ios - NSFetchedResultsController Called When Not in View -

i have:

• viewcontroller_a
• viewcontroller_b
• viewcontroller_c

where there's nsfetchedresultscontroller powering tableview in b.

my problem can edit b's underlying data while in or c. when edit b's underlying data or c, runs b's delegate function:

func controller(_ controller: nsfetchedresultscontroller<nsfetchrequestresult>, didchange anobject: any, @ indexpath: indexpath?, type: nsfetchedresultschangetype, newindexpath: indexpath?) { 

so appears observer still running, makes sense because never dismissed b. still, delegate function tries update b's tableview , causes crash every time.

i'm new using nsfetchedresultscontroller , appreciate advice on how prevent observer behaving way.