How to “touch” a Core Data entity, to trigger NSFetchedResultsController?

问题

Say you have a core data entity,

public class CDPerson: NSManagedObject

You get new info from the net ... a field changes,

p.name = 'Debbie'

That CDPerson item is "touched" and hence,

your NSFetchedResultsController will trigger,

perfect.

But say CDPerson can belong to CDAddress

In core data, a change in CDAddress does not trigger a change in CDPerson

But. When an address is touched, you DO want to touch the relevant person items,

so that results controllers will know CDPerson has been changed.

How to "touch" a cd entity?

One rubbish solution, assuming you have an unimportant field,

let touch = p.creationDate
p.creationDate = touch

Alternately you could add an Int64 and

p.touchyInt = a random number, or increment, etc

These are poor solutions

Is there actually a way to "touch" a core data entity, for results controllers?

This seems to be critical in propagating changes in related entities.

It's hard to believe there is no solution for this.

回答1:

Core Data recognizes changes by the firing of -willChangeValueForKey: and -didChangeValueForKey: as the comment from @pbasdf indicated. You can call only -didChangeValueForKey: if you want but I would really do both.

Those calls also work on relationships. So in your Address object, you can touch both the value to be changed and the relationship to the person:

- (void)setCity:(NSString*)cityString
{
  [self willChangeValueForKey:@"city"];
  [self willChangeValueForKey:@"person"];
  _city = cityString;
  [self didChangeValueForKey:@"person"];
  [self didChangeValueForKey:@"city"];
}

With an end result of the NSFetchedResultsController being told that the associated person object has changed and the cell should be re-drawn.

来源：https://stackoverflow.com/questions/60277521/how-to-touch-a-core-data-entity-to-trigger-nsfetchedresultscontroller