
         if (nonws == -1) {
             level = 0;
         } else {
-            if (line.startsWith("\t")) {
-                level = match.capturedLength();
-            } else {
-                level = match.capturedLength()/4;
-            }
+            const int capLen = match.capturedLength();
+            level = line.startsWith(QLatin1Char('\t')) ? capLen / 4 : capLen;
         }
 
-        if (level+1 >= parents.size())
-            parents.resize(parents.size()*2);
+        if (level + 1 >= parents.size())
+            parents.resize(parents.size() * 2);
 
         QStandardItem *item = new QStandardItem;
         item->setText(trimmedLine);
         parents[level]->appendRow(item);
-        parents[level+1] = item;
+        parents[level + 1] = item;
     }
 
 #ifndef QT_NO_CURSOR
@@ -252,7 +263,7 @@ void MainWindow::changeCase(int cs)
 }
 //! [7]
 
-void MainWindow::updateContentsLabel(const QString& sep)
+void MainWindow::updateContentsLabel(const QString &sep)
 {
     contentsLabel->setText(tr("Type path from model above with items at each level separated by a '%1'").arg(sep));
 }
diff --git a/examples/widgets/tools/treemodelcompleter/mainwindow.h b/examples/widgets/tools/treemodelcompleter/mainwindow.h
index 2edcd5aab0..87f492c4ac 100644
--- a/examples/widgets/tools/treemodelcompleter/mainwindow.h
+++ b/examples/widgets/tools/treemodelcompleter/mainwindow.h
@@ -60,8 +60,6 @@ class QAbstractItemModel;
 class QComboBox;
 class QLabel;
 class QLineEdit;
-class QProgressBar;
-class QCheckBox;
 class QTreeView;
 QT_END_NAMESPACE
 
@@ -71,27 +69,27 @@ class MainWindow : public QMainWindow
     Q_OBJECT
 
 public:
-    MainWindow(QWidget *parent = 0);
+    MainWindow(QWidget *parent = nullptr);
 
 private slots:
     void about();
     void changeCase(int);
     void changeMode(int);
-    void highlight(const QModelIndex&);
-    void updateContentsLabel(const QString&);
+    void highlight(const QModelIndex &index);
+    void updateContentsLabel(const QString &sep);
 //! [0]
 
 //! [1]
 private:
     void createMenu();
-    QAbstractItemModel *modelFromFile(const QString& fileName);
+    QAbstractItemModel *modelFromFile(const QString &fileName);
 
-    QTreeView *treeView;
-    QComboBox *caseCombo;
-    QComboBox *modeCombo;
-    QLabel *contentsLabel;
-    TreeModelCompleter *completer;
-    QLineEdit *lineEdit;
+    QTreeView *treeView = nullptr;
+    QComboBox *caseCombo = nullptr;
+    QComboBox *modeCombo = nullptr;
+    QLabel *contentsLabel = nullptr;
+    TreeModelCompleter *completer = nullptr;
+    QLineEdit *lineEdit = nullptr;
 };
 //! [1]
 
diff --git a/examples/widgets/tools/treemodelcompleter/treemodelcompleter.cpp b/examples/widgets/tools/treemodelcompleter/treemodelcompleter.cpp
index cab0476e3c..8930c815d5 100644
--- a/examples/widgets/tools/treemodelcompleter/treemodelcompleter.cpp
+++ b/examples/widgets/tools/treemodelcompleter/treemodelcompleter.cpp
@@ -80,26 +80,20 @@ QString TreeModelCompleter::separator() const
 //! [3]
 QStringList TreeModelCompleter::splitPath(const QString &path) const
 {
-    if (sep.isNull()) {
-        return QCompleter::splitPath(path);
-    }
-
-    return path.split(sep);
+    return (sep.isNull() ? QCompleter::splitPath(path) : path.split(sep));
 }
 //! [3]
 
 //! [4]
 QString TreeModelCompleter::pathFromIndex(const QModelIndex &index) const
 {
-    if (sep.isNull()) {
+    if (sep.isNull())
         return QCompleter::pathFromIndex(index);
-    }
 
     // navigate up and accumulate data
     QStringList dataList;
-    for (QModelIndex i = index; i.isValid(); i = i.parent()) {
+    for (QModelIndex i = index; i.isValid(); i = i.parent())
         dataList.prepend(model()->data(i, completionRole()).toString());
-    }
 
     return dataList.join(sep);
 }
diff --git a/examples/widgets/tools/treemodelcompleter/treemodelcompleter.h b/examples/widgets/tools/treemodelcompleter/treemodelcompleter.h
index 1d28fddee0..d7d1852cc7 100644
--- a/examples/widgets/tools/treemodelcompleter/treemodelcompleter.h
+++ b/examples/widgets/tools/treemodelcompleter/treemodelcompleter.h
@@ -60,8 +60,8 @@ class TreeModelCompleter : public QCompleter
     Q_PROPERTY(QString separator READ separator WRITE setSeparator)
 
 public:
-    explicit TreeModelCompleter(QObject *parent = 0);
-    explicit TreeModelCompleter(QAbstractItemModel *model, QObject *parent = 0);
+    explicit TreeModelCompleter(QObject *parent = nullptr);
+    explicit TreeModelCompleter(QAbstractItemModel *model, QObject *parent = nullptr);
 
     QString separator() const;
 public slots:
diff --git a/examples/widgets/tools/undo/commands.cpp b/examples/widgets/tools/undo/commands.cpp
index 81561d2421..97204f9d2f 100644
--- a/examples/widgets/tools/undo/commands.cpp
+++ b/examples/widgets/tools/undo/commands.cpp
@@ -50,18 +50,16 @@
 
 #include "commands.h"
 
-static const int setShapeRectCommandId = 1;
-static const int setShapeColorCommandId = 2;
+static constexpr int setShapeRectCommandId = 1;
+static constexpr int setShapeColorCommandId = 2;
 
 /******************************************************************************
 ** AddShapeCommand
 */
 
 AddShapeCommand::AddShapeCommand(Document *doc, const Shape &shape, QUndoCommand *parent)
-    : QUndoCommand(parent)
+    : QUndoCommand(parent), m_doc(doc), m_shape(shape)
 {
-    m_doc = doc;
-    m_shape = shape;
 }
 
 void AddShapeCommand::undo()
@@ -81,13 +79,11 @@ void AddShapeCommand::redo()
 */
 
 RemoveShapeCommand::RemoveShapeCommand(Document *doc, const QString &shapeName,
-                                        QUndoCommand *parent)
-    : QUndoCommand(parent)
+                                       QUndoCommand *parent)
+    : QUndoCommand(parent), m_doc(doc), m_shape(doc->shape(shapeName))
+    , m_shapeName(shapeName)
 {
     setText(QObject::tr("Remove %1").arg(shapeName));
-    m_doc = doc;
-    m_shape = doc->shape(shapeName);
-    m_shapeName = shapeName;
 }
 
 void RemoveShapeCommand::undo()
@@ -105,15 +101,11 @@ void RemoveShapeCommand::redo()
 */
 
 SetShapeColorCommand::SetShapeColorCommand(Document *doc, const QString &shapeName,
-                                            const QColor &color, QUndoCommand *parent)
-    : QUndoCommand(parent)
+                                           const QColor &color, QUndoCommand *parent)
+    : QUndoCommand(parent), m_doc(doc), m_shapeName(shapeName)
+    , m_oldColor(doc->shape(shapeName).color()), m_newColor(color)
 {
     setText(QObject::tr("Set %1's color").arg(shapeName));
-
-    m_doc = doc;
-    m_shapeName = shapeName;
-    m_oldColor = doc->shape(shapeName).color();
-    m_newColor = color;
 }
 
 void SetShapeColorCommand::undo()
@@ -149,15 +141,11 @@ int SetShapeColorCommand::id() const
 */
 
 SetShapeRectCommand::SetShapeRectCommand(Document *doc, const QString &shapeName,
-                                            const QRect &rect, QUndoCommand *parent)
-    : QUndoCommand(parent)
+                                         const QRect &rect, QUndoCommand *parent)
+    : QUndoCommand(parent), m_doc(doc), m_shapeName(shapeName)
+    , m_oldRect(doc->shape(shapeName).rect()), m_newRect(rect)
 {
     setText(QObject::tr("Change %1's geometry").arg(shapeName));
-
-    m_doc = doc;
-    m_shapeName = shapeName;
-    m_oldRect = doc->shape(shapeName).rect();
-    m_newRect = rect;
 }
 
 void SetShapeRectCommand::undo()
diff --git a/examples/widgets/tools/undo/commands.h b/examples/widgets/tools/undo/commands.h
index de3bebd740..ccb550fdd4 100644
--- a/examples/widgets/tools/undo/commands.h
+++ b/examples/widgets/tools/undo/commands.h
@@ -57,7 +57,8 @@
 class AddShapeCommand : public QUndoCommand
 {
 public:
-    AddShapeCommand(Document *doc, const Shape &shape, QUndoCommand *parent = 0);
+    AddShapeCommand(Document *doc, const Shape &shape,
+                    QUndoCommand *parent = nullptr);
     void undo() override;
     void redo() override;
 
@@ -70,7 +71,8 @@ private:
 class RemoveShapeCommand : public QUndoCommand
 {
 public:
-    RemoveShapeCommand(Document *doc, const QString &shapeName, QUndoCommand *parent = 0);
+    RemoveShapeCommand(Document *doc, const QString &shapeName,
+                       QUndoCommand *parent = nullptr);
     void undo() override;
     void redo() override;
 
@@ -83,8 +85,8 @@ private:
 class SetShapeColorCommand : public QUndoCommand
 {
 public:
-    SetShapeColorCommand(Document *doc, const QString &shapeName, const QColor &color,
-                            QUndoCommand *parent = 0);
+    SetShapeColorCommand(Document *doc, const QString &shapeName,
+                         const QColor &color, QUndoCommand *parent = nullptr);
 
     void undo() override;
     void redo() override;
@@ -102,8 +104,8 @@ private:
 class SetShapeRectCommand : public QUndoCommand
 {
 public:
-    SetShapeRectCommand(Document *doc, const QString &shapeName, const QRect &rect,
-                            QUndoCommand *parent = 0);
+    SetShapeRectCommand(Document *doc, const QString &shapeName,
+                        const QRect &rect, QUndoCommand *parent = nullptr);
 
     void undo() override;
     void redo() override;
diff --git a/examples/widgets/tools/undo/document.cpp b/examples/widgets/tools/undo/document.cpp
index 8935f98a7a..2deed83a99 100644
--- a/examples/widgets/tools/undo/document.cpp
+++ b/examples/widgets/tools/undo/document.cpp
@@ -48,14 +48,15 @@
 **
 ****************************************************************************/
 
-#include <qevent.h>
+#include "document.h"
+#include "commands.h"
+
 #include <QPainter>
+#include <QPaintEvent>
 #include <QTextStream>
 #include <QUndoStack>
-#include "document.h"
-#include "commands.h"
 
-static const int resizeHandleWidth = 6;
+static constexpr int resizeHandleWidth = 6;
 
 /******************************************************************************
 ** Shape
@@ -96,26 +97,21 @@ QRect Shape::resizeHandle() const
 
 QString Shape::typeToString(Type type)
 {
-    QString result;
-
     switch (type) {
         case Rectangle:
-            result = QLatin1String("Rectangle");
-            break;
+            return QLatin1String("Rectangle");
         case Circle:
-            result = QLatin1String("Circle");
-            break;
+            return QLatin1String("Circle");
         case Triangle:
-            result = QLatin1String("Triangle");
-            break;
+            return QLatin1String("Triangle");
     }
 
-    return result;
+    return QString();
 }
 
 Shape::Type Shape::stringToType(const QString &s, bool *ok)
 {
-    if (ok != 0)
+    if (ok != nullptr)
         *ok = true;
 
     if (s == QLatin1String("Rectangle"))
@@ -125,7 +121,7 @@ Shape::Type Shape::stringToType(const QString &s, bool *ok)
     if (s == QLatin1String("Triangle"))
         return Triangle;
 
-    if (ok != 0)
+    if (ok != nullptr)
         *ok = false;
     return Rectangle;
 }
@@ -135,10 +131,8 @@ Shape::Type Shape::stringToType(const QString &s, bool *ok)
 */
 
 Document::Document(QWidget *parent)
-    : QWidget(parent), m_currentIndex(-1), m_mousePressIndex(-1), m_resizeHandlePressed(false)
+    : QWidget(parent), m_undoStack(new QUndoStack(this))
 {
-    m_undoStack = new QUndoStack(this);
-
     setAutoFillBackground(true);
     setBackgroundRole(QPalette::Base);
 
diff --git a/examples/widgets/tools/undo/document.h b/examples/widgets/tools/undo/document.h
index 8076d7185c..01447ef541 100644
--- a/examples/widgets/tools/undo/document.h
+++ b/examples/widgets/tools/undo/document.h
@@ -70,7 +70,7 @@ public:
     QColor color() const;
 
     static QString typeToString(Type type);
-    static Type stringToType(const QString &s, bool *ok = 0);
+    static Type stringToType(const QString &s, bool *ok = nullptr);
 
     static const QSize minSize;
 
@@ -88,7 +88,7 @@ class Document : public QWidget
     Q_OBJECT
 
 public:
-    Document(QWidget *parent = 0);
+    Document(QWidget *parent = nullptr);
 
     QString addShape(const Shape &shape);
     void deleteShape(const QString &shapeName);
@@ -121,14 +121,13 @@ private:
     int indexAt(const QPoint &pos) const;
     QString uniqueName(const QString &name) const;
 
-    QList<Shape> m_shapeList;
-    int m_currentIndex;
-    int m_mousePressIndex;
+    QVector<Shape> m_shapeList;
     QPoint m_mousePressOffset;
-    bool m_resizeHandlePressed;
     QString m_fileName;
-
-    QUndoStack *m_undoStack;
+    QUndoStack *m_undoStack = nullptr;
+    int m_currentIndex = -1;
+    int m_mousePressIndex = -1;
+    bool m_resizeHandlePressed = false;
 };
 
 #endif // DOCUMENT_H
diff --git a/examples/widgets/tools/undo/mainwindow.cpp b/examples/widgets/tools/undo/mainwindow.cpp
index 118d604742..9d83e3067a 100644
--- a/examples/widgets/tools/undo/mainwindow.cpp
+++ b/examples/widgets/tools/undo/mainwindow.cpp
@@ -48,6 +48,10 @@
 **
 ****************************************************************************/
 
+#include "mainwindow.h"
+#include "document.h"
+#include "commands.h"
+
 #include <QUndoGroup>
 #include <QUndoStack>
 #include <QFileDialog>
@@ -55,9 +59,6 @@
 #include <QRandomGenerator>
 #include <QTextStream>
 #include <QToolButton>
-#include "document.h"
-#include "mainwindow.h"
-#include "commands.h"
 
 MainWindow::MainWindow(QWidget *parent)
     : QMainWindow(parent)
@@ -122,17 +123,17 @@ MainWindow::MainWindow(QWidget *parent)
 void MainWindow::updateActions()
 {
     Document *doc = currentDocument();
-    m_undoGroup->setActiveStack(doc == 0 ? 0 : doc->undoStack());
-    QString shapeName = doc == 0 ? QString() : doc->currentShapeName();
-
-    actionAddRobot->setEnabled(doc != 0);
-    actionAddSnowman->setEnabled(doc != 0);
-    actionAddCircle->setEnabled(doc != 0);
-    actionAddRectangle->setEnabled(doc != 0);
-    actionAddTriangle->setEnabled(doc != 0);
-    actionClose->setEnabled(doc != 0);
-    actionSave->setEnabled(doc != 0 && !doc->undoStack()->isClean());
-    undoLimit->setEnabled(doc != 0 && doc->undoStack()->count() == 0);
+    m_undoGroup->setActiveStack(doc == nullptr ? nullptr : doc->undoStack());
+    QString shapeName = doc == nullptr ? QString() : doc->currentShapeName();
+
+    actionAddRobot->setEnabled(doc != nullptr);
+    actionAddSnowman->setEnabled(doc != nullptr);
+    actionAddCircle->setEnabled(doc != nullptr);
+    actionAddRectangle->setEnabled(doc != nullptr);
+    actionAddTriangle->setEnabled(doc != nullptr);
+    actionClose->setEnabled(doc != nullptr);
+    actionSave->setEnabled(doc != nullptr && !doc->undoStack()->isClean());
+    undoLimit->setEnabled(doc != nullptr && doc->undoStack()->count() == 0);
 
     if (shapeName.isEmpty()) {
         actionRed->setEnabled(false);
@@ -147,7 +148,7 @@ void MainWindow::updateActions()
         actionRemoveShape->setEnabled(true);
     }
 
-    if (doc != 0) {
+    if (doc != nullptr) {
         int index = documentTabs->indexOf(doc);
         Q_ASSERT(index != -1);
         static const QIcon unsavedIcon(":/icons/filesave.png");
@@ -264,7 +265,7 @@ void MainWindow::removeDocument(Document *doc)
 void MainWindow::saveDocument()
 {
     Document *doc = currentDocument();
-    if (doc == 0)
+    if (doc == nullptr)
         return;
 
     for (;;) {
@@ -298,7 +299,7 @@ void MainWindow::saveDocument()
 void MainWindow::closeDocument()
 {
     Document *doc = currentDocument();
-    if (doc == 0)
+    if (doc == nullptr)
         return;
 
     if (!doc->undoStack()->isClean()) {
@@ -338,10 +339,10 @@ static QRect randomRect(const QSize &s)
 {
     QSize min = Shape::minSize;
 
-    int left = (int) ((0.0 + s.width() - min.width())*(QRandomGenerator::global()->bounded(1.0)));
-    int top = (int) ((0.0 + s.height() - min.height())*(QRandomGenerator::global()->bounded(1.0)));
-    int width = (int) ((0.0 + s.width() - left - min.width())*(QRandomGenerator::global()->bounded(1.0))) + min.width();
-    int height = (int) ((0.0 + s.height() - top - min.height())*(QRandomGenerator::global()->bounded(1.0))) + min.height();
+    int left = qRound((s.width() - min.width()) * (QRandomGenerator::global()->bounded(1.0)));
+    int top = qRound((s.height() - min.height()) * (QRandomGenerator::global()->bounded(1.0)));
+    int width = qRound((s.width() - left - min.width()) * (QRandomGenerator::global()->bounded(1.0))) + min.width();
+    int height = qRound((s.height() - top - min.height()) * (QRandomGenerator::global()->bounded(1.0))) + min.height();
 
     return QRect(left, top, width, height);
 }
@@ -349,7 +350,7 @@ static QRect randomRect(const QSize &s)
 void MainWindow::addShape()
 {
     Document *doc = currentDocument();
-    if (doc == 0)
+    if (doc == nullptr)
         return;
 
     Shape::Type type;
@@ -369,7 +370,7 @@ void MainWindow::addShape()
 void MainWindow::removeShape()
 {
     Document *doc = currentDocument();
-    if (doc == 0)
+    if (doc == nullptr)
         return;
 
     QString shapeName = doc->currentShapeName();
@@ -382,7 +383,7 @@ void MainWindow::removeShape()
 void MainWindow::setShapeColor()
 {
     Document *doc = currentDocument();
-    if (doc == 0)
+    if (doc == nullptr)
         return;
 
     QString shapeName = doc->currentShapeName();
@@ -409,7 +410,7 @@ void MainWindow::setShapeColor()
 void MainWindow::addSnowman()
 {
     Document *doc = currentDocument();
-    if (doc == 0)
+    if (doc == nullptr)
         return;
 
     // Create a macro command using beginMacro() and endMacro()
@@ -427,7 +428,7 @@ void MainWindow::addSnowman()
 void MainWindow::addRobot()
 {
     Document *doc = currentDocument();
-    if (doc == 0)
+    if (doc == nullptr)
         return;
 
     // Compose a macro command by explicitly adding children to a parent command
diff --git a/examples/widgets/tools/undo/mainwindow.h b/examples/widgets/tools/undo/mainwindow.h
index 57c1f87ab2..87ee3084fb 100644
--- a/examples/widgets/tools/undo/mainwindow.h
+++ b/examples/widgets/tools/undo/mainwindow.h
@@ -61,7 +61,7 @@ class MainWindow : public QMainWindow, public Ui::MainWindow
     Q_OBJECT
 
 public:
-    MainWindow(QWidget *parent = 0);
+    MainWindow(QWidget *parent = nullptr);
 
     void addDocument(Document *doc);
     void removeDocument(Document *doc);
diff --git a/examples/widgets/tools/undoframework/commands.cpp b/examples/widgets/tools/undoframework/commands.cpp
index c3e7383de1..077d7eccaa 100644
--- a/examples/widgets/tools/undoframework/commands.cpp
+++ b/examples/widgets/tools/undoframework/commands.cpp
@@ -48,19 +48,17 @@
 **
 ****************************************************************************/
 
-#include <QtWidgets>
-
 #include "commands.h"
 #include "diagramitem.h"
 
+#include <QGraphicsScene>
+
 //! [0]
 MoveCommand::MoveCommand(DiagramItem *diagramItem, const QPointF &oldPos,
-                 QUndoCommand *parent)
-    : QUndoCommand(parent)
+                         QUndoCommand *parent)
+    : QUndoCommand(parent), myDiagramItem(diagramItem)
+    , myOldPos(oldPos), newPos(diagramItem->pos())
 {
-    myDiagramItem = diagramItem;
-    newPos = diagramItem->pos();
-    myOldPos = oldPos;
 }
 //! [0]
 
@@ -71,7 +69,7 @@ bool MoveCommand::mergeWith(const QUndoCommand *command)
     DiagramItem *item = moveCommand->myDiagramItem;
 
     if (myDiagramItem != item)
-    return false;
+        return false;
 
     newPos = item->pos();
     setText(QObject::tr("Move %1")
@@ -102,9 +100,8 @@ void MoveCommand::redo()
 
 //! [4]
 DeleteCommand::DeleteCommand(QGraphicsScene *scene, QUndoCommand *parent)
-    : QUndoCommand(parent)
+    : QUndoCommand(parent), myGraphicsScene(scene)
 {
-    myGraphicsScene = scene;
     QList<QGraphicsItem *> list = myGraphicsScene->selectedItems();
     list.first()->setSelected(false);
     myDiagramItem = static_cast<DiagramItem *>(list.first());
@@ -131,11 +128,10 @@ void DeleteCommand::redo()
 //! [7]
 AddCommand::AddCommand(DiagramItem::DiagramType addType,
                        QGraphicsScene *scene, QUndoCommand *parent)
-    : QUndoCommand(parent)
+    : QUndoCommand(parent), myGraphicsScene(scene)
 {
     static int itemCount = 0;
 
-    myGraphicsScene = scene;
     myDiagramItem = new DiagramItem(addType);
     initialPosition = QPointF((itemCount * 15) % int(scene->width()),
                               (itemCount * 15) % int(scene->height()));
diff --git a/examples/widgets/tools/undoframework/commands.h b/examples/widgets/tools/undoframework/commands.h
index dc53c14557..185d36d668 100644
--- a/examples/widgets/tools/undoframework/commands.h
+++ b/examples/widgets/tools/undoframework/commands.h
@@ -62,7 +62,7 @@ public:
     enum { Id = 1234 };
 
     MoveCommand(DiagramItem *diagramItem, const QPointF &oldPos,
-                QUndoCommand *parent = 0);
+                QUndoCommand *parent = nullptr);
 
     void undo() override;
     void redo() override;
@@ -80,7 +80,7 @@ private:
 class DeleteCommand : public QUndoCommand
 {
 public:
-    explicit DeleteCommand(QGraphicsScene *graphicsScene, QUndoCommand *parent = 0);
+    explicit DeleteCommand(QGraphicsScene *graphicsScene, QUndoCommand *parent = nullptr);
 
     void undo() override;
     void redo() override;
@@ -96,7 +96,7 @@ class AddCommand : public QUndoCommand
 {
 public:
     AddCommand(DiagramItem::DiagramType addType, QGraphicsScene *graphicsScene,
-               QUndoCommand *parent = 0);
+               QUndoCommand *parent = nullptr);
     ~AddCommand();
 
     void undo() override;
diff --git a/examples/widgets/tools/undoframework/diagramitem.cpp b/examples/widgets/tools/undoframework/diagramitem.cpp
index 723645c9b2..91da6538cf 100644
--- a/examples/widgets/tools/undoframework/diagramitem.cpp
+++ b/examples/widgets/tools/undoframework/diagramitem.cpp
@@ -48,10 +48,11 @@
 **
 ****************************************************************************/
 
-#include <QtWidgets>
-
 #include "diagramitem.h"
 
+#include <QBrush>
+#include <QRandomGenerator>
+
 DiagramItem::DiagramItem(DiagramType diagramType, QGraphicsItem *item)
     : QGraphicsPolygonItem(item)
 {
@@ -65,7 +66,9 @@ DiagramItem::DiagramItem(DiagramType diagramType, QGraphicsItem *item)
         setPolygon(trianglePolygon);
     }
 
-    QColor color(QRandomGenerator::global()->bounded(256), QRandomGenerator::global()->bounded(256), QRandomGenerator::global()->bounded(256));
+    QColor color(QRandomGenerator::global()->bounded(256),
+                 QRandomGenerator::global()->bounded(256),
+                 QRandomGenerator::global()->bounded(256));
     QBrush brush(color);
     setBrush(brush);
     setFlag(QGraphicsItem::ItemIsSelectable);
diff --git a/examples/widgets/tools/undoframework/diagramitem.h b/examples/widgets/tools/undoframework/diagramitem.h
index 1638dcbea8..13ff614427 100644
--- a/examples/widgets/tools/undoframework/diagramitem.h
+++ b/examples/widgets/tools/undoframework/diagramitem.h
@@ -66,9 +66,10 @@ public:
     enum { Type = UserType + 1 };
     enum DiagramType { Box, Triangle };
 
-    explicit DiagramItem(DiagramType diagramType, QGraphicsItem *item = 0);
+    explicit DiagramItem(DiagramType diagramType, QGraphicsItem *item = nullptr);
 
-    DiagramType diagramType() const {
+    DiagramType diagramType() const
+    {
         return polygon() == boxPolygon ? Box : Triangle;
     }
     int type() const override { return Type; }
diff --git a/examples/widgets/tools/undoframework/diagramscene.cpp b/examples/widgets/tools/undoframework/diagramscene.cpp
index 63aad97cb1..65909ab6cb 100644
--- a/examples/widgets/tools/undoframework/diagramscene.cpp
+++ b/examples/widgets/tools/undoframework/diagramscene.cpp
@@ -48,27 +48,24 @@
 **
 ****************************************************************************/
 
-#include <QtWidgets>
-
 #include "diagramscene.h"
 #include "diagramitem.h"
 
+#include <QGraphicsSceneMouseEvent>
+
 DiagramScene::DiagramScene(QObject *parent)
     : QGraphicsScene(parent)
-{
-    movingItem = 0;
-}
+{}
 
 void DiagramScene::mousePressEvent(QGraphicsSceneMouseEvent *event)
 {
     QPointF mousePos(event->buttonDownScenePos(Qt::LeftButton).x(),
                      event->buttonDownScenePos(Qt::LeftButton).y());
     const QList<QGraphicsItem *> itemList = items(mousePos);
-    movingItem = itemList.isEmpty() ? 0 : itemList.first();
+    movingItem = itemList.isEmpty() ? nullptr : itemList.first();
 
-    if (movingItem != 0 && event->button() == Qt::LeftButton) {
+    if (movingItem != nullptr && event->button() == Qt::LeftButton)
         oldPos = movingItem->pos();
-    }
 
     clearSelection();
     QGraphicsScene::mousePressEvent(event);
@@ -76,11 +73,11 @@ void DiagramScene::mousePressEvent(QGraphicsSceneMouseEvent *event)
 
 void DiagramScene::mouseReleaseEvent(QGraphicsSceneMouseEvent *event)
 {
-    if (movingItem != 0 && event->button() == Qt::LeftButton) {
+    if (movingItem != nullptr && event->button() == Qt::LeftButton) {
         if (oldPos != movingItem->pos())
             emit itemMoved(qgraphicsitem_cast<DiagramItem *>(movingItem),
                            oldPos);
-        movingItem = 0;
+        movingItem = nullptr;
     }
     QGraphicsScene::mouseReleaseEvent(event);
 }
diff --git a/examples/widgets/tools/undoframework/diagramscene.h b/examples/widgets/tools/undoframework/diagramscene.h
index b1e2804ba6..205d4162bb 100644
--- a/examples/widgets/tools/undoframework/diagramscene.h
+++ b/examples/widgets/tools/undoframework/diagramscene.h
@@ -66,7 +66,7 @@ class DiagramScene : public QGraphicsScene
     Q_OBJECT
 
 public:
-    DiagramScene(QObject *parent = 0);
+    DiagramScene(QObject *parent = nullptr);
 
 signals:
     void itemMoved(DiagramItem *movedItem, const QPointF &movedFromPosition);
@@ -76,7 +76,7 @@ protected:
     void mouseReleaseEvent(QGraphicsSceneMouseEvent *event) override;
 
 private:
-    QGraphicsItem *movingItem;
+    QGraphicsItem *movingItem = nullptr;
     QPointF oldPos;
 };
 //! [0]
diff --git a/examples/widgets/tools/undoframework/main.cpp b/examples/widgets/tools/undoframework/main.cpp
index 51fb5c53eb..cf090f56eb 100644
--- a/examples/widgets/tools/undoframework/main.cpp
+++ b/examples/widgets/tools/undoframework/main.cpp
@@ -48,7 +48,7 @@
 **
 ****************************************************************************/
 
-#include <QtWidgets>
+#include <QApplication>
 
 #include "mainwindow.h"
 
diff --git a/examples/widgets/tools/undoframework/mainwindow.cpp b/examples/widgets/tools/undoframework/mainwindow.cpp
index e95d50d164..583af11a2b 100644
--- a/examples/widgets/tools/undoframework/mainwindow.cpp
+++ b/examples/widgets/tools/undoframework/mainwindow.cpp
@@ -48,13 +48,18 @@
 **
 ****************************************************************************/
 
-#include <QtWidgets>
-
 #include "mainwindow.h"
 #include "diagramscene.h"
 #include "diagramitem.h"
 #include "commands.h"
 
+#include <QAction>
+#include <QGraphicsView>
+#include <QMenu>
+#include <QMenuBar>
+#include <QMessageBox>
+#include <QUndoView>
+
 //! [0]
 MainWindow::MainWindow()
 {
diff --git a/examples/widgets/tools/undoframework/mainwindow.h b/examples/widgets/tools/undoframework/mainwindow.h
index def2b7d789..c1a56e0770 100644
--- a/examples/widgets/tools/undoframework/mainwindow.h
+++ b/examples/widgets/tools/undoframework/mainwindow.h
@@ -87,22 +87,22 @@ private:
     void createMenus();
     void createUndoView();
 
-    QAction *deleteAction;
-    QAction *addBoxAction;
-    QAction *addTriangleAction;
-    QAction *undoAction;
-    QAction *redoAction;
-    QAction *exitAction;
-    QAction *aboutAction;
+    QAction *deleteAction = nullptr;
+    QAction *addBoxAction = nullptr;
+    QAction *addTriangleAction = nullptr;
+    QAction *undoAction = nullptr;
+    QAction *redoAction = nullptr;
+    QAction *exitAction = nullptr;
+    QAction *aboutAction = nullptr;
 
-    QMenu *fileMenu;
-    QMenu *editMenu;
-    QMenu *itemMenu;
-    QMenu *helpMenu;
+    QMenu *fileMenu = nullptr;
+    QMenu *editMenu = nullptr;
+    QMenu *itemMenu = nullptr;
+    QMenu *helpMenu = nullptr;
 
-    DiagramScene *diagramScene;
-    QUndoStack *undoStack;
-    QUndoView *undoView;
+    DiagramScene *diagramScene = nullptr;
+    QUndoStack *undoStack = nullptr;
+    QUndoView *undoView = nullptr;
 };
 //! [0]