Add SH_ItemView_ScrollMode style hint and use it in QMacStyle

On OS X, the default scrolling mode of item views should be
per pixel instead of per item. We enforce this through a new
style hint. On all other platforms, the behavior remains the
same.

It's still possible to override the style hint by using the
regular scroll mode setters. Any subsequent style change will
result in a no-op once the setters have been called and until
the properties are reset.

Some auto-tests had to be update to to take the new behavior
into account.

[ChangeLog][QtWidgets][Styles] Added SH_ItemView_ScrollMode
style hint.

[ChangeLog][QtWidgets][Item Views] Item views scroll per pixel
on OS X now.

[ChangeLog][QtWidgets][Item Views] QAbstractItemView::verticalScrollMode
and QAbstractItemView::horizontalScrollMode are now resettable.

Change-Id: I3f923275c99aa4389323b52fc1c5455fe71f8d73
Task-number: QTBUG-50102
Reviewed-by: Jake Petroules <jake.petroules@theqtcompany.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/src/widgets/itemviews/qabstractitemview.h b/src/widgets/itemviews/qabstractitemview.h
index fb1d222676..b8d386f234 100644
--- a/src/widgets/itemviews/qabstractitemview.h
+++ b/src/widgets/itemviews/qabstractitemview.h
@@ -75,8 +75,8 @@ class Q_WIDGETS_EXPORT QAbstractItemView : public QAbstractScrollArea
     Q_PROPERTY(SelectionBehavior selectionBehavior READ selectionBehavior WRITE setSelectionBehavior)
     Q_PROPERTY(QSize iconSize READ iconSize WRITE setIconSize NOTIFY iconSizeChanged)
     Q_PROPERTY(Qt::TextElideMode textElideMode READ textElideMode WRITE setTextElideMode)
-    Q_PROPERTY(ScrollMode verticalScrollMode READ verticalScrollMode WRITE setVerticalScrollMode)
-    Q_PROPERTY(ScrollMode horizontalScrollMode READ horizontalScrollMode WRITE setHorizontalScrollMode)
+    Q_PROPERTY(ScrollMode verticalScrollMode READ verticalScrollMode WRITE setVerticalScrollMode RESET resetVerticalScrollMode)
+    Q_PROPERTY(ScrollMode horizontalScrollMode READ horizontalScrollMode WRITE setHorizontalScrollMode RESET resetHorizontalScrollMode)
 
 public:
     enum SelectionMode {
@@ -147,9 +147,11 @@ public:
 
     void setVerticalScrollMode(ScrollMode mode);
     ScrollMode verticalScrollMode() const;
+    void resetVerticalScrollMode();
 
     void setHorizontalScrollMode(ScrollMode mode);
     ScrollMode horizontalScrollMode() const;
+    void resetHorizontalScrollMode();
 
     void setAutoScroll(bool enable);
     bool hasAutoScroll() const;