iOS: [self.fetchedResultsController PerformFetch:&error];使我的应用程序崩溃

发布于 2024-11-06 08:42:17 字数 1853 浏览 0 评论 0原文

我有一个 UITableViewController，我想向它提供核心数据模型的内容。但是，当我获取内容时，我的应用程序崩溃了。这是 init 方法（我将 NSManagedObjectContext 传递给它）。

- (id)initInManagedObjectContext:(NSManagedObjectContext *)context
{
    self = [super initWithStyle:UITableViewStylePlain];

    if (self) {
        NSFetchRequest *request = [[NSFetchRequest alloc] init];
        request.entity = [NSEntityDescription entityForName:@"Document" inManagedObjectContext:context];
        request.predicate = nil;    
        request.sortDescriptors = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:@"idDoc" 
                                                                                     ascending:YES]];
         /*
         NSError *error = nil;
         NSManagedObject *retrievedDocument = [[context executeFetchRequest:request error:&error] lastObject];
         NSLog(@"retrievedDocument %@", retrievedDocument);
         */

        NSFetchedResultsController *frc = [[NSFetchedResultsController alloc]
                                             initWithFetchRequest:request 
                                             managedObjectContext:context 
                                               sectionNameKeyPath:nil 
                                                        cacheName:@"CollectionCache"];

        self.fetchedResultsController = frc;
        [frc release];
        [request release];


        //HERE IT CRASHES
        NSError *error;
        [self.fetchedResultsController performFetch:&error];

        if (error) {
            // Update to handle the error appropriately.
            NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
            //exit(-1);  // Fail
        }

    }
    return self;
}

我确信上下文已正确传递，因为如果我取消注释注释片段，则存储的数据将正确打印。

我的猜测是 fetchedResultsController 有问题。

谢谢

原文

I have a UITableViewController, and I want to feed it with the content of a core data model.
However, when I fetch the content my app crashes. This is the init method (I pass a NSManagedObjectContext to it).

- (id)initInManagedObjectContext:(NSManagedObjectContext *)context
{
    self = [super initWithStyle:UITableViewStylePlain];

    if (self) {
        NSFetchRequest *request = [[NSFetchRequest alloc] init];
        request.entity = [NSEntityDescription entityForName:@"Document" inManagedObjectContext:context];
        request.predicate = nil;    
        request.sortDescriptors = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:@"idDoc" 
                                                                                     ascending:YES]];
         /*
         NSError *error = nil;
         NSManagedObject *retrievedDocument = [[context executeFetchRequest:request error:&error] lastObject];
         NSLog(@"retrievedDocument %@", retrievedDocument);
         */

        NSFetchedResultsController *frc = [[NSFetchedResultsController alloc]
                                             initWithFetchRequest:request 
                                             managedObjectContext:context 
                                               sectionNameKeyPath:nil 
                                                        cacheName:@"CollectionCache"];

        self.fetchedResultsController = frc;
        [frc release];
        [request release];


        //HERE IT CRASHES
        NSError *error;
        [self.fetchedResultsController performFetch:&error];

        if (error) {
            // Update to handle the error appropriately.
            NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
            //exit(-1);  // Fail
        }

    }
    return self;
}

I'm sure the context is correctly passed because if I uncomment the commented snippet, the stored data are correctly printed.

My guess is that something is wrong with the fetchedResultsController.

thanks

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不喜欢何必死缠烂打 2024-11-13 08:42:17

该异常与您错误使用performFetch：有关：

它返回一个BOOL，告诉您提取是否成功。如果返回“否”，您可以检查 NSError 对象。否则你绝对不能碰它。

可能所有使用 &error 的方法都应该像这样使用：

    NSError *error;
    if (![self.fetchedResultsController performFetch:&error]) {
        // Update to handle the error appropriately.
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        //exit(-1);  // Fail
    }

The exception was related to your wrong use of performFetch:

It returns a BOOL that tells you the success of the fetch. If you get a NO back you are allowed to check the NSError object. Otherwise you must not touch it.

Probably all the methods that use &error should be used like this:

    NSError *error;
    if (![self.fetchedResultsController performFetch:&error]) {
        // Update to handle the error appropriately.
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        //exit(-1);  // Fail
    }

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