Insert before next item when it exists

Something is off about the way the last child of previous item is
calculated, but we can work-around that by just using the next element
when it exist. In the case there isn't a next element, we will hit the
fallback in 'last child of previous' and insert at the end anyway.

Fixes: QTBUG-66062
Change-Id: Iced69d52c4587434ffdbb09b08b3441289f34eba
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@qt.io>

1 files changed, 9 insertions, 2 deletions

diff --git a/src/controls/Private/qquicktreemodeladaptor.cpp b/src/controls/Private/qquicktreemodeladaptor.cpp
index d2ed42b2d..287b388fd 100644
--- a/src/controls/Private/qquicktreemodeladaptor.cpp
+++ b/src/controls/Private/qquicktreemodeladaptor.cpp
@@ -362,8 +362,15 @@ void QQuickTreeModelAdaptor1::showModelChildItems(const TreeItem &parentItem, in
     if (start == 0) {
         startIdx = rowIdx;
     } else {
-        const QModelIndex &prevSiblingIdx = m_model->index(start - 1, 0, parentIndex);
-        startIdx = lastChildIndex(prevSiblingIdx) + 1;
+        // Prefer to insert before next sibling instead of after last child of previous, as
+        // the latter is potentially buggy, see QTBUG-66062
+        const QModelIndex &nextSiblingIdx = m_model->index(end + 1, 0, parentIndex);
+        if (nextSiblingIdx.isValid()) {
+            startIdx = itemIndex(nextSiblingIdx);
+        } else {
+            const QModelIndex &prevSiblingIdx = m_model->index(start - 1, 0, parentIndex);
+            startIdx = lastChildIndex(prevSiblingIdx) + 1;
+        }
     }
 
     int rowDepth = rowIdx == 0 ? 0 : parentItem.depth + 1;