方法使用NSFetchedResultsController及其委托不工作来移动行

I've been trying to follow this tutorial for rearranging rows in a table view while using NSFetchedResultsController and NSFetchedResultsController delegate, but my project is extremely buggy. What happens is that when I try rearranging a row and drop it, the rows are randomised (probably not randomised, but I can't see the pattern to find the problem). What's wrong with my implementation? tutorial for re