详细信息在评论中。
以下代码：
// Perform the fetch...
NSError *error = nil;
if (![[self fetchedResultsController] performFetch:&error]) {
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
// Confirm that objects were fetched by counting them...
NSLog(@"Number of Objects = %i",
[[fetchedResultsController fetchedObjects] count]);
// Confirm that sections exist by counting them...
NSLog(@"Numbers of Sections = %i",
[[fetchedResultsController sections] count]);
for (id section in [fetchedResultsController sections]) {
// Count number of objects in each section
// _The fact that this outputs 0 is the first sign of trouble_
NSLog(@"Number of Objects in Section = %i", [section numberOfObjects]);
}
for (Reminder *reminder in [fetchedResultsController fetchedObjects]) {
// Confirm that the objects fetched are in fact real objects
// by accessing their "textContent" property...
NSLog(@"textContent=%@", reminder.textContent);
// Show that the fetched objects are being returned
// with a (null) indexPath...
// _The second sign of trouble..._
NSLog(@"IndexPath=%@",
[fetchedResultsController indexPathForObject:reminder]);
}
NSUInteger indexArr[] = {0,0};
NSIndexPath *indexPath = [NSIndexPath indexPathWithIndexes:indexArr
length:2];
// _Application crashes on this line because the fetched
// objects do not have indexPaths_
Reminder *testReminder = (Reminder *)[fetchedResultsController
objectAtIndexPath:indexPath];
NSLog(@"textContent = %@", testReminder.textContent);
结果如下：
2010-07-17 00:48:41.865 Reminders[27335:207] Number of Objects = 3
2010-07-17 00:48:41.867 Reminders[27335:207] Numbers of Sections = 1
2010-07-17 00:48:41.868 Reminders[27335:207] Number of Objects in Section = 0
2010-07-17 00:48:41.870 Reminders[27335:207] textContent=Imported Object 3
2010-07-17 00:48:41.871 Reminders[27335:207] IndexPath=(null)
2010-07-17 00:48:41.873 Reminders[27335:207] textContent=Imported Object 2
2010-07-17 00:48:41.873 Reminders[27335:207] IndexPath=(null)
2010-07-17 00:48:41.874 Reminders[27335:207] textContent=Imported Object 1
2010-07-17 00:48:41.875 Reminders[27335:207] IndexPath=(null)
2010-07-17 00:48:41.887 Reminders[27335:207] *** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[NSCFArray objectAtIndex:]: index (0) beyond bounds (0)'
任何想法将不胜感激。仅供参考，如果我使用不同的模板作为起点，上面的代码可以在单独的应用程序中完美运行。即如果我使用“基于窗口的应用程序”模板，代码将失败。如果我使用“基于导航的应用程序”，代码将按预期工作。
更新： TechZen 想知道问题是否是由我的提醒实体引起的。我认为这是一个好主意，所以我做了以下事情：
创建两个默认模板应用程序：一个“基于窗口的应用程序”和一个“基于导航的应用程序”（都启用了 Core Data）
将执行上述测试所需的最少代码从基于导航复制到基于窗口（几乎只是“xcdatamodel”文件、fetchedresultscontroller 和添加测试对象的方法）。
上面的代码在新的“无提醒实体”的基于窗口的应用程序中仍然失败。（在这个新的测试应用程序中，实际上我自己编写的代码为零（在测试代码之外），它只是模板代码剪切和粘贴在一起。）
所以现在，我正在寻找在创建“基于窗口的应用程序”之后运行上述代码的任何方法。这是使用基于导航的默认实体执行测试的代码，以防有人有兴趣尝试一下：
更新请注意，正如 TechZen 在下面指出的那样，无论使用空数据库运行此代码都会崩溃，因此如果从基于窗口的应用程序开始，首先向数据库添加一些对象，然后添加测试代码。
// Confirm that objects were fetched
NSLog(@"Number of Objects = %i",
[[fetchedResultsController fetchedObjects] count]);
// Confirm that sections exist
NSLog(@"Numbers of Sections = %i",
[[fetchedResultsController sections] count]);
for (id section in [fetchedResultsController sections]) {
// Count number of objects in sections
// _The fact that this outputs 0 is the first sign of trouble_
NSLog(@"Number of Objects in Section = %i", [section numberOfObjects]);
}
for (NSManagedObject *managedObject in [fetchedResultsController fetchedObjects]) {
// Confirm that the objects fetched are in fact real objects,
// by accessing their "timeStamp" property
NSLog(@"TimeStamp=%@", [[managedObject valueForKey:@"timeStamp"] description]);
// Show that the fetched objects are being returned
// with a (null) indexPath
// _The second sign of trouble..._
NSLog(@"IndexPath=%@",
[fetchedResultsController indexPathForObject:managedObject]);
}
NSUInteger indexArr[] = {0,0};
NSIndexPath *indexPath = [NSIndexPath indexPathWithIndexes:indexArr
length:2];
// _Application crashes on this line, because the fetched
// objects do not have indexPaths_
NSManagedObject *managedObject = [fetchedResultsController
objectAtIndexPath:indexPath];
NSLog(@"textContent = %@", [[managedObject valueForKey:@"timeStamp"] description]);
UPDATE这里是使用新的剪切粘贴代码时的输出
2010-07-18 15:33:41.264 Reminders[30898:207] Number of Objects = 3
2010-07-18 15:33:41.266 Reminders[30898:207] Numbers of Sections = 1
2010-07-18 15:33:41.267 Reminders[30898:207] Number of Objects in Section = 0
2010-07-18 15:33:41.270 Reminders[30898:207] TimeStamp=2010-07-18 13:59:00 -0400
2010-07-18 15:33:41.271 Reminders[30898:207] IndexPath=(null)
2010-07-18 15:33:41.272 Reminders[30898:207] TimeStamp=2010-07-18 13:59:00 -0400
2010-07-18 15:33:41.273 Reminders[30898:207] IndexPath=(null)
2010-07-18 15:33:41.274 Reminders[30898:207] TimeStamp=2010-07-18 13:58:59 -0400
2010-07-18 15:33:41.275 Reminders[30898:207] IndexPath=(null)
2010-07-18 15:33:41.276 Reminders[30898:207] *** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[NSCFArray objectAtIndex:]: index (0) beyond bounds (0)'
更新所以我将这个问题缩小为与 SDK 版本相关的问题，我现在有一个项目，如果我使用 Simulator 3.2 构建它会崩溃，而使用 Simulator 3.1.3 构建它可以正常工作。但是如果我添加一个 UITableViewController，然后使用 Simulator 3.2 构建，那么它又可以正常工作了。所以我创建了一个新的 stackoverflow帖子来问这个问题：如果你使用 NSFetchedResultsController 没有 UITableViewController，你如何与对象交互？（因为 IndexPaths 不可靠）。
更新这个问题（暂时）通过使用 -[NSFetchedResultsController fetchedObjects] objectAtIndex:]来访问对象来解决。