ios - NSManagedObjectContextDidSaveNotification useless? -


i using core data while background contex, , wondering why advise use nsmanagedobjectcontextdidsavenotification merging background main context. created test-project 1 nspersistentstorecoordinator, main context , background context. here code fragment initalisation:

- (nsmanagedobjectcontext *)managedobjectcontext {  if (_managedobjectcontext != nil) {     return _managedobjectcontext; }  nspersistentstorecoordinator *coordinator = [self persistentstorecoordinator]; if (coordinator != nil) {     _managedobjectcontext = [[nsmanagedobjectcontext alloc] initwithconcurrencytype:nsmainqueueconcurrencytype];     [_managedobjectcontext setpersistentstorecoordinator:coordinator]; }  return _managedobjectcontext; }    - (nsmanagedobjectcontext *)backgroundcontext { if (_backgroundcontext != nil) {     return _backgroundcontext; } _backgroundcontext = [[nsmanagedobjectcontext alloc] initwithconcurrencytype:nsprivatequeueconcurrencytype]; _backgroundcontext.persistentstorecoordinator = self.persistentstorecoordinator;  return _backgroundcontext; }

until now, have listened save notification this:

[[nsnotificationcenter defaultcenter] addobserver:self                                          selector:@selector(mergechanges:)                                              name:nsmanagedobjectcontextdidsavenotification                                            object:self.backgroundcontext];

but realised, doesn't matter if merge notification. can edit , save either context, , other 1 get's merged after seconds itself.

so. question, why need nsmanagedobjectcontextdidsavenotification?

your contexts not related. both root contexts attached same persistent store coordinator.

a change persistent store automatically pushed root contexts associated (which why don't need handle nsmanagedobjectcontextdidsavenotification notification.)

nsmanagedobjectcontextdidsavenotification useful when dealing more complex context ancestry, since mid-level context not automatically notify of children when changed.

as example, check out architecture diagram cadmium (https://github.com/jmfieldman/cadmium). when background child context saves writer context, main context must handle nsmanagedobjectcontextdidsavenotification on main thread incorporate updates.


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