核心数据：获取结果控制器导致过度发布/崩溃

Question

我正在使用core data，并且有一个UITableViewController，它从core data 加载数据。这是modal view，如果我第三次加载模态视图，它会因EXC_BAD_ACCESS 而崩溃。

- (NSFetchedResultsController *)fetchedResultsController {

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

    // Create and configure a fetch request
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Ride" inManagedObjectContext:managedObjectContext];
    [fetchRequest setEntity:entity];

    // Create the sort descriptors array
    NSSortDescriptor *sectionTitle = [[NSSortDescriptor alloc] initWithKey:@"dateStart" ascending:NO];
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sectionTitle, nil];
    [fetchRequest setSortDescriptors:sortDescriptors];

    // Create and initialize the fetch results controller
    NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:managedObjectContext sectionNameKeyPath:nil cacheName:@"Root"];
    self.fetchedResultsController = aFetchedResultsController;
    fetchedResultsController.delegate = self;

    // Memory management
    [aFetchedResultsController release];
    [fetchRequest release];
    [sectionTitle release];
    [sortDescriptors release];

    return fetchedResultsController;

}//end

崩溃表明它来自这一行：

NSEntityDescription *entity = [NSEntityDescription entityForName:@"Ride" inManagedObjectContext:managedObjectContext];

这是在 viewDidLoad 中：

if (managedObjectContext == nil) { 
        managedObjectContext = [MyAppDelegate instance].managedObjectContext; 
    }

呈现模态视图：

History *history = [[[History alloc] init] autorelease];
UINavigationController *nav = [[[UINavigationController alloc] initWithRootViewController:history] autorelease];
[self presentModalViewController:nav animated:YES];

关闭模式：

- (void)done {
    [self dismissModalViewControllerAnimated:YES];
}

提供 EXC_BAD_ACCESS 的堆栈跟踪：

现在，为了使用核心数据设置此视图，我遵循Core Data Books 示例项目，我的代码看起来几乎相同。为什么模态视图加载几次后会崩溃？

Answer 1

好的，我想通了，我的 managedObjectContext 没有被保留，因为我没有使用 self.所以，我通过这样做来修复它：

// Core Data
if (managedObjectContext == nil) { 
    self.managedObjectContext = [MyAppDelegate instance].managedObjectContext; 
}