cocoa-touch - 在索引 501 处获取的对象有一个乱序的部分名称 'JOURNAL OF APPLIED PHYSICS. Objects must be sorted by section name'

Question

我有一个包含期刊章节名称的文章数据库。一篇是《Journal of Applied Physics》，一篇是《JOURNAL OF APPLIED PHYSICS》。当我使用

[[NSSortDescriptor alloc] initWithKey:@"Journal" ascending:YES elector:@selector(caseInsensitiveCompare:)]

要获取数据，它会给我错误消息。

The fetched object at index 501 has an out of order section name 'JOURNAL OF APPLIED PHYSICS. Objects must be sorted by section name'

我已经在使用不区分大小写的比较，那么为什么这行不通呢？帮忙？

=======用于获取数据的代码=======

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];

NSEntityDescription *entity = [NSEntityDescription entityForName:@"Article" 
                                          inManagedObjectContext:SharedMOC];

[fetchRequest setEntity:entity];

NSSortDescriptor *journalSortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"Journal" 
                                                                     ascending:ascending 
                                                                      selector:@selector(caseInsensitiveCompare:)];

NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:journalSortDescriptor,  nil];

[fetchRequest setSortDescriptors:sortDescriptors];

NSFetchedResultsController *a = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest 
                                                                    managedObjectContext:SharedMOC 
                                                                      sectionNameKeyPath:[self selectedSortSection]
                                                                               cacheName:cacheName];

Answer 1

我的直觉告诉我，而不是:

[fetchRequest setSortDescriptors:[self getSortDescriptor]];

你应该写:

[fetchRequest setSortDescriptors:sortDescriptors];