Question

我正在使用UIDocument访问核心数据并尝试在后台线程中设置NSFetchedResultsController而不阻止主UI。如果我使用uidocument的managedobjectcontext而不是孩子，它可以工作。我从堆栈溢出中的一个答案中获取了一些代码，但是无法使它与fetchedresultscontroller一起工作。

[ZH peopleDocumentusingBlock:^(UIManagedDocument *peopleDoc){
NSManagedObjectContext *context = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
        context.parentContext = peopleDoc.managedObjectContext;
        [context performBlock:^{
             NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Person"];
           request.sortDescriptors = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:@"key" ascending:YES]];
            [NSFetchedResultsController deleteCacheWithName:nil];
            NSPredicate *predicate = [NSPredicate predicateWithFormat:@"imageurl.length>0"];
            request.predicate = predicate;

            NSError *error = nil;
            if(!self.totalNumberOfPeople) //set total number of people for this fetch used for show more records
            {
                self.totalNumberOfPeople = [context countForFetchRequest:request error:&error]; 
                NSLog(@"total number of people -> %d",self.totalNumberOfPeople);

            }

                self.fetchedResultsController = [[NSFetchedResultsController alloc]initWithFetchRequest:request managedObjectContext:context sectionNameKeyPath:nil cacheName:@"peopleCache"];
dispatch_async(dispatch_get_main_queue(), ^{
                    [self.delegate refreshPeoplelTableview];
                    NSLog(@"fetched objects -> %d",[self.fetchedResultsController.fetchedObjects count]);
                    NSLog(@"total number of people -> %d",self.totalNumberOfPeople);


                });
    }];
}];

实际上context countforfetchrequest但不是fetcheresultscontroller。

提前致谢！

Answer 1

您正在使用“半永久”FRC（它是您的控制器的实例变量），但将其设置为使用“临时”MOC，当没有人再使用它时它将消失。

我不遵循你真正想做的事情，但我认为如果你存储“临时”MOC，它会起作用。但是，您必须首先询问为什么要这样做。

在parentContext和performBlock

之间插入代码

    context.parentContext = peopleDoc.managedObjectContext;
    // Keep the MOC with the FRC...
    self.myBackgroundFetchingMoc = context;
    [context performBlock:^{

使用NSPrivateQueueConcurrencyType从NSManagedObjectContext获取NSFetchedResultsController时为空

1 个答案: