Fix QQmlDelegateModel ignoring layoutChange in certain situations

Fix a regression introduced by commit a0aefe1 which caused the model to
ignore layout changes if d->m_adaptorModel.rootIndex was just a descendant
of any of the parent indexes, or when no parent indexes at all were provided
in the notification.

Task-number: QTBUG-39492
Change-Id: I4c97929d25ef75947ccfcbbe5bc234096689c58d
Reviewed-by: Alan Alpert <aalpert@blackberry.com>

2 files changed, 18 insertions, 2 deletions

diff --git a/src/qml/types/qqmldelegatemodel.cpp b/src/qml/types/qqmldelegatemodel.cpp
index 4591d42710..6029e277dd 100644
--- a/src/qml/types/qqmldelegatemodel.cpp
+++ b/src/qml/types/qqmldelegatemodel.cpp
@@ -1521,6 +1521,18 @@ void QQmlDelegateModel::_q_dataChanged(const QModelIndex &begin, const QModelInd
         _q_itemsChanged(begin.row(), end.row() - begin.row() + 1, roles);
 }
 
+bool QQmlDelegateModel::isDescendantOf(const QPersistentModelIndex& desc, const QList< QPersistentModelIndex >& parents) const
+{
+    for (int i = 0, c = parents.count(); i < c; ++i) {
+        for (QPersistentModelIndex parent = desc; parent.isValid(); parent = parent.parent()) {
+            if (parent == parents[i])
+                return true;
+        }
+    }
+
+    return false;
+}
+
 void QQmlDelegateModel::_q_layoutAboutToBeChanged(const QList<QPersistentModelIndex> &parents, QAbstractItemModel::LayoutChangeHint hint)
 {
     Q_D(QQmlDelegateModel);
@@ -1529,8 +1541,9 @@ void QQmlDelegateModel::_q_layoutAboutToBeChanged(const QList<QPersistentModelIn
 
     if (hint == QAbstractItemModel::VerticalSortHint) {
         d->m_storedPersistentIndexes.clear();
-        if (!parents.contains(d->m_adaptorModel.rootIndex))
+        if (!parents.isEmpty() && d->m_adaptorModel.rootIndex.isValid() &&  !isDescendantOf(d->m_adaptorModel.rootIndex, parents)) {
             return;
+        }
 
         for (int i = 0; i < d->m_count; ++i) {
             const QModelIndex index = d->m_adaptorModel.aim()->index(i, 0, d->m_adaptorModel.rootIndex);
@@ -1550,8 +1563,9 @@ void QQmlDelegateModel::_q_layoutChanged(const QList<QPersistentModelIndex> &par
         return;
 
     if (hint == QAbstractItemModel::VerticalSortHint) {
-        if (!parents.contains(d->m_adaptorModel.rootIndex))
+        if (!parents.isEmpty() && d->m_adaptorModel.rootIndex.isValid() && !isDescendantOf(d->m_adaptorModel.rootIndex, parents)) {
             return;
+        }
 
         for (int i = 0, c = d->m_storedPersistentIndexes.count(); i < c; ++i) {
             const QPersistentModelIndex &index = d->m_storedPersistentIndexes.at(i);
diff --git a/src/qml/types/qqmldelegatemodel_p.h b/src/qml/types/qqmldelegatemodel_p.h
index 0b67179163..53cc94bbdf 100644
--- a/src/qml/types/qqmldelegatemodel_p.h
+++ b/src/qml/types/qqmldelegatemodel_p.h
@@ -143,6 +143,8 @@ private Q_SLOTS:
     void _q_layoutChanged(const QList<QPersistentModelIndex>&, QAbstractItemModel::LayoutChangeHint);
 
 private:
+    bool isDescendantOf(const QPersistentModelIndex &desc, const QList<QPersistentModelIndex> &parents) const;
+
     Q_DISABLE_COPY(QQmlDelegateModel)
 };