QListView: fixes skipping one item in pageDown(Up)

The previous implementation was scrolling down (number of visible items
in viewport) + 1 and this was leading to one item being skipped while doing
page down (the same also happened for page up). Now we are scrolling (number
of visible items in viewport) - 1 for each page down(up) (the '-1' is for
keeping the context, so the last item will turn into the first in case of
a page down, for example).

Task-number: QTBUG-5877
Reviewed-by: thierry

2 files changed, 38 insertions, 2 deletions

diff --git a/src/gui/itemviews/qlistview.cpp b/src/gui/itemviews/qlistview.cpp
index 31e5797..052308c 100644
--- a/src/gui/itemviews/qlistview.cpp
+++ b/src/gui/itemviews/qlistview.cpp
@@ -1147,7 +1147,9 @@ QModelIndex QListView::moveCursor(CursorAction cursorAction, Qt::KeyboardModifie
         }
         return d->closestIndex(initialRect, intersectVector);
     case MovePageUp:
-        rect.moveTop(rect.top() - d->viewport->height());
+        // move current by (visibileRowCount - 1) items.
+        // rect.translate(0, -rect.height()); will happen in the switch fallthrough for MoveUp.
+        rect.moveTop(rect.top() - d->viewport->height() + 2 * rect.height());
         if (rect.top() < rect.height())
             rect.moveTop(rect.height());
     case MovePrevious:
@@ -1173,7 +1175,9 @@ QModelIndex QListView::moveCursor(CursorAction cursorAction, Qt::KeyboardModifie
         }
         return d->closestIndex(initialRect, intersectVector);
     case MovePageDown:
-        rect.moveTop(rect.top() + d->viewport->height());
+        // move current by (visibileRowCount - 1) items.
+        // rect.translate(0, rect.height()); will happen in the switch fallthrough for MoveDown.
+        rect.moveTop(rect.top() + d->viewport->height() - 2 * rect.height());
         if (rect.bottom() > contents.height() - rect.height())
             rect.moveBottom(contents.height() - rect.height());
     case MoveNext:
diff --git a/tests/auto/qlistview/tst_qlistview.cpp b/tests/auto/qlistview/tst_qlistview.cpp
index bfd038e..596ac9b 100644
--- a/tests/auto/qlistview/tst_qlistview.cpp
+++ b/tests/auto/qlistview/tst_qlistview.cpp
@@ -122,6 +122,7 @@ private slots:
     void taskQTBUG_633_changeModelData();
     void taskQTBUG_435_deselectOnViewportClick();
     void taskQTBUG_2678_spacingAndWrappedText();
+    void taskQTBUG_5877_skippingItemInPageDownUp();
 };
 
 // Testing get/set functions
@@ -1881,5 +1882,36 @@ void tst_QListView::taskQTBUG_2678_spacingAndWrappedText()
     QCOMPARE(w.horizontalScrollBar()->minimum(), w.horizontalScrollBar()->maximum());
 }
 
+void tst_QListView::taskQTBUG_5877_skippingItemInPageDownUp()
+{
+    QList<int> currentItemIndexes;
+    QtTestModel model(0);
+    model.colCount = 1;
+    model.rCount = 100;
+
+    currentItemIndexes << 0 << 6 << 16 << 25 << 34 << 42 << 57 << 68 << 77
+                       << 83 << 91 << 94;
+    QMoveCursorListView vu;
+    vu.setModel(&model);
+    vu.show();
+
+    int itemHeight = vu.visualRect(model.index(0, 0)).height();
+    int visibleRowCount = vu.height() / itemHeight;
+    int scrolledRowCount = visibleRowCount - 1;
+
+    for (int i = 0; i < currentItemIndexes.size(); ++i) {
+        vu.selectionModel()->setCurrentIndex(model.index(currentItemIndexes[i], 0),
+                                             QItemSelectionModel::SelectCurrent);
+
+        QModelIndex idx = vu.moveCursor(QMoveCursorListView::MovePageDown, Qt::NoModifier);
+        int newCurrent = qMin(currentItemIndexes[i] + scrolledRowCount, 99);
+        QCOMPARE(idx, model.index(newCurrent, 0));
+
+        idx = vu.moveCursor(QMoveCursorListView::MovePageUp, Qt::NoModifier);
+        newCurrent = qMax(currentItemIndexes[i] - scrolledRowCount, 0);
+        QCOMPARE(idx, model.index(newCurrent, 0));
+    }
+}
+
 QTEST_MAIN(tst_QListView)
 #include "tst_qlistview.moc"