QListView: Speedup handling of hidden items

Instead iterating through all rows to get the number of hidden items,
iterate over the hidden items which are fewer items.
Also don't create a temporary vector with visible flow positions by
remembering the count of hidden items before the working index and
adjusting them appropriately which gives a significant performance
boost when working with a large data set.

[ChangeLog][QtWidgets][QListWidget] Speedup handling of hidden items
when working with large data sets

Task-number: QTBUG-68977
Change-Id: I599b6e97945c245f02229145baad8363ec2bf2f5
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

1 files changed, 4 insertions, 0 deletions

diff --git a/tests/auto/widgets/itemviews/qlistview/tst_qlistview.cpp b/tests/auto/widgets/itemviews/qlistview/tst_qlistview.cpp
index 5227db64ec..433b9e55e1 100644
--- a/tests/auto/widgets/itemviews/qlistview/tst_qlistview.cpp
+++ b/tests/auto/widgets/itemviews/qlistview/tst_qlistview.cpp
@@ -873,6 +873,10 @@ void tst_QListView::setCurrentIndex()
             }
         }
     }
+    while (model.rowCount()) {
+        view.setCurrentIndex(model.index(model.rowCount() - 1, 0));
+        model.removeRow(model.rowCount() - 1);
+    }
 }
 
 class PublicListView : public QListView