WPF DataGrid自定义排序，锁定了一些记录

I have a WPF Datagrid with custom sorting implemented and it works fine. I need to lock some of the records in the collection to Top and Bottom (Top Lock and Bottom Lock). So when a particular record is Top locked, it should be the first record in the collection regardless of any value for the selected column(ie I don't want to sort those rows which are Top locked and Bottom locked). Here is my custom sort method.I have a WPF Datagrid with custom sorting imple