Add itemAlignment property to QListView

This property allows to change the default behavior in
which list items occupy the entire width of their column.
Setting it to Qt::{AlignLeft,AlignRight,AlignHCenter} will
reduce their widths to the minimum values, thus allowing to
have intermediate free space. Then the user will be able to
begin selections by mouse from this space.

[ChangeLog][QtWidgets][QListView] Added itemAlignment property.

Task-number: QTBUG-56606
Change-Id: Iae55c251379be4e45d0c0d69175ff4388b5785b4
Reviewed-by: Christian Ehrlicher <ch.ehrlicher@gmx.de>
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

src/widgets/itemviews/qlistview.cpp

@@ -1630,6 +1630,32 @@ bool QListView::isSelectionRectVisible() const
     return d->isSelectionRectVisible();
 }
 
+/*!
+    \property QListView::itemAlignment
+    \brief the alignment of each item in its cell
+    \since 5.12
+
+    This is only supported in ListMode with TopToBottom flow
+    and with wrapping enabled.
+    The default alignment is 0, which means that an item fills
+    its cell entirely.
+*/
+void QListView::setItemAlignment(Qt::Alignment alignment)
+{
+    Q_D(QListView);
+    if (d->itemAlignment == alignment)
+        return;
+    d->itemAlignment = alignment;
+    if (viewMode() == ListMode && flow() == QListView::TopToBottom && isWrapping())
+        d->doDelayedItemsLayout();
+}
+
+Qt::Alignment QListView::itemAlignment() const
+{
+    Q_D(const QListView);
+    return d->itemAlignment;
+}
+
 /*!
     \reimp
 */
@@ -1656,7 +1682,8 @@ QListViewPrivate::QListViewPrivate()
       column(0),
       uniformItemSizes(false),
       batchSize(100),
-      showElasticBand(false)
+      showElasticBand(false),
+      itemAlignment(Qt::Alignment())
 {
 }
 
@@ -2366,6 +2393,7 @@ QListViewItem QListModeViewBase::indexToListViewItem(const QModelIndex &index) c
     options.rect.setSize(contentsSize);
     QSize size = (uniformItemSizes() && cachedItemSize().isValid())
                  ? cachedItemSize() : itemSize(options, index);
+    QSize cellSize = size;
 
     QPoint pos;
     if (flow() == QListView::LeftToRight) {
@@ -2378,12 +2406,22 @@ QListViewItem QListModeViewBase::indexToListViewItem(const QModelIndex &index) c
             int right = (segment + 1 >= segmentPositions.count()
                      ? contentsSize.width()
                      : segmentPositions.at(segment + 1));
-            size.setWidth(right - pos.x());
+            cellSize.setWidth(right - pos.x());
         } else { // make the items as wide as the viewport
-            size.setWidth(qMax(size.width(), viewport()->width() - 2 * spacing()));
+            cellSize.setWidth(qMax(size.width(), viewport()->width() - 2 * spacing()));
         }
     }
 
+    if (dd->itemAlignment & Qt::AlignHorizontal_Mask) {
+        size.setWidth(qMin(size.width(), cellSize.width()));
+        if (dd->itemAlignment & Qt::AlignRight)
+            pos.setX(pos.x() + cellSize.width() - size.width());
+        if (dd->itemAlignment & Qt::AlignHCenter)
+            pos.setX(pos.x() + (cellSize.width() - size.width()) / 2);
+    } else {
+        size.setWidth(cellSize.width());
+    }
+
     return QListViewItem(QRect(pos, size), index.row());
 }
 
@@ -2562,8 +2600,18 @@ QVector<QModelIndex> QListModeViewBase::intersectingSet(const QRect &area) const
             if (isHidden(row))
                 continue;
             QModelIndex index = modelIndex(row);
-            if (index.isValid())
-                ret += index;
+            if (index.isValid()) {
+                if (flow() == QListView::LeftToRight || dd->itemAlignment == Qt::Alignment()) {
+                    ret += index;
+                } else {
+                    const auto viewItem = indexToListViewItem(index);
+                    const int iw = viewItem.width();
+                    const int startPos = qMax(segStartPosition, segmentPositions.at(seg));
+                    const int endPos = qMin(segmentPositions.at(seg + 1), segEndPosition);
+                    if (endPos >= viewItem.x && startPos < viewItem.x + iw)
+                        ret += index;
+                }
+            }
 #if 0 // for debugging
             else
                 qWarning("intersectingSet: row %d was invalid", row);

src/widgets/itemviews/qlistview.h

@@ -65,6 +65,7 @@ class Q_WIDGETS_EXPORT QListView : public QAbstractItemView
     Q_PROPERTY(int batchSize READ batchSize WRITE setBatchSize)
     Q_PROPERTY(bool wordWrap READ wordWrap WRITE setWordWrap)
     Q_PROPERTY(bool selectionRectVisible READ isSelectionRectVisible WRITE setSelectionRectVisible)
+    Q_PROPERTY(Qt::Alignment itemAlignment READ itemAlignment WRITE setItemAlignment)
 
 public:
     enum Movement { Static, Free, Snap };
@@ -125,6 +126,9 @@ public:
     void setSelectionRectVisible(bool show);
     bool isSelectionRectVisible() const;
 
+    void setItemAlignment(Qt::Alignment alignment);
+    Qt::Alignment itemAlignment() const;
+
     QRect visualRect(const QModelIndex &index) const override;
     void scrollTo(const QModelIndex &index, ScrollHint hint = EnsureVisible) override;
     QModelIndex indexAt(const QPoint &p) const override;

src/widgets/itemviews/qlistview_p.h

@@ -431,6 +431,8 @@ public:
 
     QRect elasticBand;
     bool showElasticBand;
+
+    Qt::Alignment itemAlignment;
 };
 
 // inline implementations

tests/auto/widgets/itemviews/qlistview/tst_qlistview.cpp

@@ -149,6 +149,7 @@ private slots:
     void taskQTBUG_7232_AllowUserToControlSingleStep();
     void taskQTBUG_51086_skippingIndexesInSelectedIndexes();
     void taskQTBUG_47694_indexOutOfBoundBatchLayout();
+    void itemAlignment();
 };
 
 // Testing get/set functions
@@ -2544,5 +2545,28 @@ void tst_QListView::taskQTBUG_47694_indexOutOfBoundBatchLayout()
     view.scrollTo(model.index(batchSize - 1, 0));
 }
 
+void tst_QListView::itemAlignment()
+{
+    auto item1 = new QStandardItem("111");
+    auto item2 = new QStandardItem("111111");
+    QStandardItemModel model;
+    model.appendRow(item1);
+    model.appendRow(item2);
+
+    QListView w;
+    w.setModel(&model);
+    w.setWrapping(true);
+    w.show();
+    QVERIFY(QTest::qWaitForWindowExposed(&w));
+
+    QVERIFY(w.visualRect(item1->index()).width() > 0);
+    QVERIFY(w.visualRect(item1->index()).width() == w.visualRect(item2->index()).width());
+
+    w.setItemAlignment(Qt::AlignLeft);
+    QApplication::processEvents();
+
+    QVERIFY(w.visualRect(item1->index()).width() < w.visualRect(item2->index()).width());
+}
+
 QTEST_MAIN(tst_QListView)
 #include "tst_qlistview.moc"