QAbstractItemView - allow deselect in single selection mode.

This patch allows single selection to be cleared with the normal
control modifier. This affects e.g QTreeView and QListView.

Task-number: QTBUG-8836
Change-Id: I7fd50b987acc3552b36657409568192763257536
Reviewed-by: Stephen Kelly <stephen.kelly@kdab.com>

dist/changes-5.1.0

@@ -34,7 +34,10 @@ Third party components
 *                   Important Behavior Changes                             *
 ****************************************************************************
 
+- QtWidgets
 
+  * [QTBUG-8836] QAbstractItemView now allows manual deselect in
+    SingleSelection mode (with control modifier)
 
 ****************************************************************************
 *                          Library                                         *

src/widgets/itemviews/qabstractitemview.cpp

@@ -3816,13 +3816,31 @@ QItemSelectionModel::SelectionFlags QAbstractItemView::selectionCommand(const QM
                                                                         const QEvent *event) const
 {
     Q_D(const QAbstractItemView);
+    Qt::KeyboardModifiers keyModifiers = Qt::NoModifier;
+    if (event) {
+        switch (event->type()) {
+            case QEvent::MouseButtonDblClick:
+            case QEvent::MouseButtonPress:
+            case QEvent::MouseButtonRelease:
+            case QEvent::MouseMove:
+            case QEvent::KeyPress:
+            case QEvent::KeyRelease:
+                keyModifiers = (static_cast<const QInputEvent*>(event))->modifiers();
+                break;
+            default:
+                keyModifiers = QApplication::keyboardModifiers();
+        }
+    }
     switch (d->selectionMode) {
         case NoSelection: // Never update selection model
             return QItemSelectionModel::NoUpdate;
         case SingleSelection: // ClearAndSelect on valid index otherwise NoUpdate
             if (event && event->type() == QEvent::MouseButtonRelease)
                 return QItemSelectionModel::NoUpdate;
-            return QItemSelectionModel::ClearAndSelect|d->selectionBehaviorFlags();
+            if ((keyModifiers & Qt::ControlModifier) && d->selectionModel->isSelected(index))
+                return QItemSelectionModel::Deselect | d->selectionBehaviorFlags();
+            else
+                return QItemSelectionModel::ClearAndSelect | d->selectionBehaviorFlags();
         case MultiSelection:
             return d->multiSelectionCommand(index, event);
         case ExtendedSelection:

tests/auto/widgets/itemviews/qabstractitemview/tst_qabstractitemview.cpp

@@ -227,6 +227,7 @@ private slots:
     void testDelegateDestroyEditor();
     void testClickedSignal();
     void testChangeEditorState();
+    void deselectInSingleSelection();
 };
 
 class MyAbstractItemDelegate : public QAbstractItemDelegate
@@ -1591,5 +1592,47 @@ void tst_QAbstractItemView::testChangeEditorState()
     // No segfault - the test passes.
 }
 
+void tst_QAbstractItemView::deselectInSingleSelection()
+{
+    QTableView view;
+    QStandardItemModel s;
+    s.setRowCount(10);
+    s.setColumnCount(10);
+    view.setModel(&s);
+    view.show();
+    view.setSelectionMode(QAbstractItemView::SingleSelection);
+    view.setEditTriggers(QAbstractItemView::NoEditTriggers);
+    QApplication::setActiveWindow(&view);
+    QVERIFY(QTest::qWaitForWindowExposed(&view));
+    // mouse
+    QModelIndex index22 = s.index(2, 2);
+    QRect rect22 = view.visualRect(index22);
+    QPoint clickpos = rect22.center();
+    QTest::mouseClick(view.viewport(), Qt::LeftButton, Qt::NoModifier, clickpos);
+    QCOMPARE(view.currentIndex(), index22);
+    QCOMPARE(view.selectionModel()->selectedIndexes().count(), 1);
+    QTest::mouseClick(view.viewport(), Qt::LeftButton, Qt::ControlModifier, clickpos);
+    QCOMPARE(view.currentIndex(), index22);
+    QCOMPARE(view.selectionModel()->selectedIndexes().count(), 0);
+
+    // second click with modifier however does select
+    QTest::mouseClick(view.viewport(), Qt::LeftButton, Qt::ControlModifier, clickpos);
+    QCOMPARE(view.currentIndex(), index22);
+    QCOMPARE(view.selectionModel()->selectedIndexes().count(), 1);
+
+    // keyboard
+    QTest::keyClick(&view, Qt::Key_Space, Qt::NoModifier);
+    QCOMPARE(view.currentIndex(), index22);
+    QCOMPARE(view.selectionModel()->selectedIndexes().count(), 1);
+    QTest::keyClick(&view, Qt::Key_Space, Qt::ControlModifier);
+    QCOMPARE(view.currentIndex(), index22);
+    QCOMPARE(view.selectionModel()->selectedIndexes().count(), 0);
+
+    // second keypress with modifier however does select
+    QTest::keyClick(&view, Qt::Key_Space, Qt::ControlModifier);
+    QCOMPARE(view.currentIndex(), index22);
+    QCOMPARE(view.selectionModel()->selectedIndexes().count(), 1);
+}
+
 QTEST_MAIN(tst_QAbstractItemView)
 #include "tst_qabstractitemview.moc"

tests/manual/widgets/itemviews/qheaderview/qheaderviewtest1.cpp

@@ -99,6 +99,9 @@ int main(int argc, char *argv[])
     m.setRowCount(500);
     m.setColumnCount(250);
     tv.setModel(&m);
+    tv.setSelectionMode(QAbstractItemView::SingleSelection);
+    // Comment in the line below to test selection with keyboard (space)
+    // tv.setEditTriggers(QAbstractItemView::NoEditTriggers);
     SomeHandler handler(tv.horizontalHeader(), &tv);
     tv.horizontalHeader()->setDefaultSectionSize(30);
     tv.show();