NSFetchedResultsController崩溃对performFetch：当使用缓存时 [英] NSFetchedResultsController crashing on performFetch: when using a cache

问题描述

我使用NSFetchedResultsController来显示一堆使用日期分段的对象。在全新安装时，它一切正常，对象显示在表视图中。但是，似乎当应用程序重新启动时，我得到了崩溃。

I make use of NSFetchedResultsController to display a bunch of objects, which are sectioned using dates. On a fresh install, it all works perfectly and the objects are displayed in the table view. However, it seems that when the app is relaunched I get a crash. I specify a cache when initialising the NSFetchedResultsController, and when I don't it works perfectly.

下面是我创建NSFetchedResultsController的方法：

Here is how I create my NSFetchedResultsController:

- (NSFetchedResultsController *)results {
    // If we are not nil, stop here
    if (results != nil)
        return results;

    // Create the fetch request, entity and sort descriptors
    NSFetchRequest *fetch = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Event" inManagedObjectContext:self.managedObjectContext];
    NSSortDescriptor *descriptor = [[NSSortDescriptor alloc] initWithKey:@"utc_start" ascending:YES];
    NSArray *descriptors = [[NSArray alloc] initWithObjects:descriptor, nil];

    // Set properties on the fetch
    [fetch setEntity:entity];
    [fetch setSortDescriptors:descriptors];

    // Create a fresh fetched results controller
    NSFetchedResultsController *fetched = [[NSFetchedResultsController alloc] initWithFetchRequest:fetch managedObjectContext:self.managedObjectContext sectionNameKeyPath:@"day" cacheName:@"Events"];
    fetched.delegate = self;
    self.results = fetched;

    // Release objects and return our controller
    [fetched release];
    [fetch release];
    [descriptor release];
    [descriptors release];
    return results;
}

这是我在应用崩溃时得到的消息：

These are the messages I get when the app crashes:

FATAL ERROR: The persistent cache of section information does not match the current configuration.  You have illegally mutated the NSFetchedResultsController's fetch request, its predicate, or its sort descriptor without either disabling caching or using +deleteCacheWithName:
*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'FATAL ERROR: The persistent cache of section information does not match the current configuration.  You have illegally mutated the NSFetchedResultsController's fetch request, its predicate, or its sort descriptor without either disabling caching or using +deleteCacheWithName:'

我真的不知道为什么它说，因为我不相信我做任何特别的，会导致这一点。唯一可能的问题是节头（day），我在创建一个新对象时这样构造：

I really have no clue as to why it's saying that, as I don't believe I'm doing anything special that would cause this. The only potential issue is the section header (day), which I construct like this when creating a new object:

// Set the new format
[formatter setDateFormat:@"dd MMMM"];

// Set the day of the event
[event setValue:[formatter stringFromDate:[event valueForKey:@"utc_start"]] forKey:@"day"];

就像我提到的，如果没有缓存，所有这些都很好。任何帮助赞赏！

Like I mentioned, all of this works fine if there is no cache involved. Any help appreciated!

推荐答案

我有一个类似的问题，我的一个应用程序，当苹果发布新的iOS 4.0。
搜索：

I had a similar problem with one of my apps, when the Apple released the new iOS 4.0. Search:

fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:[self managedObjectContext] sectionNameKeyPath:nil cacheName:nil];

并将参数cacheName的值设置为nil。它为我工作，希望它会为你。让我知道。

And set the value of the parameter cacheName to nil. It worked for me, hope it will for you. Let me know.

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