CODEWITHSUNDEEP
cocoacore-data
the Reverend
the Reverend

Reputation: 12559

Executing a fetch request on another thread

I want to make a CoreData fetch request on a background thread in order to give the user the option to cancel it.

Below is my background thread code:

- (void)searchDailyNotes
{
    NSEntityDescription *entity = [NSEntityDescription
            entityForName:@"DailyNotes"
            inManagedObjectContext:self.managedObjectContext];

    NSString *searchString = [self.searchTextField stringValue];
    NSFetchRequest *fetchRequest= [[NSFetchRequest alloc] init];
    NSPredicate *predicate = [NSPredicate
            predicateWithFormat:@"notes contains[cd] %@", searchString];
    [fetchRequest setEntity:entity];
    [fetchRequest setPredicate:predicate];

    NSError *error = nil;
    [_dailyNotesArray addObjectsFromArray:
            [self.managedObjectContext
             executeFetchRequest:fetchRequest
             error:&error]];

    NSLog(@"dailynotesArray count: %lu", [_dailyNotesArray count]);
    if(error){
        [NSApp presentError:error];
    }
    [fetchRequest release];
}

Questions:

Upvotes: 1

Views: 575

Answers (1)

Tom Harrington
Tom Harrington

Reputation: 70956

Cocoa threading doesn't generally include the idea of forcing a thread to abort. You'll see a cancel method, but that's strictly advisory. The idea is that the code in the thread will check this state periodically and exit early if a cancel has been requested. You'll see this in NSThread and NSOperation, for example. If the code doesn't check for a cancel request, the cancel method has no effect.

Because of that, you'll need to add checks for a cancel request if you want to handle cancellation. If you see that a cancel was requested, you can do whatever cleanup you need before actually finishing the thread. But you can't interrupt the fetch request in progress anyway-- once you've called the method to start it, you wait until it finishes.

On a separate note, how long do your fetches take that you actually need to worry about this situation?

Upvotes: 1

Related Questions