关联计数更改时强制NSFetchedResultsController更新 [英] Force NSFetchedResultsController update when association count changes

问题描述

我有一个NSFetchedResultsController，它在表视图中显示项目列表，包括相关实体的计数.当为该关联添加一个对象(使用addXXXObject)时，不会调用任何回调来将更新通知我的控制器.

I have an NSFetchedResultsController which displays a list of items in a table view, including a count of an associated entity. When an object is added for this association (using addXXXObject), no callbacks are called to notify my controller of the update.

如何接收到对象添加到父实体的NSSet的通知，或者以其他方式强制获取的结果控制器进行更新?

How can I receive a notification of an object being added to the parent entity's NSSet, or otherwise force the fetched results controller to update?

要清楚，我当前正在使用parent.children.count检索计数，该计数可能不是最优的.有没有更好的方法来解决这整个问题?基本上，它只是一个类似于iPhone Mail应用程序的屏幕，其中的文件夹显示了其中的邮件数量.

To be clear, I'm currently retrieving the count using parent.children.count, which may be suboptimal. Is there a better way to go about this whole thing? It's basically just a screen like the iPhone Mail app, with folders showing a count of messages inside.

推荐答案

我的模型有些不同，但是可以轻松转换为您的模型.
我有一个树状结构:

My model is a little different, but it can easily be translated to your one.
I got a tree-like structure:

• 元素
  • 标题
  • 父母(一对一)
  • 孩子(多对多)

  添加或删除文件时，只有队列中的第一个文件夹会收到有关此更改的通知.当文件标题更改时，不会通知单个文件夹.那么，该怎么办?
  我尝试在Element类中覆盖-willChangeValueForKey:和-didChangeValueForKey:

  When a file gets added or deleted, only the first folder in the queue up gets notified about this change. When a file's title changes, not a single folder would get notified. So, what to do?
  I tried overriding -willChangeValueForKey: and -didChangeValueForKey: in my Element class.

  - (void)willChangeValueForKey:(NSString *)key
  {
      [super willChangeValueForKey:key];
      [self.parent willChangeValueForKey:@"children"];
  }
  
  - (void)didChangeValueForKey:(NSString *)key
  {
      [super didChangeValueForKey:key];
      [self.parent didChangeValueForKey:@"children"];
  }
  

  基本上，由于子文件夹之一已更改，因此该操作强制父文件夹进行更新.
  希望它也对您有用.

  Basically, what this does is forcing the parent folder to update because one of its children changed.
  Hope it works for you, too.

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