QTreeView - allow users to control data in the treestructure

This patch allows to set which logical index the tree is in.

Before the tree always displayed data from the logical index 0,
but it is actually more likely that the user wants to have data
from visual index 0 (which can be done by special value -1).

There is nothing special about logical index 0, and not being
able to change the tree-data is just annoying.

Change-Id: Ib070ce93343a0d2fbac3ad5a42cb4359401ac87c
Reviewed-by: Stephen Kelly <stephen.kelly@kdab.com>

3 files changed, 58 insertions, 8 deletions

diff --git a/src/widgets/itemviews/qtreeview.cpp b/src/widgets/itemviews/qtreeview.cpp
index bbbfb817f0..b1ac4eba7b 100644
--- a/src/widgets/itemviews/qtreeview.cpp
+++ b/src/widgets/itemviews/qtreeview.cpp
@@ -953,6 +953,36 @@ bool QTreeView::wordWrap() const
     return d->wrapItemText;
 }
 
+/*!
+    \since 5.2
+
+    This specifies that the tree structure should be placed at logical index \a index.
+    If \index is set to -1 then the tree will always follow visual index 0.
+
+    \sa treePosition(), QHeaderView::swapSections(), QHeaderView::moveSection()
+*/
+
+void QTreeView::setTreePosition(int index)
+{
+    Q_D(QTreeView);
+    d->treePosition = index;
+    update();
+}
+
+/*!
+    \since 5.2
+
+    Return the logical index the tree is set on. If the return value is -1 then the
+    tree is placed on the visual index 0.
+
+    \sa setTreePosition()
+*/
+
+int QTreeView::treePosition() const
+{
+    Q_D(const QTreeView);
+    return d->treePosition;
+}
 
 /*!
   \reimp
@@ -1068,7 +1098,7 @@ QRect QTreeView::visualRect(const QModelIndex &index) const
     int x = (spanning ? 0 : columnViewportPosition(index.column()));
     int w = (spanning ? d->header->length() : columnWidth(index.column()));
     // handle indentation
-    if (index.column() == 0) {
+    if (d->isTreePosition(index.column())) {
         int i = d->indentationForItem(vi);
         w -= i;
         if (!isRightToLeft())
@@ -1285,6 +1315,14 @@ void QTreeView::paintEvent(QPaintEvent *event)
     }
 }
 
+int QTreeViewPrivate::logicalIndexForTree() const
+{
+    int index = treePosition;
+    if (index < 0)
+        index = header->logicalIndex(0);
+    return index;
+}
+
 void QTreeViewPrivate::paintAlternatingRowColors(QPainter *painter, QStyleOptionViewItem *option, int y, int bottom) const
 {
     Q_Q(const QTreeView);
@@ -1517,7 +1555,7 @@ void QTreeViewPrivate::calcLogicalIndices(QVector<int> *logicalIndices, QVector<
         if (columnCount == 1 || (nextLogicalSection == 0 && prevLogicalSection == -1)
             || (headerSection == 0 && nextLogicalSection == -1) || spanning)
             pos = QStyleOptionViewItem::OnlyOne;
-        else if (headerSection == 0 || (nextLogicalSection != 0 && prevLogicalSection == -1))
+        else if (isTreePosition(headerSection) || (nextLogicalSection != 0 && prevLogicalSection == -1))
             pos = QStyleOptionViewItem::Beginning;
         else if (nextLogicalSection == 0 || nextLogicalSection == -1)
             pos = QStyleOptionViewItem::End;
@@ -1541,7 +1579,7 @@ int QTreeViewPrivate::widthHintForIndex(const QModelIndex &index, int hint, cons
         hint = qBound(min, hint, max);
     }
     int xhint = delegateForIndex(index)->sizeHint(option, index).width();
-    hint = qMax(hint, xhint + (index.column() == 0 ? indentationForItem(i) : 0));
+    hint = qMax(hint, xhint + (isTreePosition(index.column()) ? indentationForItem(i) : 0));
     return hint;
 }
 
@@ -1686,7 +1724,7 @@ void QTreeView::drawRow(QPainter *painter, const QStyleOptionViewItem &option,
            alternate row color was provided by the view. For backward compatibility,
            this is now delegated to the style using PE_PanelViewItemRow which
            does the appropriate fill */
-        if (headerSection == 0) {
+        if (d->isTreePosition(headerSection)) {
             const int i = d->indentationForItem(d->current);
             QRect branches(reverse ? position + width - i : position, y, i, height);
             const bool setClipRect = branches.width() > width;
@@ -3663,7 +3701,7 @@ int QTreeViewPrivate::itemDecorationAt(const QPoint &pos) const
     executePostedLayout();
     int x = pos.x();
     int column = header->logicalIndexAt(x);
-    if (column != 0)
+    if (!isTreePosition(column))
         return -1; // no logical index at x
 
     int viewItemIndex = itemAtCoordinate(pos.y());
@@ -3685,8 +3723,8 @@ QRect QTreeViewPrivate::itemDecorationRect(const QModelIndex &index) const
         return QRect();
 
     int itemIndentation = indentationForItem(viewItemIndex);
-    int position = header->sectionViewportPosition(0);
-    int size = header->sectionSize(0);
+    int position = header->sectionViewportPosition(logicalIndexForTree());
+    int size = header->sectionSize(logicalIndexForTree());
 
     QRect rect;
     if (q->isRightToLeft())
diff --git a/src/widgets/itemviews/qtreeview.h b/src/widgets/itemviews/qtreeview.h
index fae814c6f6..d9c6cd9269 100644
--- a/src/widgets/itemviews/qtreeview.h
+++ b/src/widgets/itemviews/qtreeview.h
@@ -128,6 +128,9 @@ public:
     void setWordWrap(bool on);
     bool wordWrap() const;
 
+    void setTreePosition(int logicalIndex);
+    int treePosition() const;
+
     void keyboardSearch(const QString &search);
 
     QRect visualRect(const QModelIndex &index) const;
diff --git a/src/widgets/itemviews/qtreeview_p.h b/src/widgets/itemviews/qtreeview_p.h
index 8be9c568d3..89de435606 100644
--- a/src/widgets/itemviews/qtreeview_p.h
+++ b/src/widgets/itemviews/qtreeview_p.h
@@ -91,10 +91,16 @@ public:
           expandsOnDoubleClick(true),
           allColumnsShowFocus(false), current(0), spanning(false),
           animationsEnabled(false), columnResizeTimerID(0),
-          autoExpandDelay(-1), hoverBranch(-1), geometryRecursionBlock(false), hasRemovedItems(false) {}
+          autoExpandDelay(-1), hoverBranch(-1), geometryRecursionBlock(false), hasRemovedItems(false),
+          treePosition(0) {}
 
     ~QTreeViewPrivate() {}
     void initialize();
+    int logicalIndexForTree() const;
+    inline bool isTreePosition(int logicalIndex) const
+    {
+        return logicalIndex == logicalIndexForTree();
+    }
 
     QItemViewPaintPairs draggablePaintPairs(const QModelIndexList &indexes, QRect *r) const;
     void adjustViewOptionsForIndex(QStyleOptionViewItem *option, const QModelIndex &current) const;
@@ -252,6 +258,9 @@ public:
 
     // If we should clean the set
     bool hasRemovedItems;
+
+    // tree position
+    int treePosition;
 };
 
 QT_END_NAMESPACE