Searching Core Data in Background Thread, Function Terminate Randomly

Question

This is my searching function:

- (void)searchingMethod:(NSString *)aText{
    NSManagedObjectContext *context = [self managedObjectContext];
    NSEntityDescription *entity = [NSEntityDescription 
         entityForName:@"Entity" inManagedObjectContext:context];
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; 
    [fetchRequest setEntity:entity];
    NSPredicate *predicate = [NSPredicate 
          predicateWithFormat:@"word LIKE %@", 
          [searchBar.text lowercaseString]];
    [fetchRequest setPredicate:predicate];
    //fetching array
    NSLog(@"Place 1");
    NSArray *wordArray = [context 
    executeFetchRequest:fetchRequest 
    error:nil];
    NSLog(@"Place 2");

    [self performSelectorOnMainThread:@selector(refreshTableView:) 
                             withObject:wordArray waitUntilDone:NO];
    NSLog(@"Searching End");
}

and I call the searching function with this method:

- (void)searchBar:(UISearchBar *) searchBar textDidChange:(NSString *)Tosearch{
if([[searchBar text] length] >0)
{
    NSThread *aThread = [[NSThread alloc] 
        initWithTarget:self 
        selector:@selector(searchingMethod:) 
        object:searchBar.text];
    [aThread start];
}
else
{ 
    //others...
}
return;
}

Normally, I would get such result：

2012-07-05 00:04:46.706 MyApp[2376:207] Place 1
2012-07-05 00:04:46.783 MyApp[2376:207] Place 2
2012-07-05 00:04:46.823 MyApp[2376:207] searching End

After performed the searching method a dozen times, it stops at this position.

2012-07-05 00:11:42.174 MyApp[2376:207] Place 1

Continue to search several times, it returned to normal. And then odd again... It makes me puzzled.

I've spent many days to try different multi-thread methods, the result is still the same.
Please help me out! Thank you!

Did you create the NSManagedContext `context` on that background thread? — Florian Mielke, Jul 05 '12 at 05:19
I have read Apple's document [Concurrency with Core Data](http://developer.apple.com/library/ios/#documentation/cocoa/conceptual/coredata/Articles/cdConcurrency.html#//apple_ref/doc/uid/TP40003385-SW1) but yet have no idea how to create NSManagedObjectContext using objectWithID: — Jimi, Jul 05 '12 at 14:26

score 2 · Answer 1 · answered Jul 05 '12 at 05:51

2

Core Data is not thread safe. You need to create your own NSManagedObjectContext on the background thread. With that you can do your searching in the background. You then cannot simply send the managed objects directly to the main thread. You have to ship the object IDs over and on the main thread get the objects for them from the main context using its objectWithID: method.

answered Jul 05 '12 at 05:51

Sven

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Thank you Sven! I have revised my question and added the codes with which I create NSManagedObjectContext. And I also try to create NSManagedObjectContext using objectID but failed. would you like to show me a little sample codes? – Jimi Jul 05 '12 at 13:40

Searching Core Data in Background Thread, Function Terminate Randomly

1 Answers1