Make the default value of QTreeView::indentation() be style dependent

Add a new PM_TreeViewIndentaion enum value to QStyle and get
the corresponding pixel metric in QTreeView.

[ChangeLog][QtWidgets][QTreeView] Indentation is now style-dependent by default.

[ChangeLog][QtWidgets][QTreeView] Added resetIndentation().

Change-Id: Ifad7987b8f3c6cd32987b89d95390f33043d8f19
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>
Reviewed-by: Adam Majer <adamm@zombino.com>

6 files changed, 41 insertions, 4 deletions

diff --git a/src/widgets/itemviews/qtreeview.cpp b/src/widgets/itemviews/qtreeview.cpp
index 3f952ff768..ae3994e30a 100644
--- a/src/widgets/itemviews/qtreeview.cpp
+++ b/src/widgets/itemviews/qtreeview.cpp
@@ -371,7 +371,9 @@ void QTreeView::setAutoExpandDelay(int delay)
   horizontal distance from the viewport edge to the items in the first column;
   for child items, it specifies their indentation from their parent items.
 
-  By default, this property has a value of 20.
+  By default, the value of this property is style dependent. Thus, when the style
+  changes, this property updates from it. Calling setIndentation() stops the updates,
+  calling resetIndentation() will restore default behavior.
 */
 int QTreeView::indentation() const
 {
@@ -382,12 +384,22 @@ int QTreeView::indentation() const
 void QTreeView::setIndentation(int i)
 {
     Q_D(QTreeView);
-    if (i != d->indent) {
+    if (!d->customIndent || (i != d->indent)) {
         d->indent = i;
+        d->customIndent = true;
         d->viewport->update();
     }
 }
 
+void QTreeView::resetIndentation()
+{
+    Q_D(QTreeView);
+    if (d->customIndent) {
+        d->updateIndentationFromStyle();
+        d->customIndent = false;
+    }
+}
+
 /*!
   \property QTreeView::rootIsDecorated
   \brief whether to show controls for expanding and collapsing top-level items
@@ -2081,6 +2093,12 @@ QModelIndex QTreeView::indexBelow(const QModelIndex &index) const
 void QTreeView::doItemsLayout()
 {
     Q_D(QTreeView);
+    if (!d->customIndent) {
+        // ### Qt 6: move to event()
+        // QAbstractItemView calls this method in case of a style change,
+        // so update the indentation here if it wasn't set manually.
+        d->updateIndentationFromStyle();
+    }
     if (d->hasRemovedItems) {
         //clean the QSet that may contains old (and this invalid) indexes
         d->hasRemovedItems = false;
@@ -3025,6 +3043,8 @@ bool QTreeView::isIndexHidden(const QModelIndex &index) const
 void QTreeViewPrivate::initialize()
 {
     Q_Q(QTreeView);
+
+    updateIndentationFromStyle();
     updateStyledFrameWidths();
     q->setSelectionBehavior(QAbstractItemView::SelectRows);
     q->setSelectionMode(QAbstractItemView::SingleSelection);
@@ -3911,6 +3931,12 @@ int QTreeViewPrivate::accessibleTree2Index(const QModelIndex &index) const
     return (q->visualIndex(index) + (q->header() ? 1 : 0)) * index.model()->columnCount() + index.column();
 }
 
+void QTreeViewPrivate::updateIndentationFromStyle()
+{
+    Q_Q(const QTreeView);
+    indent = q->style()->pixelMetric(QStyle::PM_TreeViewIndentation, 0, q);
+}
+
 /*!
   \reimp
  */
diff --git a/src/widgets/itemviews/qtreeview.h b/src/widgets/itemviews/qtreeview.h
index 429b9d3add..8ac53b8bb7 100644
--- a/src/widgets/itemviews/qtreeview.h
+++ b/src/widgets/itemviews/qtreeview.h
@@ -56,7 +56,7 @@ class Q_WIDGETS_EXPORT QTreeView : public QAbstractItemView
 {
     Q_OBJECT
     Q_PROPERTY(int autoExpandDelay READ autoExpandDelay WRITE setAutoExpandDelay)
-    Q_PROPERTY(int indentation READ indentation WRITE setIndentation)
+    Q_PROPERTY(int indentation READ indentation WRITE setIndentation RESET resetIndentation)
     Q_PROPERTY(bool rootIsDecorated READ rootIsDecorated WRITE setRootIsDecorated)
     Q_PROPERTY(bool uniformRowHeights READ uniformRowHeights WRITE setUniformRowHeights)
     Q_PROPERTY(bool itemsExpandable READ itemsExpandable WRITE setItemsExpandable)
@@ -83,6 +83,7 @@ public:
 
     int indentation() const;
     void setIndentation(int i);
+    void resetIndentation();
 
     bool rootIsDecorated() const;
     void setRootIsDecorated(bool show);
diff --git a/src/widgets/itemviews/qtreeview_p.h b/src/widgets/itemviews/qtreeview_p.h
index 5d6333e856..c44d6d7ced 100644
--- a/src/widgets/itemviews/qtreeview_p.h
+++ b/src/widgets/itemviews/qtreeview_p.h
@@ -89,7 +89,7 @@ public:
           uniformRowHeights(false), rootDecoration(true),
           itemsExpandable(true), sortingEnabled(false),
           expandsOnDoubleClick(true),
-          allColumnsShowFocus(false), current(0), spanning(false),
+          allColumnsShowFocus(false), customIndent(false), current(0), spanning(false),
           animationsEnabled(false), columnResizeTimerID(0),
           autoExpandDelay(-1), hoverBranch(-1), geometryRecursionBlock(false), hasRemovedItems(false),
           treePosition(0) {}
@@ -191,6 +191,7 @@ public:
     bool sortingEnabled;
     bool expandsOnDoubleClick;
     bool allColumnsShowFocus;
+    bool customIndent;
 
     // used for drawing
     mutable QPair<int,int> leftAndRight;
@@ -241,6 +242,8 @@ public:
 
     int accessibleTree2Index(const QModelIndex &index) const;
 
+    void updateIndentationFromStyle();
+
     // used for spanning rows
     QVector<QPersistentModelIndex> spanningIndexes;
 
diff --git a/src/widgets/styles/qcommonstyle.cpp b/src/widgets/styles/qcommonstyle.cpp
index ce6d3d708f..ec289e896b 100644
--- a/src/widgets/styles/qcommonstyle.cpp
+++ b/src/widgets/styles/qcommonstyle.cpp
@@ -4695,6 +4695,9 @@ int QCommonStyle::pixelMetric(PixelMetric m, const QStyleOption *opt, const QWid
     case PM_SubMenuOverlap:
         ret = -proxy()->pixelMetric(QStyle::PM_MenuPanelWidth, opt, widget);
         break;
+    case PM_TreeViewIndentation:
+        ret = int(QStyleHelper::dpiScaled(20.));
+        break;
     default:
         ret = 0;
         break;
diff --git a/src/widgets/styles/qstyle.cpp b/src/widgets/styles/qstyle.cpp
index fb5a5c9003..c3be177732 100644
--- a/src/widgets/styles/qstyle.cpp
+++ b/src/widgets/styles/qstyle.cpp
@@ -1470,6 +1470,9 @@ void QStyle::drawItemPixmap(QPainter *painter, const QRect &rect, int alignment,
     \value PM_TabCloseIndicatorWidth The default width of a close button on a tab in a tab bar.
     \value PM_TabCloseIndicatorHeight The default height of a close button on a tab in a tab bar.
 
+    \value PM_TreeViewIndentation The indentation of items in a tree view.
+           This enum value has been introduced in Qt 5.4.
+
     \value PM_CustomBase Base value for custom pixel metrics.  Custom
     values must be greater than this value.
 
diff --git a/src/widgets/styles/qstyle.h b/src/widgets/styles/qstyle.h
index a2de839404..c647513dca 100644
--- a/src/widgets/styles/qstyle.h
+++ b/src/widgets/styles/qstyle.h
@@ -556,6 +556,7 @@ public:
         PM_ScrollView_ScrollBarSpacing,
         PM_ScrollView_ScrollBarOverlap,
         PM_SubMenuOverlap,
+        PM_TreeViewIndentation,
 
         // do not add any values below/greater than this
         PM_CustomBase = 0xf0000000