NSFetchedResultsController数据未更新

问题描述

我正在制作一个从服务器获取产品列表的应用程序。然后将它们存储在Core Data数据库中，并使用呈现它们，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NSFetchedResultsControllerDelegate方法。如何正确更新gridView？

I'm making an app which fetches a list of products from a server. I then store them in a Core Data database and I present them using GMGridView and the datasource is a NSFetchedResultsController. When I change the product details in the server, I want my iOS app to synchronize and make the necessary changes so I implement the NSFetchedResultsControllerDelegate method. How should I update my gridView properly?

- (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;
        }
}

一些详细信息：

_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来修改不同类中的CoreData，相同的本地网址。

I make the CoreData changes in a different class by modifying the same UIManagedDocument alloc,init-ed from the same local URL.

但是，我遇到了两个重要问题：

However, I get 2 important problems:

• 更新数据库中的项目（例如更改产品名称或价格），但更改不会反映在UI中，即我无法正确重新加载我的GMGridViewCell。 （注意与上面的重新加载相关的代码）


• 大多数时候，我在服务器上更新的产品在数据库中复制，虽然我有一个机制来防止这样的错误。 （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，我只是修改其详细信息）。以下是代码：

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];
}

推荐答案

到 NSManagedObjectContextDidSaveNotification ，我必须合并在后台线程中修改的上下文中的更改和主线程中的更改。我从这个中选择的答案得到了想法

Turns out I have to listen to NSManagedObjectContextDidSaveNotification and I have to merge the changes in the context modified in the background thread and the one in the main thread. I got the idea from the chosen answer in this question

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

//上下文中的更改必须合并

//Then the changes in the context has to be merged

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

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