Question

我正在使用iOS上的xmpp框架进行聊天应用程序，我正在使用框架本身提供的名册存储，我在运行应用程序时使用我的帐户登录时收到此错误，它突然崩溃，我试图调试它，但我无法找到解释。这是代码：

@interface FriendListTableViewController ()<NSFetchedResultsControllerDelegate>
@property (nonatomic,strong) NSFetchedResultsController *fetchedResultController;

@end

@implementation FriendListTableViewController


-(AppDelegate *)appDelegate
{
    return (AppDelegate *)[[UIApplication sharedApplication]delegate];
}

#pragma mark - FetchedResult Controller delegate

-(NSFetchedResultsController *)fetchedResultController
{
    if (self.fetchedResultController == nil) { //Here is the EXC_BAD_ACCESS code=2

        NSManagedObjectContext *moc = [[self appDelegate] managedObjectContext_roster];

        NSEntityDescription *entity = [NSEntityDescription entityForName:@"XMPPUserCoraDataStorageObject" inManagedObjectContext:moc];

        NSSortDescriptor *sortDes1 = [[NSSortDescriptor alloc] initWithKey:@"sectionNum" ascending:YES];

        NSSortDescriptor *sortDes2 = [[NSSortDescriptor alloc] initWithKey:@"displayName" ascending:YES];

        NSArray *sortDescriptors = [NSArray arrayWithObjects:sortDes1,sortDes2, nil];

        NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
        [fetchRequest setEntity:entity];
        [fetchRequest setSortDescriptors:sortDescriptors];
        [fetchRequest setFetchBatchSize:10];

        self.fetchedResultController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:moc sectionNameKeyPath:@"sectionNum" cacheName:nil];

        [self.fetchedResultController setDelegate:self];

        NSError *error = nil;

        if (![self.fetchedResultController performFetch:&error]) {

        }

    }

    return self.fetchedResultController;
}

希望你能帮助我。

Answer 1

您正在编写一个getter方法，fetchedResultController（虽然我会将其命名为fetchedResultsController，以匹配类名。然后在该getter方法中，您调用self.fetchedResultController（重新调用内部的getter）以及稍后self.fetchedResultController = ...，在getter中调用setter。

在setter / getter方法中，你应该直接使用支持ivar。

更好的习语：在.h：

@property (nonatomic, strong) NSFetchedResultsController *fetchedResultsController

然后在.m

-(NSFetchedResultsController *)fetchedResultsController
{
    if (_!fetchedResultsController) {

        NSManagedObjectContext *moc = self.managedObjectContext_roster;

        NSEntityDescription *entity = [NSEntityDescription entityForName:@"XMPPUserCoraDataStorageObject" inManagedObjectContext:moc];

        NSSortDescriptor *sortDes1 = [[NSSortDescriptor alloc] initWithKey:@"sectionNum" ascending:YES];

        NSSortDescriptor *sortDes2 = [[NSSortDescriptor alloc] initWithKey:@"displayName" ascending:YES];

        NSArray *sortDescriptors = @[sortDes1, sortDes2];

        NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
        [fetchRequest setEntity:entity];
        [fetchRequest setSortDescriptors:sortDescriptors];
        [fetchRequest setFetchBatchSize:10];

        _fetchedResultsController = [[NSFetchedResultsController alloc] 
                              initWithFetchRequest:fetchRequest
                              managedObjectContext:moc          
                                sectionNameKeyPath:@"sectionNum" 
                                        cacheName:nil];

        _fetchedResultsController.delegate = self;

        NSError *error = nil;

        if (![_fetchedResultsController performFetch:&error]) {
              NSAssert(NO, @"fetchedResultsController fetch failed");
        }

    }

    return _fetchedResultsController;
}

其他几点说明：我对数组初始化语法进行了现代化。我还建议你将MOC参考保留在本地，而不是回到应用代表那里找到它。混合使用点和括号表示法会使您的代码难以阅读;考虑fetchRequest.entity = entity等等。最后，在代码中使用那些硬编码的字符串密钥路径（sectionNum，XMPPUserCoreDataStorageObject等）是一个难以发现的错误。将它们定义为extern个字符串。

NSFetchedResultController EXC_BAD_ACCESS代码2

1 个答案: