多对多关系中的 KVO 对象属性

发布于 2024-12-19 02:26:17 字数 392 浏览 3 评论 0原文

我有一个核心数据对多关系，其中包含 Parent <--->>孩子。我想设置一个键值观察机制，以便当任何子对象上的属性（例如，firstName、lastName）更改时，它会触发通知。当使用标准 KVO 语法时：

[self.parentObject addObserver:self forKeyPath:@"children" options:NSKeyValueObservingOptionNew context:NULL]

这仅在关系本身被修改时发出通知（即，在关系中添加或删除子对象），而不是在这些子对象之一的属性发生更改时发出通知。显然这就是它的设计运行方式，所以发生这种情况没有任何问题，但是我怎样才能使用 KVO 来实现我想要的要求呢？

提前致谢！

原文

I have a Core Data to-many relationship consisting of Parent <--->> Child. I would like to setup a key-value observing mechanism such that when a property (e.g. firstName, lastName) on any of the Child objects changes it triggers a notification. When using the standard KVO syntax:

[self.parentObject addObserver:self forKeyPath:@"children" options:NSKeyValueObservingOptionNew context:NULL]

this only notifies when the relationship itself is modified (i.e. a Child object is added or removed from the relationship), rather than when a property of one of those Child objects changes. Obviously this is how it was designed to operate, so there's nothing wrong with that happening, but how can I instead use KVO to achieve my desired requirement?

Thanks in advance!

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ˉ厌 2024-12-26 02:26:17

AFAIK 没有内置方法可以用一行代码观察集合对象属性。相反，当对象从集合中插入/删除时，您必须添加/删除观察者。

可以在此处找到说明和示例项目： https://web.archive.org/web/20120319115245/http://homepage.mac.com/mmalc/CocoaExamples/controllers.html
（请参阅“观察集合与观察集合中对象的属性不同”部分）

更新：
链接损坏了 - 我将其更改为 archive.org 快照。

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请持续率性 2024-12-26 02:26:17

答案有点晚了，但也许对用谷歌搜索这个的人有用。

您可以使用谓词 @"parent == %@", child 为实体子级设置一个 NSFetchedResultsController，然后将您的控制器作为委托添加到该 fetchedResultController。当子项的任何属性发生更改以及添加它们时等时，将调用委托。
下面是示例代码。我还添加了一个排序描述符，用于按子级的名称对子级进行排序，

...
NSFetchRequest* fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Child"];
fetchRequest.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES]];

NSPredicate* predicate = [NSPredicate predicateWithFormat:@"parent = %@", parent];
self.fetchResultsController.fetchRequest.predicate = predicate;

self.fetchResultsController = [[NSFetchedResultsController alloc] 
     initWithFetchRequest:fetchRequest managedObjectContext:context 
     sectionNameKeyPath:nil cacheName:nil];

self.fetchResultsController.delegate = self;
...

然后您实现委托方法

- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject
   atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type
  newIndexPath:(NSIndexPath *)newIndexPath {

以及实现所需的任何其他委托方法（文档对此有一个非常好的代码片段）

A bit of a late answer, but maybe it will be useful to someone who googles this.

You can setup an NSFetchedResultsController for the entity child with the predicate @"parent == %@", childand then add your controller as a delegate to that fetchedResultController. The delegate will be called when any of the properties of the child changes, as well as when they are added etc.
An example code follows. I have also added a sort descriptor to sort the children by their name to the

...
NSFetchRequest* fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Child"];
fetchRequest.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES]];

NSPredicate* predicate = [NSPredicate predicateWithFormat:@"parent = %@", parent];
self.fetchResultsController.fetchRequest.predicate = predicate;

self.fetchResultsController = [[NSFetchedResultsController alloc] 
     initWithFetchRequest:fetchRequest managedObjectContext:context 
     sectionNameKeyPath:nil cacheName:nil];

self.fetchResultsController.delegate = self;
...

Then you implement the delegate method

- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject
   atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type
  newIndexPath:(NSIndexPath *)newIndexPath {

And any other delegate method you need for your implementation (the documentation has a very good code snippet for this

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