Question

我在Core Data上使用Justin Driscoll's article，使用单例模式的UIManagedDocument为UITabViewController设置它。我在模拟器上运行应用程序。它第一次正常工作。数据库创建成功，我可以在tableview控制器中查看每个选项卡的数据。但是，当我重新启动应用程序时，应用程序崩溃并出现错误

    Assertion failure in -[UIManagedDocument openWithCompletionHandler:],
     ** Terminating app due to uncaught exception 'NSInternalInconsistencyException',
    reason: 'attempt to open or a revert document that already has an open or revert 
    operation in flight

导致崩溃的代码。我使用NSLog语句进行了一些调试。

   if (![[NSFileManager defaultManager] fileExistsAtPath:[self.document.fileURL path]]) {
        NSLog(@"document doesnot exist and hence START CREATING");
        [self dataIntoDocument:self.document];
        NSLog(@"document Finished Creating");
        [self.document saveToURL:self.document.fileURL forSaveOperation:UIDocumentSaveForCreating completionHandler:OnDocumentDidLoad];
        NSLog(@"Saved to URL on disk");
} else if (self.document.documentState == UIDocumentStateClosed) {
        NSLog(@"document is closed and its needs to be opened");
        [self.document openWithCompletionHandler:OnDocumentDidLoad];
} else if (self.document.documentState == UIDocumentStateNormal) {
        NSLog(@"test document is in normal state");
        OnDocumentDidLoad(YES);
}

从第一次运行结果当数据库不存在时

 2013-08-12 14:51:35.458 <My APP>[368:11603] document doesnot exist and hence its created Start
2013-08-12 14:51:38.716 <My APP>[368:11603] document doesnot exist and hence its Finished Creating
2013-08-12 14:51:38.718 <My APP>[368:11603] NSManagedContext did save.
2013-08-12 14:51:38.718 <My APP>[368:11603] Saved to URL on disk
2013-08-12 14:51:38.721 <My APP>[368:11603] document is closed and its needs to be opened
2013-08-12 14:51:38.772 <My APP>[368:11603] NSManagedObjects did change

从第二次运行结果：当数据库存在于URL

时

2013-08-12 14:53:43.758 <MY APP> [380:11603] document is closed and its needs to be opened
2013-08-12 14:53:43.761 <MY APP>[380:11603] document is closed and its needs to be opened
2013-08-12 14:53:43.762

我理解它失败的原因，因为它不应该连续开启。我在所有视图控制器中都有相同的代码，它们控制选项卡以获取UIManagedDocument的实例。请让我知道我错过了什么。谢谢

 -(id) initWithCoder:(NSCoder *)aDecoder {

          self = [super initWithCoder:aDecoder];
          if (!self.databaseDocument) {
              [[LTDatabaseDocumentHandler sharedDatabaseDocumentHandler] performWithDocument:^    (UIManagedDocument *document) {
              self.databaseDocument = document;
        [self populateTableViewArrayFromDocument:self.databaseDocument];
         }];
   }
   return self;
 }

Answer 1

我想。我需要使用 - （void）viewWillAppear：动画方法来实例化UIManagedDocument的共享实例而不是 - （id）initWithCoder。因为只有当用户尝试查看选项卡时才会执行viewWillAppear方法。

Answer 2

我不明白这对你有什么帮助，但至少你明白了。它似乎就像viewWillAppear：可能不是初始化这类东西的最佳位置。

尝试打开现有数据库时，UITabViewController中使用的UIManagedDocument崩溃

2 个答案: