Add QHeaderView::setFirstSectionMovable(), useful for flat treeviews

QTreeView makes columns movable except for the first one
(since Qt 5.0, see commit e0fc088c0c). This is indeed best
for actual trees, but not when using QTreeView as a flat
multi-column list (with no "root decoration"). Then it should
be possible to move the first column.

[ChangeLog][QtWidgets][QHeaderView] Flat treeviews can now allow
the user to move the first column (like in Qt 4.x) using the new
method QHeaderView::setFirstSectionMovable().

Change-Id: I6b5025e40850bf5c4c373124ee81f657f3f09d29
Reviewed-by: Thorbjørn Lund Martsum <tmartsum@gmail.com>

5 files changed, 48 insertions, 9 deletions

diff --git a/src/widgets/itemviews/qheaderview.cpp b/src/widgets/itemviews/qheaderview.cpp
index abd5997ea1..4c5d17ba69 100644
--- a/src/widgets/itemviews/qheaderview.cpp
+++ b/src/widgets/itemviews/qheaderview.cpp
@@ -1115,10 +1115,15 @@ int QHeaderView::logicalIndex(int visualIndex) const
 /*!
     \since 5.0
 
-    If \a movable is true, the header may be moved by the user; otherwise it
-    is fixed in place.
+    If \a movable is true, the header sections may be moved by the user;
+    otherwise they are fixed in place.
+
+    When used in combination with QTreeView, the first column is not
+    movable (since it contains the tree structure), by default.
+    You can make it movable with setFirstSectionMovable(true).
 
     \sa sectionsMovable(), sectionMoved()
+    \sa setFirstSectionMovable()
 */
 
 void QHeaderView::setSectionsMovable(bool movable)
@@ -1143,6 +1148,9 @@ void QHeaderView::setSectionsMovable(bool movable)
     Returns \c true if the header can be moved by the user; otherwise returns
     false.
 
+    By default, sections are movable in QTreeView (except for the first one),
+    and not movable in QTableView.
+
     \sa setSectionsMovable()
 */
 
@@ -1163,6 +1171,39 @@ bool QHeaderView::sectionsMovable() const
 */
 
 /*!
+    \since 5.10
+
+    If \a movable is true, the first column can be moved by the user.
+    In a QTreeView, the first column holds the tree structure and is
+    therefore non-movable by default, even after setSectionsMovable(true).
+
+    It can be made movable again, for instance in the case of flat lists
+    without a tree structure, by calling this method.
+    In such a scenario, it is recommended to call QTreeView::setRootIsDecorated(false)
+    as well.
+
+    This method has no effect unless setSectionsMovable(true) is called as well.
+    \sa setSectionsMovable()
+*/
+void QHeaderView::setFirstSectionMovable(bool movable)
+{
+    Q_D(QHeaderView);
+    d->allowUserMoveOfSection0 = movable;
+}
+
+/*!
+    \since 5.10
+
+    Returns \c true if the first column can be moved by the user,
+    when this header is used in a QTreeView.
+*/
+bool QHeaderView::firstSectionMovable() const
+{
+    Q_D(const QHeaderView);
+    return d->allowUserMoveOfSection0;
+}
+
+/*!
     \since 5.0
 
     If \a clickable is true, the header will respond to single clicks.
diff --git a/src/widgets/itemviews/qheaderview.h b/src/widgets/itemviews/qheaderview.h
index ec00d16d10..cfe2d24453 100644
--- a/src/widgets/itemviews/qheaderview.h
+++ b/src/widgets/itemviews/qheaderview.h
@@ -118,6 +118,8 @@ public:
     inline QT_DEPRECATED void setMovable(bool movable) { setSectionsMovable(movable); }
     inline QT_DEPRECATED bool isMovable() const { return sectionsMovable(); }
 #endif
+    void setFirstSectionMovable(bool movable);
+    bool firstSectionMovable() const;
 
     void setSectionsClickable(bool clickable);
     bool sectionsClickable() const;
diff --git a/src/widgets/itemviews/qheaderview_p.h b/src/widgets/itemviews/qheaderview_p.h
index 3b8e61af75..d844274618 100644
--- a/src/widgets/itemviews/qheaderview_p.h
+++ b/src/widgets/itemviews/qheaderview_p.h
@@ -246,10 +246,6 @@ public:
         }
     }
 
-    inline void setAllowUserMoveOfSection0(bool b) {
-        allowUserMoveOfSection0 = b;
-    }
-
     void clear();
     void flipSortIndicator(int section);
     void cascadingResize(int visual, int newSize);
diff --git a/src/widgets/itemviews/qtableview.cpp b/src/widgets/itemviews/qtableview.cpp
index fd3bdfd065..3b0a738d38 100644
--- a/src/widgets/itemviews/qtableview.cpp
+++ b/src/widgets/itemviews/qtableview.cpp
@@ -1226,7 +1226,7 @@ void QTableView::setHorizontalHeader(QHeaderView *header)
         delete d->horizontalHeader;
     d->horizontalHeader = header;
     d->horizontalHeader->setParent(this);
-    d->horizontalHeader->d_func()->setAllowUserMoveOfSection0(true);
+    d->horizontalHeader->setFirstSectionMovable(true);
     if (!d->horizontalHeader->model()) {
         d->horizontalHeader->setModel(d->model);
         if (d->selectionModel)
@@ -1264,7 +1264,7 @@ void QTableView::setVerticalHeader(QHeaderView *header)
         delete d->verticalHeader;
     d->verticalHeader = header;
     d->verticalHeader->setParent(this);
-    d->verticalHeader->d_func()->setAllowUserMoveOfSection0(true);
+    d->verticalHeader->setFirstSectionMovable(true);
     if (!d->verticalHeader->model()) {
         d->verticalHeader->setModel(d->model);
         if (d->selectionModel)
diff --git a/src/widgets/itemviews/qtreeview.cpp b/src/widgets/itemviews/qtreeview.cpp
index 6ea180dcf2..e1cb16db8a 100644
--- a/src/widgets/itemviews/qtreeview.cpp
+++ b/src/widgets/itemviews/qtreeview.cpp
@@ -311,7 +311,7 @@ void QTreeView::setHeader(QHeaderView *header)
         delete d->header;
     d->header = header;
     d->header->setParent(this);
-    d->header->d_func()->setAllowUserMoveOfSection0(false);
+    d->header->setFirstSectionMovable(false);
 
     if (!d->header->model()) {
         d->header->setModel(d->model);