How do I save QStandardItemModel's checkState

[lni]

Hello, I need to save QStandardItemModel, which is fine. But I also need to save each item's checkState of the model separately. How can I do that? I am getting QModelIndex of each item, but the QModelIndex is related to its parent, for instance, in the attachment, item11 and item21 have same index.row() and index.column(). The QModelIndex::internalPointer() can't really be used when saving to a file...

Help is very much appreciated!