为单个KVC更改接收2个KVO通知 [英] Receiving 2 KVO notifications for a single KVC change

问题描述

我使用KVC / KVO为大学项目创建自定义绑定实现（需要自定义，因为我想做的事情超出了绑定可以做，包括在iOS上运行）。

我有一个绑定控制器注册一个对象上的许多键（使用addObserver：forKeyPath：options：context :)的KVO通知，我会收到通知。但是，我收到每个更改的两个通知。我有一个想法的解决方法，但我宁愿工作，为什么这发生和纠正它！

有没有任何想法为什么这可能发生？我确定我只有一次注册每个通知，一次注销一次会导致两个通知都停止。

感谢。

编辑：

我有一些代码的请求，所以我会把一些。目前有点粗糙，

这是我观察的属性之一（我知道这有点奇怪，但这个类本质上暴露了NSManagedObject的某些属性作为其自身的属性）：

   - （void）setName：（NSString *）name 
 {
 [self willChangeValueForKey：@name]; 
 [contact setFirstName：name]; 
 [self didChangeValueForKey：@name]; 
} 
  

这是我用来观察属性的代码，并且只在一个地方）：

  [viewModel addObserver：self 
 forKeyPath：@name
 options：（NSKeyValueObservingOptionNew | NSKeyValueObservingOptionInitial）
 context：viewController]; 
  

更改该属性后的任何调用，例如：

  viewModel.name = @Joe; 
 [viewModel setName：@Joe]; 
 [viewModel setValue：@JoeforKey：@name]; 
  

会导致以下方法：

   - （void）observeValueForKeyPath：（NSString *）keyPath ofObject：（id）object change：（NSDictionary *）change context：（void *）context 
  
解决方案
 
 
 
每次调用两次， div> 
您正在这样做：
   - （void）setName：（NSString *）name 
 {
 [self willChangeValueForKey：@name]; 
 [contact setFirstName：name]; 
 [self didChangeValueForKey：@name]; 
} 
  
但是（从它的声音） c> NSManagedObject 子类。这意味着Cocoa将尝试自动为您发送KVO通知。你也是通过发送自己的补充。解决方案：
 
 
 
 
 
覆盖 + automaticallyNotifiesObserversForKey：以返回 NO  
 
 
 
将您的方法更改为：
 
 
 
   - ）setName：（NSString *）name 
 {
 [contact setFirstName：name]; 
}  
 
 
 
 
I'm using KVC/KVO to create a custom bindings implementation for a University project (it needs to be custom as I want to do things beyond what bindings can do, including running on iOS).

I have a 'bindings controller' that registers for KVO notifications on a number of keys on an object (using addObserver:forKeyPath:options:context:) and I do receive notifications. However I am receiving two notifications for each change. I have an idea for a workaround, but I would rather work out why this is happening and correct it!

Does anyone have any ideas why this might be happening? I'm certain I have only registered each notification a single time, and deregistering a single time causes both of the notifications to stop.

Thanks.

Edit:

I have a request for some code, so I'll put some in. It's a bit rough at the moment, it's essentially still a proof of concept, so bear with me.

This is one of the properties I am observing (I know it's a bit strange, but this class essentially exposes certain properties of an NSManagedObject as properties of itself):
- (void)setName:(NSString *)name
{
    [self willChangeValueForKey:@"name"];
    [contact setFirstName:name];
    [self didChangeValueForKey:@"name"];
}
This is the code I use to observe that property (confirmed to only run once, and only in a single place):
[viewModel addObserver:self
            forKeyPath:@"name"
               options:(NSKeyValueObservingOptionNew | NSKeyValueObservingOptionInitial)
               context:viewController];
Any calls after that which change that property, e.g.:
viewModel.name = @"Joe";
[viewModel setName: @"Joe"];
[viewModel setValue: @"Joe" forKey: @"name"];
will cause the method:
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
to be called twice, with the same arguments each time.
解决方案
You're doing this:
- (void)setName:(NSString *)name
{
    [self willChangeValueForKey:@"name"];
    [contact setFirstName:name];
    [self didChangeValueForKey:@"name"];
}
But (by the sounds of it) from a non-NSManagedObject subclass. This means that Cocoa will be attempting to send KVO notifications automatically for you. You're supplementing that by sending your own too. Solutions:


Override +automaticallyNotifiesObserversForKey: to return NO
Change your method to:

- (void)setName:(NSString *)name
{
    [contact setFirstName:name];
}


                        
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