examples/: compile with QT_NO_CONTEXTLESS_CONNECT

Examples are usually a good way to get to know a new codebase, do not
teach developers who are new to Qt about the 3-arg connect() to begin
with.

Drive-by changes:
- `this` can't be implicitly captured with [=] in a lambda, instead
  capture by reference
- Update docs related to the sqlbrowser example; the overloaded signal
  it mentions has been removed in Qt6
- In the sqlbrowser example, rename addConnection() (no-arg) overload to
  openNewConnectionDialog, suggested in code review

Change-Id: I30c9f35bda4ac2f460d767ab7f84422ae3ed09f7
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

examples/CMakeLists.txt

@@ -3,6 +3,8 @@
 
 qt_examples_build_begin(EXTERNAL_BUILD)
 
+add_compile_definitions(QT_NO_CONTEXTLESS_CONNECT)
+
 add_subdirectory(corelib)
 add_subdirectory(embedded)
 if(TARGET Qt6::DBus)

examples/corelib/bindableproperties/bindablesubscription/main.cpp

@@ -28,29 +28,29 @@ int main(int argc, char *argv[])
 
     // Initialize subscription data
     QRadioButton *monthly = w.findChild<QRadioButton *>("btnMonthly");
-    QObject::connect(monthly, &QRadioButton::clicked, [&] {
+    QObject::connect(monthly, &QRadioButton::clicked, monthly, [&] {
         subscription.setDuration(BindableSubscription::Monthly);
     });
     QRadioButton *quarterly = w.findChild<QRadioButton *>("btnQuarterly");
-    QObject::connect(quarterly, &QRadioButton::clicked, [&] {
+    QObject::connect(quarterly, &QRadioButton::clicked, quarterly, [&] {
         subscription.setDuration(BindableSubscription::Quarterly);
     });
     QRadioButton *yearly = w.findChild<QRadioButton *>("btnYearly");
-    QObject::connect(yearly, &QRadioButton::clicked, [&] {
+    QObject::connect(yearly, &QRadioButton::clicked, yearly, [&] {
         subscription.setDuration(BindableSubscription::Yearly);
     });
 
     // Initialize user data
     QPushButton *germany = w.findChild<QPushButton *>("btnGermany");
-    QObject::connect(germany, &QPushButton::clicked, [&] {
+    QObject::connect(germany, &QPushButton::clicked, germany, [&] {
         user.setCountry(BindableUser::Country::Germany);
     });
     QPushButton *finland = w.findChild<QPushButton *>("btnFinland");
-    QObject::connect(finland, &QPushButton::clicked, [&] {
+    QObject::connect(finland, &QPushButton::clicked, finland, [&] {
         user.setCountry(BindableUser::Country::Finland);
     });
     QPushButton *norway = w.findChild<QPushButton *>("btnNorway");
-    QObject::connect(norway, &QPushButton::clicked, [&] {
+    QObject::connect(norway, &QPushButton::clicked, norway, [&] {
         user.setCountry(BindableUser::Country::Norway);
     });
 

examples/corelib/bindableproperties/subscription/main.cpp

@@ -64,25 +64,25 @@ int main(int argc, char *argv[])
     // Track the price changes
 
 //! [connect-price-changed]
-    QObject::connect(&subscription, &Subscription::priceChanged, [&] {
+    QObject::connect(&subscription, &Subscription::priceChanged, priceDisplay, [&] {
         QLocale lc{QLocale::AnyLanguage, user.country()};
         priceDisplay->setText(lc.toCurrencyString(subscription.price() / subscription.duration()));
     });
 //! [connect-price-changed]
 
 //! [connect-validity-changed]
-    QObject::connect(&subscription, &Subscription::isValidChanged, [&] {
+    QObject::connect(&subscription, &Subscription::isValidChanged, priceDisplay, [&] {
         priceDisplay->setEnabled(subscription.isValid());
     });
 //! [connect-validity-changed]
 
 //! [connect-user]
-    QObject::connect(&user, &User::countryChanged, [&] {
+    QObject::connect(&user, &User::countryChanged, &subscription, [&] {
         subscription.calculatePrice();
         subscription.updateValidity();
     });
 
-    QObject::connect(&user, &User::ageChanged, [&] {
+    QObject::connect(&user, &User::ageChanged, &subscription, [&] {
         subscription.updateValidity();
     });
 //! [connect-user]

examples/sql/doc/src/drilldown.qdoc

@@ -154,10 +154,6 @@
     We need to use lambdas for connecting the \c enableButtons slot
     because its signature does not match \c QTextEdit::textChanged
     and \c QComboBox::currentIndexChanged.
-    Since the latter has another overload with the signature
-    \c {const QString &} and the selected signal would be ambiguous,
-    we need to use \c QOverload<int>::of to select a specific overload
-    for \c currentIndexChanged.
 
     We add all the widgets into a layout, store the item ID and the
     name of the displayed image file for future reference, and set

examples/sql/drilldown/informationwindow.cpp

@@ -37,12 +37,8 @@ InformationWindow::InformationWindow(int id, QSqlRelationalTableModel *items,
 //! [3]
 
 //! [4]
-    connect(descriptionEditor, &QTextEdit::textChanged, [=]() {
-        enableButtons();
-    });
-    connect(imageFileEditor, &QComboBox::currentIndexChanged, [=]() {
-        enableButtons();
-    });
+    connect(descriptionEditor, &QTextEdit::textChanged, this, [this]() { enableButtons(); });
+    connect(imageFileEditor, &QComboBox::currentIndexChanged, this, [this]() { enableButtons(); });
 
     QFormLayout *formLayout = new QFormLayout;
     formLayout->addRow(itemLabel, itemText);

examples/sql/sqlbrowser/browser.cpp

@@ -71,7 +71,7 @@ QSqlError Browser::addConnection(const QString &driver, const QString &dbName, c
     return err;
 }
 
-void Browser::addConnection()
+void Browser::openNewConnectionDialog()
 {
     QSqlConnectionDialog dialog(this);
     if (dialog.exec() != QDialog::Accepted)

examples/sql/sqlbrowser/browser.h

@@ -32,7 +32,7 @@ public slots:
     void exec();
     void showTable(const QString &table);
     void showMetaData(const QString &table);
-    void addConnection();
+    void openNewConnectionDialog();
     void currentChanged() { updateActions(); }
     void about();
 

examples/sql/sqlbrowser/main.cpp

@@ -33,18 +33,17 @@ int main(int argc, char *argv[])
     mainWin.setCentralWidget(&browser);
 
     QMenu *fileMenu = mainWin.menuBar()->addMenu(QObject::tr("&File"));
-    fileMenu->addAction(QObject::tr("Add &Connection..."),
-            [&]() { browser.addConnection(); });
+    fileMenu->addAction(QObject::tr("Add &Connection..."), &browser,
+                        &Browser::openNewConnectionDialog);
     fileMenu->addSeparator();
-    fileMenu->addAction(QObject::tr("&Quit"), []() { qApp->quit(); });
+    fileMenu->addAction(QObject::tr("&Quit"), qApp, &QApplication::quit);
 
     QMenu *helpMenu = mainWin.menuBar()->addMenu(QObject::tr("&Help"));
-    helpMenu->addAction(QObject::tr("About"), [&]() { browser.about(); });
-    helpMenu->addAction(QObject::tr("About Qt"), []() { qApp->aboutQt(); });
+    helpMenu->addAction(QObject::tr("About"), &browser, &Browser::about);
+    helpMenu->addAction(QObject::tr("About Qt"), qApp, &QApplication::aboutQt);
 
-    QObject::connect(&browser, &Browser::statusMessage, [&mainWin](const QString &text) {
-        mainWin.statusBar()->showMessage(text);
-    });
+    QObject::connect(&browser, &Browser::statusMessage, &mainWin,
+                     [&mainWin](const QString &text) { mainWin.statusBar()->showMessage(text); });
 
     addConnectionsFromCommandline(app.arguments(), &browser);
     mainWin.show();

examples/vulkan/hellovulkancubes/renderer.cpp

@@ -38,7 +38,7 @@ Renderer::Renderer(VulkanWindow *w, int initialCount)
     m_blockMesh.load(QStringLiteral(":/block.buf"));
     m_logoMesh.load(QStringLiteral(":/qt_logo.buf"));
 
-    QObject::connect(&m_frameWatcher, &QFutureWatcherBase::finished, [this] {
+    QObject::connect(&m_frameWatcher, &QFutureWatcherBase::finished, m_window, [this] {
         if (m_framePending) {
             m_framePending = false;
             m_window->frameReady();