ios - Core Data - NSManagedObjectContext returns nil in Master-Detail Application -

i'm working on alarm clock app, use core data stack apple's master-detail application template, worked fine core data, until i'm calling in - (void)applicationdidenterbackground:(uiapplication *)application method masterviewcontroller work during app in background , should tableview [self.tableview reloaddata].

and point error

+entityforname: nil not legal nsmanagedobjectcontext parameter searching entity name 'myentity'

everything works fine when app running when tableview should reload when application in background error. knows how solve problem?

in appdelegate.m

- (nsmanagedobjectcontext *)managedobjectcontext { if (_managedobjectcontext != nil) return _managedobjectcontext;  nspersistentstorecoordinator *coordinator = [self persistentstorecoordinator]; if (coordinator != nil) {      _managedobjectcontext = [[nsmanagedobjectcontext alloc] init];     [_managedobjectcontext setpersistentstorecoordinator:coordinator]; } return _managedobjectcontext; } 

i have code in applicationdidfinishlaunchingwithoptions method:

//some other stuff before... wkmasterviewcontroller *controller = (wkmasterviewcontroller *)navigationcontroller.topviewcontroller; controller.managedobjectcontext = self.managedobjectcontext; 

in masterviewcontroller.m have following code:

- (nsfetchedresultscontroller *)fetchedresultscontroller { if (_fetchedresultscontroller != nil) {     return _fetchedresultscontroller; }  nsfetchrequest *fetchrequest = [[nsfetchrequest alloc] init]; nsentitydescription *entity = [nsentitydescription entityforname:@"myentity" inmanagedobjectcontext:self.managedobjectcontext]; [fetchrequest setentity:entity];  [fetchrequest setfetchbatchsize:20];  nssortdescriptor *sortdescriptor = [[nssortdescriptor alloc] initwithkey:@"zeit" ascending:no]; nsarray *sortdescriptors = @[sortdescriptor];  [fetchrequest setsortdescriptors:sortdescriptors];  nsfetchedresultscontroller *afetchedresultscontroller = [[nsfetchedresultscontroller alloc] initwithfetchrequest:fetchrequest managedobjectcontext:self.managedobjectcontext sectionnamekeypath:nil cachename:@"master"]; afetchedresultscontroller.delegate = self; self.fetchedresultscontroller = afetchedresultscontroller;  nserror *error = nil; if (![self.fetchedresultscontroller performfetch:&error]) {     nslog(@"unresolved error %@, %@", error, [error userinfo]);     abort(); }  return _fetchedresultscontroller; }     

thanks!!

check-> function

- (nsmanagedobjectcontext *)managedobjectcontext {} 

is returning nil _managedobjectcontext?

if variable context nil. means managedobjectcontext method not working correctly.