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>

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
  */

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);

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;
 

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;

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.
 

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

tests/auto/widgets/itemviews/qtreeview/tst_qtreeview.cpp

@@ -212,6 +212,7 @@ private slots:
     void rowSizeHint();
     void setSortingEnabled();
     void headerHidden();
+    void indentation();
 
     void selection();
     void removeAndInsertExpandedCol0();
@@ -439,7 +440,8 @@ void tst_QTreeView::getSetCheck()
 
     // int QTreeView::indentation()
     // void QTreeView::setIndentation(int)
-    QCOMPARE(obj1.indentation(), 20);
+    const int styledIndentation = obj1.style()->pixelMetric(QStyle::PM_TreeViewIndentation, 0, &obj1);
+    QCOMPARE(obj1.indentation(), styledIndentation);
     obj1.setIndentation(0);
     QCOMPARE(obj1.indentation(), 0);
     obj1.setIndentation(INT_MIN);
@@ -554,7 +556,8 @@ void tst_QTreeView::construction()
     QCOMPARE(view.columnWidth(0), 0);
     QCOMPARE(view.columnWidth(1), 0);
     QVERIFY(view.header());
-    QCOMPARE(view.indentation(), 20);
+    const int styledIndentation = view.style()->pixelMetric(QStyle::PM_TreeViewIndentation, 0, &view);
+    QCOMPARE(view.indentation(), styledIndentation);
     QCOMPARE(view.indexAbove(QModelIndex()), QModelIndex());
     QCOMPARE(view.indexBelow(QModelIndex()), QModelIndex());
     QVERIFY(!view.isAnimated());
@@ -2576,6 +2579,42 @@ void tst_QTreeView::headerHidden()
     QCOMPARE(view.header()->isHidden(), true);
 }
 
+class TestTreeViewStyle : public QProxyStyle
+{
+public:
+    TestTreeViewStyle() : indentation(20) {}
+    int pixelMetric(PixelMetric metric, const QStyleOption *option = 0, const QWidget *widget = 0) const Q_DECL_OVERRIDE
+    {
+        if (metric == QStyle::PM_TreeViewIndentation)
+            return indentation;
+        else
+            return QProxyStyle::pixelMetric(metric, option, widget);
+    }
+    int indentation;
+};
+
+void tst_QTreeView::indentation()
+{
+    TestTreeViewStyle style1;
+    TestTreeViewStyle style2;
+    style1.indentation = 20;
+    style2.indentation = 30;
+
+    QTreeView view;
+    view.setStyle(&style1);
+    QCOMPARE(view.indentation(), style1.indentation);
+    view.setStyle(&style2);
+    QCOMPARE(view.indentation(), style2.indentation);
+    view.setIndentation(70);
+    QCOMPARE(view.indentation(), 70);
+    view.setStyle(&style1);
+    QCOMPARE(view.indentation(), 70);
+    view.resetIndentation();
+    QCOMPARE(view.indentation(), style1.indentation);
+    view.setStyle(&style2);
+    QCOMPARE(view.indentation(), style2.indentation);
+}
+
 // From Task 145199 (crash when column 0 having at least one expanded item is removed and then
 // inserted). The test passes simply if it doesn't crash, hence there are no calls
 // to QCOMPARE() or QVERIFY().