iphone - NSFileManager fileExistsAtPath 总是在设备中返回 NO 而不是在模拟器中

Question

我按照 iOS 上的斯坦福课程 - 核心数据课程编写了一个应用程序。我的应用程序在模拟器上运行良好，但在设备上导致问题，[NSFileManager defaultManager] fileExistsAtPath:总是返回 NO，导致应用程序SAveFORcreating总是进入，一段时间后它变慢并且不再从核心数据加载数据。这在模拟器中不会发生。所以请大家帮忙！

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];

    if (!self.recipiesDatabase) {  
        NSURL *url = [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
        self.fileurl = [url URLByAppendingPathComponent:@"RecipiesDatabase"];
        NSLog(@"URL IN FILE %@", url);
        self.recipiesDatabase = [[UIManagedDocument alloc] initWithFileURL:self.fileurl]; // setter will create this for us on disk
    }
}

- (void)useDocument
{


    if (![[NSFileManager defaultManager] fileExistsAtPath:[self.recipiesDatabase.fileURL path] ]) {
        // does not exist on disk, so create it
        [self.recipiesDatabase saveToURL:self.recipiesDatabase.fileURL forSaveOperation:UIDocumentSaveForCreating completionHandler:^(BOOL success) {
            NSLog(@"No existe");
            [self setupFetchedResultsController];
            [self fetchFlickrDataIntoDocument:self.recipiesDatabase];

        }];
    } else if (self.recipiesDatabase.documentState == UIDocumentStateClosed) {
        // exists on disk, but we need to open it
        [self.recipiesDatabase openWithCompletionHandler:^(BOOL success) {
            NSLog(@"OPen");
            [self setupFetchedResultsController];
            //[self fetchFlickrDataIntoDocument:self.recipiesDatabase];

        }];
    } else if (self.recipiesDatabase.documentState == UIDocumentStateNormal) {
        // already open and ready to use
        NSLog(@"Normal");
        [self setupFetchedResultsController];

    }
}