QHeaderView - add parameter to control sizeHint precision

Currently Qt looks at 1000 rows when scaling a column.
That can be slow in some situations and too inaccurate in others.

With this patch we leave it up to the user to decide how precise
e.g resizeToContents should be.

Change-Id: I6ef60f9a3bb40fc331ce1a1544fdc77488d20ca3
Reviewed-by: Stephen Kelly <stephen.kelly@kdab.com>

1 files changed, 54 insertions, 1 deletions

diff --git a/src/widgets/itemviews/qheaderview.cpp b/src/widgets/itemviews/qheaderview.cpp
index d95e693126..c9a845fc7b 100644
--- a/src/widgets/itemviews/qheaderview.cpp
+++ b/src/widgets/itemviews/qheaderview.cpp
@@ -1253,7 +1253,7 @@ void QHeaderView::setSectionResizeMode(ResizeMode mode)
     property is set to true. This is the default for the horizontal headers provided
     by QTreeView.
 
-    \sa setStretchLastSection()
+    \sa setStretchLastSection(), resizeContentsPrecision()
 */
 
 void QHeaderView::setSectionResizeMode(int logicalIndex, ResizeMode mode)
@@ -1316,6 +1316,53 @@ QHeaderView::ResizeMode QHeaderView::sectionResizeMode(int logicalIndex) const
     return d->headerSectionResizeMode(visual);
 }
 
+/*!
+   \since 5.2
+   Sets how precise QHeaderView should calculate the size when ResizeToContents is used.
+   A low value will provide a less accurate but fast auto resize while a higher
+   value will provide a more accurate resize that however can be slow.
+
+   The number \a precision specifies how many sections that should be consider
+   when calculating the preferred size.
+
+   The default value is 1000 meaning that a horizontal column with auto-resize will look
+   at maximum 1000 rows on calculating when doing an auto resize.
+
+   Special value 0 means that it will look at only the visible area.
+   Special value -1 will imply looking at all elements.
+
+   This value is used in QTableView::sizeHintForColumn(), QTableView::sizeHintForRow()
+   and QTreeView::sizeHintForColumn(). Reimplementing these functions can make this
+   function not having an effect.
+
+   If \a resizeSectionsNow is set to true (default) it will do adjustment of sections by calling
+   resizeSections().  (regardless if the precision was changed).
+
+    \sa resizeContentsPrecision(), setSectionResizeMode(), resizeSections(), QTableView::sizeHintForColumn(), QTableView::sizeHintForRow(), QTreeView::sizeHintForColumn()
+*/
+
+void QHeaderView::setResizeContentsPrecision(int precision, bool resizeSectionsNow)
+{
+    Q_D(QHeaderView);
+    d->resizeContentsPrecision = precision;
+    if (resizeSectionsNow)
+        resizeSections();
+}
+
+/*!
+  \since 5.2
+  Returns how precise QHeaderView will calculate on ResizeToContents.
+
+  \sa setResizeContentsPrecision(), setSectionResizeMode()
+
+*/
+
+int QHeaderView::resizeContentsPrecision() const
+{
+    Q_D(const QHeaderView);
+    return d->resizeContentsPrecision;
+}
+
 // ### Qt 6 - remove this obsolete function
 /*!
     \obsolete
@@ -3583,6 +3630,8 @@ void QHeaderViewPrivate::write(QDataStream &out) const
     out << int(globalResizeMode);
 
     out << sectionItems;
+    if (out.version() >= QDataStream::Qt_5_2)
+        out << resizeContentsPrecision;
 }
 
 bool QHeaderViewPrivate::read(QDataStream &in)
@@ -3634,6 +3683,10 @@ bool QHeaderViewPrivate::read(QDataStream &in)
     }
     sectionItems = newSectionItems;
     recalcSectionStartPos();
+
+    if (in.version() >= QDataStream::Qt_5_2)
+        in >> resizeContentsPrecision;
+
     return true;
 }