Qt::QAbstractItemModel::beginRemoveRows() crash - c++

Question

I have a problem with implementation of custom model (base class is QAbstractItemModel) for QTreeView.
In a nutshell, after calling of beginRemoveRows(), QAbstractItemModel calls my implementation of parent() with QModelIndex that returns dangling pointer from QModelIndex::internalPointer(). Here is call stack:
Ok, posting as small part of code as possible..
I'm working with next tree:
Here are solutions that contain projects that contain files.
Model contains instances of FileItem class:
class FileItem;
typedef QSharedPointer<FileItem> FileItemPtr;
class FileItem
{
public:
explicit FileItem(File* file, FileItem* parentItem = nullptr);
...
FileItem* child(int row); // returns #row element of #childItems_ vector
FileItem* parentItem() const; // returns #parentItem_
void removeChild(int row); // removes #row element from #childItems_ vector
private:
QVector<FileItemPtr> childItems_;
FileItem* parentItem_;
...
};
Here is model's (FilesModel) main functions:
class FilesModel :
public QAbstractItemModel
{
...
private:
QModelIndex index(
int row,
int column = 0,
const QModelIndex& parent = QModelIndex()) const Q_DECL_OVERRIDE;
bool removeRows(int row, int count, const QModelIndex& parent = QModelIndex()) Q_DECL_OVERRIDE;
QModelIndex parent(const QModelIndex& index) const Q_DECL_OVERRIDE;
// returns corresponding childCount() for valid #parent's internalPointer()
int rowCount(const QModelIndex& parent = QModelIndex()) const Q_DECL_OVERRIDE;
int columnCount(const QModelIndex& parent = QModelIndex()) const Q_DECL_OVERRIDE
{
Q_UNUSED(parent);
return 1;
}
private:
QVector<FileItemPtr> items_;
}
QModelIndex's creation:
QModelIndex FilesModel::index(
int row,
int column /*= 0*/,
const QModelIndex& parent /*= QModelIndex()*/) const
{
if(!hasIndex(row, column, parent))
return invalidIndex();
if(!parent.isValid()) // If, parent is invalid, then #row is our items_[row]
{
if(row < items_.size())
{
FileItem* item = items_.value(row).data();
// Pass #item as QModelIndex's internal pointer
return createIndex(row, column, item);
}
return invalidIndex();
}
FileItem* parentItem = static_cast<FileItem*>(parent.internalPointer());
FileItem* childItem = parentItem->child(row);
if(childItem)
// Pass #childItem as QModelIndex's internal pointer
return createIndex(row, column, childItem);
else
return invalidIndex();
}
Getting parent of item:
QModelIndex FilesModel::parent(const QModelIndex& index) const
{
if(!index.isValid())
return invalidIndex();
FileItem* childItem = static_cast<FileItem*>(index.internalPointer());
///////////////////////////////////////////////////////////////////////////
//
// #childItem is dandling poiner after call of beginRemoveRows()
// for root item. See FilesModel::removeRows()
//
FileItem* parentItem = childItem->parentItem();
if(parentItem == nullptr)
return invalidIndex();
return createIndex(parentItem->row(), 0, parentItem);
}
FilesModel::removeRows()
Ok, next impl of FilesModel::removeRows() works fine in case, when i try to remove any file (sub item of project) and any project (sub item of solution). But, when I'm removing solution item (on of roots element of view), I have the situation, that was described on the beginning of question: QAbstractItemModel calls parent() function with QModelIndex that returns dangling pointer from QModelIndex::internalPointer(), but I'm passing valid pointers to createIndex() and never use explicit deletion of QModelIndex::internalPointer().
Ok, here is items removing:
bool FilesModel::removeRows(int row, int count, const QModelIndex& parent /*= QModelIndex()*/)
{
Q_ASSERT(count > 0);
Q_ASSERT(row >= 0);
if(parent.isValid()) // Child items of #items_
{
// This branch works fine
for(int r = row; r < (row + count); ++r)
{
QModelIndex idxRemove = parent.child(r, 0);
Q_ASSERT(idxRemove.isValid());
FileItem* fiRemove = static_cast<FileItem*>(idxRemove.internalPointer());
Q_ASSERT(fiRemove);
if(idxRemove.child(0, 0).isValid()) // Has childrens
{
bool childRemoved = removeRows(0, fiRemove->childCount(), idxRemove);
Q_ASSERT(childRemoved);
}
}
FileItem* fiParent = static_cast<FileItem*>(parent.internalPointer());
Q_ASSERT(fiParent->childCount() >= (row + count - 1));
beginRemoveRows(parent, row, row + count - 1);
int childToRemove = row;
for(int r = row; r < (row + count); ++r)
fiParent->removeChild(childToRemove);
endRemoveRows();
return true;
}
else // Removing #items_
{
// Here is problem branch
Q_ASSERT(rowCount() >= (row + count - 1));
for(int r = row; r < (row + count); ++r)
{
FileItem* slnItem = items_.value(r).data();
bool projectRemoved = removeRows(0, slnItem->childCount(), index(r));
Q_ASSERT(projectRemoved);
}
///////////////////////////////////////////////////////////////////////
// This call to beginRemoveRows() cause call of parent() function
// with invalid QModelIndex::internalPointer()
//
beginRemoveRows(QModelIndex(), row, row + count - 1);
int slnRemove = row;
for(int r = row; r < (row + count); ++r)
items_.remove(slnRemove);
endRemoveRows();
return true;
}
return false;
}
Any one know what is the problem ?
I'm working with this model with one, GUI thread. I have Qt 5.4.0 on Windows.
Thanks
UPDATE:
validateItem() just checks the pointer value to catch the problem with dandling pointer from QModelView::internalPointer()
void FileItem::validateItem() const
{
Q_ASSERT((reinterpret_cast<size_t>(this) > 0x1000)
&& "Invalid item");
for(const FileItemPtr& child : childItems_)
child->validateItem();
}
So, for finding the problem my FilesModel::parent() looks like this:
QModelIndex FilesModel::parent(const QModelIndex& index) const
{
if(!index.isValid())
return invalidIndex();
FileItem* childItem = static_cast<FileItem*>(index.internalPointer());
#if !defined(NDEBUG)
// Try to understand, if #childItem is OK
childItem->validateItem();
#endif
...
}

Answer 1

Call stack you are showing is indicating that assertion from YOUR CODE is failing, so you should be aware what is the problem!
Check your code in FileItem::validateItem line nr 316 to see what is the problem. (Just click proper (second) item in call stack view when crash occurs again)
referring to update:
UPDATE: validateItem() just checks the pointer value to catch the
problem with dandling pointer from QModelView::internalPointer()
Q_ASSERT((reinterpret_cast(this) > 0x1000)
WTF? Who told you that this is proper way to detect that? Dangling pointer doesn't mean that pointer has some specific value!