Your solution just solves my problem. Thank you very much!

I wonder how operations perform when there's a proxy model attached to a source model. It seems that a method (virtual method declared in their parent) is first invoked in the proxy model. If we override the method and did not invoke its parent's one, corresponding method will not be invoked. Actually, it's the QSortFilterProxyModel::method() invokes the corresponding method in source model. Is it right?