QComboBox: Disable wheel events on OS X & iOS

This is follow-up for QTabBar fix ea47d152b3.

In native OS X applications using mouse wheel on combo boxes have absolutely no
effect. We should bring the same behavior to Qt based OS X apps too, as users
are complaining of unexpected behavior, eg. randomly switching Qt Creator
sidebar mode when scrolling file list and moving mouse pointer little bit
above. Moreover inertial mouse behavior on OS X makes combo box usually move
several indexes, rather than single one on slight finger slide.

This also applies to iOS apps so the change affects all Apple platforms.

Task-number: QTBUG-10707
Change-Id: I6582265039198707ad8c2f54de96ee2a0b0e0b47
Reviewed-by: Adam Strzelecki <ono@java.pl>
Reviewed-by: Jake Petroules <jake.petroules@theqtcompany.com>

src/widgets/widgets/qcombobox.cpp

@@ -3238,6 +3238,9 @@ void QComboBox::keyReleaseEvent(QKeyEvent *e)
 #ifndef QT_NO_WHEELEVENT
 void QComboBox::wheelEvent(QWheelEvent *e)
 {
+#ifdef Q_OS_DARWIN
+    Q_UNUSED(e);
+#else
     Q_D(QComboBox);
     if (!d->viewContainer()->isVisible()) {
         int newIndex = currentIndex();
@@ -3258,6 +3261,7 @@ void QComboBox::wheelEvent(QWheelEvent *e)
         }
         e->accept();
     }
+#endif
 }
 #endif
 

tests/auto/widgets/widgets/qcombobox/tst_qcombobox.cpp

@@ -2044,7 +2044,13 @@ void tst_QComboBox::mouseWheel_data()
     QTest::newRow("upper locked") << disabled << start << wheel << expected;
 
     wheel = -1;
+#ifdef Q_OS_DARWIN
+    // on OS X & iOS mouse wheel shall have no effect on combo box
+    expected = start;
+#else
+    // on other OSes we should jump to next enabled item (no. 5)
     expected = 5;
+#endif
     QTest::newRow("jump over") << disabled << start << wheel << expected;
 
     disabled.clear();