Question

我是iOS的初学者。当我将Core Data用于我的示例项目时，它会给我一个线程错误。

请帮我解决这个错误。

这是我的代码：

-(NSFetchedResultsController*)fetchedResultController{
if (self.fetchedResultController != nil ) {
    return self.fetchedResultController;
}

NSFetchRequest *request = [[NSFetchRequest alloc]init];
NSManagedObjectContext *context = [self managedObjectContext];

NSEntityDescription *entity = [NSEntityDescription insertNewObjectForEntityForName:@"Recepie" inManagedObjectContext:context];

[request setEntity:entity];

NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc]initWithKey:@"recepieName" ascending:YES];

NSArray *sortDescriptorArray = [[NSArray alloc]initWithObjects:sortDescriptor,nil];

request.sortDescriptors = sortDescriptorArray;

self.fetchedResultController = [[NSFetchedResultsController alloc] initWithFetchRequest: request managedObjectContext:context sectionNameKeyPath:nil cacheName:nil];

self.fetchedResultController.delegate = self;

return self.fetchedResultController;

}

Answer 1

使用像这样的点符号引用属性时

if (self.fetchedResultController != nil ) {
    return self.fetchedResultController;
}

它等同于调用[self fetchedResultController]方法（这是此属性的getter）。当你这样做时，你已经在getter中，所以该方法无限调用自身，导致Stack overflow error。

您不应使用点表示法来获取属性值（使用setter是正常的）。改为使用backing variable：

if(_fetchedResultController != nil) {
    return _fetchedResultController;
}

Answer 2

您能否请尝试以下代码。

  -(NSFetchedResultsController*)fetchedResultController{
   if (self.fetchedResultController != nil ) {
        return self.fetchedResultController;
    }

   NSFetchRequest *request = [[NSFetchRequest alloc]init];
   NSManagedObjectContext *context = [self managedObjectContext];

   NSEntityDescription *entity = [NSEntityDescription insertNewObjectForEntityForName:@"Recepie" inManagedObjectContext:context];

   [request setEntity:entity];

    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc]initWithKey:@"recepieName"  ascending:YES];

    NSArray *sortDescriptorArray = [[NSArray alloc]initWithObjects:sortDescriptor,nil];

    request.sortDescriptors = sortDescriptorArray;

    self.fetchedResultController = [[NSFetchedResultsController alloc] initWithFetchRequest:    request managedObjectContext:context sectionNameKeyPath:nil cacheName:nil];

    self.fetchedResultController.delegate = self;

    error = nil;

    if (![self.fetchedResultsController performFetch:&error]) {
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }

   return self.fetchedResultController;
}

以下代码中的错误是什么？

2 个答案: