Deprecate QGuiApplication::paletteChanged() signal

Rather than have a paletteChanged() signal which can be connected to for
tracking when the application palette has changed, then it is better to
use the event that is sent to all windows and the application itself.
That way it is easy for a window/widget or item that cares about the
change to the application font to catch it in the event() function.

[ChangeLog][QtGui][QGuiApplication] Deprecated paletteChanged() signal
in favor of QEvent::ApplicationPaletteChanged.

Change-Id: I95da211e30590e357007cc14d8ee266baceba7b3
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/gui/kernel/qguiapplication.cpp

@@ -1900,10 +1900,11 @@ bool QGuiApplication::event(QEvent *e)
             if (topLevelWindow->flags() != Qt::Desktop)
                 postEvent(topLevelWindow, new QEvent(QEvent::LanguageChange));
         }
-    } else if (e->type() == QEvent::ApplicationFontChange) {
+    } else if (e->type() == QEvent::ApplicationFontChange ||
+               e->type() == QEvent::ApplicationPaletteChange) {
         for (auto *topLevelWindow : QGuiApplication::topLevelWindows()) {
             if (topLevelWindow->flags() != Qt::Desktop)
-                postEvent(topLevelWindow, new QEvent(QEvent::ApplicationFontChange));
+                postEvent(topLevelWindow, new QEvent(e->type()));
         }
     } else if (e->type() == QEvent::Quit) {
         // Close open windows. This is done in order to deliver de-expose
@@ -3271,8 +3272,10 @@ QClipboard * QGuiApplication::clipboard()
 /*!
     \since 5.4
     \fn void QGuiApplication::paletteChanged(const QPalette &palette)
+    \obsolete
 
-    This signal is emitted when the \a palette of the application changes.
+    This signal is emitted when the \a palette of the application changes. Use
+    QEvent::ApplicationPaletteChanged instead.
 
     \sa palette()
 */

src/gui/kernel/qguiapplication.h

@@ -188,9 +188,9 @@ Q_SIGNALS:
     void commitDataRequest(QSessionManager &sessionManager);
     void saveStateRequest(QSessionManager &sessionManager);
 #endif
-    void paletteChanged(const QPalette &pal);
     void applicationDisplayNameChanged();
 #if QT_DEPRECATED_SINCE(6, 0)
+    void paletteChanged(const QPalette &pal);
     void fontChanged(const QFont &font);
 #endif
 protected:

src/widgets/kernel/qapplication.cpp

@@ -1211,18 +1211,15 @@ void QApplicationPrivate::handlePaletteChanged(const char *className)
 
     // Setting the global application palette is documented to
     // reset any previously set class specific widget palettes.
-    bool sendPaletteChangeToAllWidgets = false;
+    if (!className && !widgetPalettes.isEmpty())
-    if (!className && !widgetPalettes.isEmpty()) {
-        sendPaletteChangeToAllWidgets = true;
         widgetPalettes.clear();
-    }
 
     QGuiApplicationPrivate::handlePaletteChanged(className);
 
     QEvent event(QEvent::ApplicationPaletteChange);
     const QWidgetList widgets = QApplication::allWidgets();
     for (auto widget : widgets) {
-        if (sendPaletteChangeToAllWidgets || (!className && widget->isWindow()) || (className && widget->inherits(className)))
+        if (!widget->isWindow() && widget->inherits(className))
             QCoreApplication::sendEvent(widget, &event);
     }
 
@@ -1734,7 +1731,8 @@ bool QApplication::event(QEvent *e)
 #endif
     }
 
-    if (e->type() == QEvent::LanguageChange || e->type() == QEvent::ApplicationFontChange) {
+    if (e->type() == QEvent::LanguageChange || e->type() == QEvent::ApplicationFontChange ||
+        e->type() == QEvent::ApplicationPaletteChange) {
         // QGuiApplication::event does not account for the cases where
         // there is a top level widget without a window handle. So they
         // need to have the event posted here

tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp

@@ -418,6 +418,7 @@ private slots:
     void winIdAfterClose();
     void receivesLanguageChangeEvent();
     void receivesApplicationFontChangeEvent();
+    void receivesApplicationPaletteChangeEvent();
 
 private:
     bool ensureScreenSize(int width, int height);
@@ -4988,6 +4989,7 @@ void tst_QWidget::isOpaque()
         QVERIFY(!::isOpaque(&widget));
 
         QApplication::setPalette(old);
+        QApplication::sendPostedEvents(&widget, QEvent::ApplicationPaletteChange);
         QCOMPARE(::isOpaque(&widget), old.color(QPalette::Window).alpha() == 255);
     }
 #endif
@@ -11662,6 +11664,7 @@ public:
     ChangeEventWidget(QWidget *parent = nullptr) : QWidget(parent) {}
     int languageChangeCount = 0;
     int applicationFontChangeCount = 0;
+    int applicationPaletteChangeCount = 0;
 protected:
     bool event(QEvent *e) override
     {
@@ -11669,6 +11672,8 @@ protected:
             languageChangeCount++;
         else if (e->type() == QEvent::ApplicationFontChange)
             applicationFontChangeCount++;
+        else if (e->type() == QEvent::ApplicationPaletteChange)
+            applicationPaletteChangeCount++;
         return QWidget::event(e);
     }
 };
@@ -11679,6 +11684,7 @@ public:
     ChangeEventWindow(QWindow *parent = nullptr) : QWindow(parent) {}
     int languageChangeCount = 0;
     int applicationFontChangeCount = 0;
+    int applicationPaletteChangeCount = 0;
 protected:
     bool event(QEvent *e) override
     {
@@ -11686,6 +11692,8 @@ protected:
             languageChangeCount++;
         else if (e->type() == QEvent::ApplicationFontChange)
             applicationFontChangeCount++;
+        else if (e->type() == QEvent::ApplicationPaletteChange)
+            applicationPaletteChangeCount++;
         return QWindow::event(e);
     }
 };
@@ -11739,5 +11747,32 @@ void tst_QWidget::receivesApplicationFontChangeEvent()
     QApplication::setFont(origFont);
 }
 
+void tst_QWidget::receivesApplicationPaletteChangeEvent()
+{
+    // Confirm that any QWindow or top level QWidget only gets a single
+    // ApplicationPaletteChange event when the font is changed
+    const QPalette origPalette = QApplication::palette();
+
+    ChangeEventWidget topLevel;
+    auto childWidget = new ChangeEventWidget(&topLevel);
+    topLevel.show();
+    QVERIFY(QTest::qWaitForWindowExposed(&topLevel));
+    ChangeEventWindow ww;
+    ww.show();
+    QVERIFY(QTest::qWaitForWindowExposed(&ww));
+    ChangeEventWidget topLevelNotShown;
+    QPalette changedPalette = origPalette;
+    changedPalette.setColor(QPalette::Base, Qt::red);
+    QApplication::setPalette(changedPalette);
+    QCoreApplication::sendPostedEvents(0, QEvent::ApplicationPaletteChange);
+    QCOMPARE(topLevel.applicationPaletteChangeCount, 1);
+    QCOMPARE(topLevelNotShown.applicationPaletteChangeCount, 1);
+    // QWidget should not be passing the event on automatically
+    QCOMPARE(childWidget->applicationPaletteChangeCount, 0);
+    QCOMPARE(ww.applicationPaletteChangeCount, 1);
+
+    QApplication::setPalette(origPalette);
+}
+
 QTEST_MAIN(tst_QWidget)
 #include "tst_qwidget.moc"