NSFetchedResultsController with > now() doesn't refresh expired entries in swift - ios

Question

I have a UITableview I'm keeping updated with recent items. (That is, added to my CoreData within the last 5 minutes.) I have a field in my Item entity called 'expire_date' which is a Date type. When I download a new item in the background, I add it to CoreData, setting the expire_date to NSDate() plus 5 minutes:
item.expire_date = NSDate(timeIntervalSince1970: NSDate().timeIntervalSince1970+5*60);
My setup for the NSFetchedResultsController looks like:
let fetchRequest=NSFetchRequest(entityName: "Item")
fetchRequest.predicate = NSPredicate(format: "expire_date > now()")
let sortDescriptor = NSSortDescriptor(key: "expire_date")
fetchRequest.sortDescriptors=[sortDescriptor]
myFRC=NSFetchedResultsController(fetchRequest:fetchRequest, managedObjectContext:myMOC)
do {
try myFRC!.performFetch()
} catch {
print(error)
}
The NSFetchedResultsControllerDelegate code is the standard boilerplate for this kind of thing when using a UITableView.
This all works great when starting the app: only existing items that haven't 'timed out' show up. It also works great when new items are added.
The problem is that when an item in the list times out, it doesn't get removed from the results
Anyone have any idea how to accomplish this?

Answer 1

I had the possibility of one or more Items being selected in the UITableView, and I didn't want to lose those selections so I couldn't use W.K.S.'s answer unfortunately. It was strictly speaking correct from the information I had given, although it didn't update the list immediately after any item expires. However, Wain gave me the spark of an idea that worked the way I wanted.
It seems the Item is re-examined by the query when that item is updated, so the trick is to update the item in question when it has expired. I added an NSTimer variable:
var timeoutTimer:NSTimer?
I added a function, addMinimumTimeout() that (re)sets the timeout timer:
func addMinimumTimeout() {
if let _timeoutTimer=timeoutTimer {
_timeoutTimer.invalidate();
timeoutTimer=nil;
}
if myFRC?.fetchedObjects?.count==0 {
return;
}
if let firstItem = myFRC?.fetchedObjects?[0] as? Item {
let timeout=(firstItem.expire_date!.timeIntervalSince1970-NSDate().timeIntervalSince1970)+1.0;
timeoutTimer=NSTimer.scheduledTimerWithTimeInterval(timeout, target: self, selector: #selector(itemTimedOut), userInfo: firstItem, repeats: false);
}
}
My itemTimedOut code looks like this:
func itemTimedOut(timer:NSTimer) {
guard let item=timer.userInfo as? Item else {
return;
}
item.expire_date! = item.expire_date!;
do {
try item.managedObjectContext!.save();
} catch {
let saveError = error as NSError;
print("Error saving: \(saveError)")
return;
}
}
Then in my viewDidLoad, right after I perform my fetch, I call:
addMinimumTimeout();
and I also add it at the end of the boilerplate controller(controller, didChangeObject, atIndexPath, forChangeType, newIndexPath) function.
This way, if there's no items in the list, there's no timeout timer created, but as soon as one is added, the timeout timer is created. When an item is removed for whatever reason, the timer is updated, and if the last one is timed out or removed, there's no timeout timer running.