当排序的属性不完全相同时，NSFetchedResultsController无法执行 [英] NSFetchedResultsController can't performFetch when sorted attributes aren't all the same

问题描述

我有一个奇怪的问题， NSFetchedResultsController 只能处理 performFetch 所有 entity.number s是相同的数字（此 NSFetchedResultsController 使用 number 对实体进行排序。这有点像播放列表，它使用 indexNumber 属性来保持播放列表顺序。

I have a strange issue with an NSFetchedResultsController that can only handle performFetch when all the entity.numbers are the same number (this NSFetchedResultsController sorts the entities using number. This is kind of like a playlist that uses an indexNumber attribute to keep the playlist order.

- (IBAction)addSetPressed {
    int theNumber = [self.nameTextField.text intValue];
    WSet *set = [WSet wSetWithNumber:theNumber inManagedObjectContext:self.workout.managedObjectContext];
    [self.workout addExercisesObject:set];
}

self.nameTextField 在我的 UITableView 的标题中。我会在那里放一个数字，比如 1 例如，然后我按 UIButton 调用 addSetPressed 。这段代码是指将实体添加到我的模型和 NSFetchedResultsContro ller 检测模型中的更改并更新我的 UITableView 。

self.nameTextField is in my UITableView's Header. I'll put a number there, like 1 for example, and then I press a UIButton that calls addSetPressed. This code is meant to add an entity to my model and the NSFetchedResultsController detects the change in the model and updates my UITableView.

这是问题：
当我在 self.nameTextField 中输入 1 （或任何数字）时，我可以按 UIButton 我想要多次，代码效果很好。但当我更改 self.nameTextField 中的数字时，我收到一个错误：

Here's the issue: When I enter 1 (or any number) in self.nameTextField, I can press the UIButton as many times as I want to and the code works great. But when I change the number in self.nameTextField I get an error:

[__NSCFNumber localizedCaseInsensitiveCompare:]: unrecognized selector sent to instance 0xb665b80
CoreData: error: Serious application error.  Exception was caught during Core Data change processing.  This is usually a bug within an observer of NSManagedObjectContextObjectsDidChangeNotification.

我花了最近12个小时搞乱我的代码并研究问题，但我可以'弄明白。

I have spent the last 12 hours messing around with my code and researching the issue, but I can't figure it out.

如果你和我一起提示，或者可以指出一些可以提供帮助的文献，我会很棒。

It will be great if you a and tip for me, or can point me towards some literature that can help.

推荐答案

已修复！

这是问题所在。当我设置 sortDescriptor 时，我需要选择适当的选择器来比较我正在排序的属性类型。

Here's the problem. When I setup my sortDescriptor, I need to select the appropriate selector to compare the type of attribute I'm sorting by.

这是正确的，因为号码被处理为 NSNumber

This is correct since number is handled as an NSNumber

request.sortDescriptors = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:@"number" ascending:YES selector:@selector(compare:)]];

之前我有 NSString 的选择器。

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