QHeaderView: allow un-sorting of models

If one clicks on a QHeaderView's section, the header view will
sort the view by the respective column/row. By clicking multiple
times, one is able to toggle the sorting between ascending
and descending. Something that is NOT possible to do however is to
un-sort the view -- that is, to restore the model's original
sorting. This must be done via code, by asking the header or the
view to sort by section -1.

This commit adds new property to QHeaderView to make it possible
to unsort models. Basically, the sort indicator becomes a tri-state:
sort ascending, sort descending, unsort (sort by column -1).

[ChangeLog][QtWidgets][QHeaderView] Added the sortIndicatorClearable
property. Setting this property allows the user to clear the sort
indicator on a section, resetting the model to its default ordering.

Change-Id: Ibf4e280b2086b75ccd64d619ea4d70816dc3529f
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
Reviewed-by: David Faure <david.faure@kdab.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/src/widgets/itemviews/qheaderview.h b/src/widgets/itemviews/qheaderview.h
index a836f4a50a..baad5c024b 100644
--- a/src/widgets/itemviews/qheaderview.h
+++ b/src/widgets/itemviews/qheaderview.h
@@ -62,6 +62,7 @@ class Q_WIDGETS_EXPORT QHeaderView : public QAbstractItemView
     Q_PROPERTY(int minimumSectionSize READ minimumSectionSize WRITE setMinimumSectionSize)
     Q_PROPERTY(int maximumSectionSize READ maximumSectionSize WRITE setMaximumSectionSize)
     Q_PROPERTY(Qt::Alignment defaultAlignment READ defaultAlignment WRITE setDefaultAlignment)
+    Q_PROPERTY(bool sortIndicatorClearable READ isSortIndicatorClearable WRITE setSortIndicatorClearable NOTIFY sortIndicatorClearableChanged)
 
 public:
 
@@ -140,6 +141,9 @@ public:
     int sortIndicatorSection() const;
     Qt::SortOrder sortIndicatorOrder() const;
 
+    void setSortIndicatorClearable(bool clearable);
+    bool isSortIndicatorClearable() const;
+
     bool stretchLastSection() const;
     void setStretchLastSection(bool stretch);
 
@@ -186,6 +190,7 @@ Q_SIGNALS:
     void sectionHandleDoubleClicked(int logicalIndex);
     void geometriesChanged();
     void sortIndicatorChanged(int logicalIndex, Qt::SortOrder order);
+    void sortIndicatorClearableChanged(bool clearable);
 
 protected Q_SLOTS:
     void updateSection(int logicalIndex);