QQuickListView: ensure we re-layout when a delegate is placed at the last visible pos

The current implementation would only return true if the added
delegate was positioned below the last visible pixel. This caused
a problem when the position ended up at exactly the last visible
position, since then we would return false, meaning that a re-layout
would not be done.

Since we use the same calculations several places, this patch
will factor it out into lastVisiblePos, and also fix up the
places where we test on it. Especially this includes making
sure that we set visibleAffected to true if we actually
enter the for-loop that adds the item to visibleItems. To
make the code more readable (and to ensure that we are
consistent), we set it to true inside the for-loop.

Task-number: QTBUG-61537
Change-Id: Ie697b5b6d9f4236ee856bde75fd9bc0a07dda7ea
Reviewed-by: J-P Nurmi <jpnurmi@qt.io>

1 files changed, 4 insertions, 6 deletions

diff --git a/src/quick/items/qquicklistview.cpp b/src/quick/items/qquicklistview.cpp
index edfa970035..a6236d9801 100644
--- a/src/quick/items/qquicklistview.cpp
+++ b/src/quick/items/qquicklistview.cpp
@@ -3208,6 +3208,7 @@ bool QQuickListViewPrivate::applyInsertionChange(const QQmlChangeSet::Change &ch
 
     qreal tempPos = isContentFlowReversed() ? -position()-size() : position();
     int index = visibleItems.count() ? mapFromModel(modelIndex) : 0;
+    qreal lastVisiblePos = buffer + displayMarginEnd + tempPos + size();
 
     if (index < 0) {
         int i = visibleItems.count() - 1;
@@ -3217,7 +3218,7 @@ bool QQuickListViewPrivate::applyInsertionChange(const QQmlChangeSet::Change &ch
             // there are no visible items except items marked for removal
             index = visibleItems.count();
         } else if (visibleItems.at(i)->index + 1 == modelIndex
-            && visibleItems.at(i)->endPosition() <= buffer+displayMarginEnd+tempPos+size()) {
+            && visibleItems.at(i)->endPosition() <= lastVisiblePos) {
             // Special case of appending an item to the model.
             index = visibleItems.count();
         } else {
@@ -3305,11 +3306,8 @@ bool QQuickListViewPrivate::applyInsertionChange(const QQmlChangeSet::Change &ch
         }
 
     } else {
-        qreal to = buffer + displayMarginEnd + tempPos + size();
-
-        visibleAffected = count > 0 && pos < to;
-
-        for (int i = 0; i < count && pos <= to; ++i) {
+        for (int i = 0; i < count && pos <= lastVisiblePos; ++i) {
+            visibleAffected = true;
             FxViewItem *item = 0;
             if (change.isMove() && (item = currentChanges.removedItems.take(change.moveKey(modelIndex + i))))
                 item->index = modelIndex + i;