QGuiApplication: Add fontChanged signal

This removes the need to install an event filter on qApp just for this.
A similar thing was done with setPalette to reduce the number of event filters
in e.g. SystemPalette and Quick Controls.

[ChangeLog][QtGui][QGuiApplication] Added fontChanged signal

Change-Id: Ifa843aa42b91ac63ab17c3b064ac0e764aac77d3
Reviewed-by: J-P Nurmi <jpnurmi@qt.io>

3 files changed, 41 insertions, 0 deletions

diff --git a/src/gui/kernel/qguiapplication.cpp b/src/gui/kernel/qguiapplication.cpp
index 8149fa3905..3d85f47f34 100644
--- a/src/gui/kernel/qguiapplication.cpp
+++ b/src/gui/kernel/qguiapplication.cpp
@@ -3110,6 +3110,15 @@ void QGuiApplicationPrivate::applyWindowGeometrySpecificationTo(QWindow *window)
 }
 
 /*!
+    \since 5.11
+    \fn void QGuiApplication::fontChanged(const QFont &font)
+
+    This signal is emitted when the \a font of the application changes.
+
+    \sa font()
+*/
+
+/*!
     Returns the default application font.
 
     \sa setFont()
@@ -3130,11 +3139,16 @@ QFont QGuiApplication::font()
 void QGuiApplication::setFont(const QFont &font)
 {
     QMutexLocker locker(&applicationFontMutex);
+    const bool emitChange = !QGuiApplicationPrivate::app_font
+                            || (*QGuiApplicationPrivate::app_font != font);
     if (!QGuiApplicationPrivate::app_font)
         QGuiApplicationPrivate::app_font = new QFont(font);
     else
         *QGuiApplicationPrivate::app_font = font;
     applicationResourceFlags |= ApplicationFontExplicitlySet;
+
+    if (emitChange && qGuiApp)
+        emit qGuiApp->fontChanged(*QGuiApplicationPrivate::app_font);
 }
 
 /*!
diff --git a/src/gui/kernel/qguiapplication.h b/src/gui/kernel/qguiapplication.h
index 8560fcf18a..02dffef0fe 100644
--- a/src/gui/kernel/qguiapplication.h
+++ b/src/gui/kernel/qguiapplication.h
@@ -187,6 +187,7 @@ Q_SIGNALS:
 #endif
     void paletteChanged(const QPalette &pal);
     void applicationDisplayNameChanged();
+    void fontChanged(const QFont &font);
 
 protected:
     bool event(QEvent *) override;
diff --git a/tests/auto/gui/kernel/qguiapplication/tst_qguiapplication.cpp b/tests/auto/gui/kernel/qguiapplication/tst_qguiapplication.cpp
index 6ba488aaa7..4f27aeb899 100644
--- a/tests/auto/gui/kernel/qguiapplication/tst_qguiapplication.cpp
+++ b/tests/auto/gui/kernel/qguiapplication/tst_qguiapplication.cpp
@@ -68,6 +68,7 @@ private slots:
     void changeFocusWindow();
     void keyboardModifiers();
     void palette();
+    void font();
     void modalWindow();
     void quitOnLastWindowClosed();
     void quitOnLastWindowClosedMulti();
@@ -524,6 +525,31 @@ void tst_QGuiApplication::palette()
     QCOMPARE(signalSpy.count(), 2);
 }
 
+void tst_QGuiApplication::font()
+{
+    int argc = 1;
+    char *argv[] = { const_cast<char*>("tst_qguiapplication") };
+    QGuiApplication app(argc, argv);
+    QSignalSpy signalSpy(&app, SIGNAL(fontChanged(QFont)));
+
+    QFont oldFont = QGuiApplication::font();
+    QFont newFont = QFont("BogusFont", 33);
+
+    QGuiApplication::setFont(newFont);
+    QCOMPARE(QGuiApplication::font(), newFont);
+    QCOMPARE(signalSpy.count(), 1);
+    QCOMPARE(signalSpy.at(0).at(0), QVariant(newFont));
+
+    QGuiApplication::setFont(oldFont);
+    QCOMPARE(QGuiApplication::font(), oldFont);
+    QCOMPARE(signalSpy.count(), 2);
+    QCOMPARE(signalSpy.at(1).at(0), QVariant(oldFont));
+
+    QGuiApplication::setFont(oldFont);
+    QCOMPARE(QGuiApplication::font(), oldFont);
+    QCOMPARE(signalSpy.count(), 2);
+}
+
 class BlockableWindow : public QWindow
 {
     Q_OBJECT