QAbstractItemView: trigger handlers (and redraw) when changing selection model

The most visible problem is that changing selection model didn't update()
the view, resulting in the old selection/current item still being drawn.
In general trigger the handlers for when the selection/current item
changes.

Change-Id: Ib3b2ad70412e6a21a182d4c173e617710bcc630d
Task-number: QTBUG-50535
Reviewed-by: Stephen Kelly <ske@ableton.com>

src/widgets/itemviews/qabstractitemview.cpp

@@ -765,7 +765,13 @@ void QAbstractItemView::setSelectionModel(QItemSelectionModel *selectionModel)
         return;
     }
 
+    QItemSelection oldSelection;
+    QModelIndex oldCurrentIndex;
+
     if (d->selectionModel) {
+        oldSelection = d->selectionModel->selection();
+        oldCurrentIndex = d->selectionModel->currentIndex();
+
         disconnect(d->selectionModel, SIGNAL(selectionChanged(QItemSelection,QItemSelection)),
                    this, SLOT(selectionChanged(QItemSelection,QItemSelection)));
         disconnect(d->selectionModel, SIGNAL(currentChanged(QModelIndex,QModelIndex)),
@@ -779,6 +785,9 @@ void QAbstractItemView::setSelectionModel(QItemSelectionModel *selectionModel)
                 this, SLOT(selectionChanged(QItemSelection,QItemSelection)));
         connect(d->selectionModel, SIGNAL(currentChanged(QModelIndex,QModelIndex)),
                 this, SLOT(currentChanged(QModelIndex,QModelIndex)));
+
+        selectionChanged(d->selectionModel->selection(), oldSelection);
+        currentChanged(d->selectionModel->currentIndex(), oldCurrentIndex);
     }
 }
 

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

@@ -37,6 +37,7 @@
 #include <qabstractitemview.h>
 #include <qstandarditemmodel.h>
 #include <qapplication.h>
+#include <qevent.h>
 #include <qlistview.h>
 #include <qlistwidget.h>
 #include <qtableview.h>
@@ -251,6 +252,7 @@ private slots:
     void sizeHintChangeTriggersLayout();
     void shiftSelectionAfterChangingModelContents();
     void QTBUG48968_reentrant_updateEditorGeometries();
+    void QTBUG50535_update_on_new_selection_model();
 };
 
 class MyAbstractItemDelegate : public QAbstractItemDelegate
@@ -2028,5 +2030,57 @@ void tst_QAbstractItemView::QTBUG48968_reentrant_updateEditorGeometries()
     // No crash, all fine.
 }
 
+void tst_QAbstractItemView::QTBUG50535_update_on_new_selection_model()
+{
+    QStandardItemModel model;
+    for (int i = 0; i < 10; ++i)
+        model.appendRow(new QStandardItem(QStringLiteral("%1").arg(i)));
+
+    class ListView : public QListView
+    {
+    public:
+        ListView()
+            : m_paintEventsCount(0)
+        {
+        }
+
+        int m_paintEventsCount;
+
+    protected:
+        bool viewportEvent(QEvent *event) Q_DECL_OVERRIDE
+        {
+            if (event->type() == QEvent::Paint)
+                ++m_paintEventsCount;
+            return QListView::viewportEvent(event);
+        }
+    };
+
+    // keep the current/selected row in the "low range", i.e. be sure it's visible, otherwise we
+    // don't get updates and the test fails.
+
+    ListView view;
+    view.setModel(&model);
+    view.selectionModel()->setCurrentIndex(model.index(1, 0), QItemSelectionModel::SelectCurrent);
+    view.show();
+    QVERIFY(QTest::qWaitForWindowExposed(&view));
+
+
+    QItemSelectionModel selectionModel(&model);
+    selectionModel.setCurrentIndex(model.index(2, 0), QItemSelectionModel::Current);
+
+    int oldPaintEventsCount = view.m_paintEventsCount;
+    view.setSelectionModel(&selectionModel);
+    QTRY_VERIFY(view.m_paintEventsCount > oldPaintEventsCount);
+
+
+    QItemSelectionModel selectionModel2(&model);
+    selectionModel2.select(model.index(0, 0), QItemSelectionModel::ClearAndSelect);
+    selectionModel2.setCurrentIndex(model.index(1, 0), QItemSelectionModel::Current);
+
+    oldPaintEventsCount = view.m_paintEventsCount;
+    view.setSelectionModel(&selectionModel2);
+    QTRY_VERIFY(view.m_paintEventsCount > oldPaintEventsCount);
+}
+
 QTEST_MAIN(tst_QAbstractItemView)
 #include "tst_qabstractitemview.moc"