iphone - 数据未更新的 NSFetchedResultsController

Question

我正在制作一个从服务器获取产品列表的应用程序。然后我将它们存储在核心数据数据库中，并使用 GMGridView 呈现它们并且数据源是 NSFetchedResultsController。当我更改服务器中的产品详细信息时，我希望我的 iOS 应用程序同步并进行必要的更改，因此我实现了 NSFetchedResultsControllerDelegate 方法。我应该如何正确更新我的 gridView？

- (void)controller:(NSFetchedResultsController *)controller
   didChangeObject:(id)anObject
       atIndexPath:(NSIndexPath *)indexPath
     forChangeType:(NSFetchedResultsChangeType)type
      newIndexPath:(NSIndexPath *)newIndexPath
{
        switch(type)
        {
            case NSFetchedResultsChangeInsert:
                [_currentData insertObject:anObject atIndex:newIndexPath.row];
                [_currentData removeObjectAtIndex:indexPath.row];
                [_gmGridView insertObjectAtIndex:newIndexPath.row animated:YES];
                [_gmGridView removeObjectAtIndex:indexPath.row animated:YES];

                [_gmGridView reloadObjectAtIndex:newIndexPath.row animated:YES];
                [_gmGridView reloadObjectAtIndex:indexPath.row animated:YES];

                [_gmGridView reloadData];

                //[self updatePageControl];
                break;

            case NSFetchedResultsChangeDelete:
                [_currentData removeObjectAtIndex:indexPath.row];

                [_gmGridView removeObjectAtIndex:indexPath.row animated:YES];
                //[self updatePageControl];
                [_gmGridView reloadInputViews];
                [_gmGridView reloadData];

                break;

            case NSFetchedResultsChangeUpdate:
                [_gmGridView reloadObjectAtIndex:indexPath.row animated:YES];

                ////////might be irrelevant, but just trying it out
                [_currentData insertObject:anObject atIndex:newIndexPath.row];
                [_currentData removeObjectAtIndex:indexPath.row];
                [_gmGridView insertObjectAtIndex:newIndexPath.row animated:YES];
                [_gmGridView removeObjectAtIndex:indexPath.row animated:YES];

                [_gmGridView reloadObjectAtIndex:newIndexPath.row animated:YES];
                [_gmGridView reloadObjectAtIndex:indexPath.row animated:YES];

                ////////


                [_gmGridView reloadInputViews];
                [_gmGridView reloadData];

                break;

            case NSFetchedResultsChangeMove:
                [_currentData removeObjectAtIndex:indexPath.row];
                [_currentData insertObject:anObject atIndex:newIndexPath.row];
                [_gmGridView removeObjectAtIndex:indexPath.row animated:YES];
                [_gmGridView insertObjectAtIndex:newIndexPath.row animated:YES];

                [_gmGridView reloadInputViews];

                [_gmGridView reloadData];

                break;
        }
}

一些细节:

_currentData = [[self.fetchedResultsController fetchedObjects]mutableCopy];
//I did this because previously I wasn't using a fetchedResultsController but a NSMutableArray instead. I know that it's inefficient (because I have 2 models) but this is the simplest implementation I want to do now. 

我通过修改相同的 UIManagedDocument alloc，在不同的类中更改 CoreData，从相同的本地 URL 初始化。

但是，我遇到了 2 个重要问题:

• 数据库中的项目已更新(例如，更改产品名称或价格)但更改未反射(reflect)在用户界面中，即我无法正确重新加载我的 GMGridViewCell。 (注意上面reload相关的代码)
• 大多数时候，我在服务器中更新的产品在数据库中是重复的，尽管我有防止此类错误的机制。 (在创建产品之前，我首先使用唯一标识符搜索现有产品。如果有现有产品，我只需修改其详细信息)。这是代码:

---

NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Product"];        

request.predicate = [NSPredicate predicateWithFormat:@"product_id = %@", [imonggoInfo   objectForKey:PRODUCT_ID]];    

NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES];    

request.sortDescriptors = [NSArray 

arrayWithObject:sortDescriptor];  NSError *error = nil;  

NSArray *matches = [context executeFetchRequest:request error:&error];

if (!matches | ([matches count] > 1)){
    //handle error
}else if ([matches count] == 0){
    //make a new product
}else{
    //return existing
    item = [matches lastObject];
}

Answer 1

原来我必须听取 NSManagedObjectContextDidSaveNotification 并且我必须合并在后台线程和主线程中修改的上下文中的更改。我从这个 question 中选择的答案中得到了这个想法

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(contextChanged:) name:NSManagedObjectContextDidSaveNotification object:nil];

//那么上下文的变化就得合并

- (void)contextDidSave:(NSNotification*)notification{
    NSLog(@"contextDidSave Notification fired.");
    SEL selector = @selector(mergeChangesFromContextDidSaveNotification:);
    [self.itemDatabase.managedObjectContext performSelectorOnMainThread:selector withObject:notification waitUntilDone:NO]; 
}