为什么Core Data管理对象的+ initialize方法被调用两次？ [英] Why is the +initialize method of Core Data managed objects being called twice?

问题描述

我有一个具有 + initialize 方法的托管核心数据对象。 （如果重要的话，我想使用该方法初始化一个静态变量，这是昂贵的设置）。测试初始化​​代码时我惊讶地发现， + initialize 方法被调用两次。

I have a managed core data object with a +initialize method. (If it matters, I am looking to use that method to initialize a static variable that is expensive to to set up.) While testing that initialization code I was surprised to discover that the +initialize method is getting called twice.

第一次初始化正在调用 self 定义为（Class）MyClass ，如我所料。

The first time initialize is being called self is defined as (Class) MyClass, as I would expect.

第二次初始化正在调用 self 定义为（Class）MyClass_MyClass _ ，这导致我怀疑一些不寻常的初始化为Core Data管理对象。

The second time initialize is being called self is defined as (Class) MyClass_MyClass_, which leads me to suspect some sort of unusual initialization for Core Data managed objects.

虽然这不会对我造成问题（我可以测试看看静态变量是否已经被初始化，无论如何我会做，以处理ubclassing），它让我怀疑核心数据在做一些事情在对象或类生命周期，我不明白。有人可以向我解释在 MyClass_MyClass _ + initialize 方法调用中发生了什么吗？

While this doesn't pose a problem for me (I can just test to see if the static variable has already been initialized, which I would do anyway, to handle ubclassing), it makes me suspect that Core Data is doing something in the object or class lifecycle that I don't understand. Can someone explain to me what is going on in this MyClass_MyClass_ +initialize method invocation?

推荐答案

Core Data属性的访问器方法是在运行时动态创建的。
这通过创建子类 MyClass_MyClass _ （ MyClass ）并添加
必要的方法到子类。

The accessor methods for Core Data properties are dynamically created at runtime. This works by creating a subclass MyClass_MyClass_ (of MyClass) and adding the necessary methods to the subclass.

核心数据也有一些技巧隐藏事实
，你的实体的对象实际上是子类的实例：

Core Data also does some tricks to hide the fact that that the objects of your entity are actually instances of the subclass:

e = [NSEntityDescription insertNewObjectForEntityForName:@"MyClass" inManagedObjectContext:context];
NSLog(@"%@", [e class]);               // --> MyClass
NSLog(@"%s", object_getClassName(e));  // --> MyClass_MyClass_

如果不为您的实体设置自定义类，也许会更加明显。
在这种情况下，输出是

Perhaps it becomes even more obvious if you don't set a custom class for your entity. In that case the output is

NSLog(@"%@", [e class]);               // --> NSManagedObject
NSLog(@"%s", object_getClassName(e));  // --> NSManagedObject_MyClass_

因此 e NSManagedObject 的实例，但实际上是动态创建的子类 NSManagedObject_< EntityName> _ 的实例
。这个子类
实现所有的访问器方法（对于这个实体是唯一的）。

So e "looks like" an instance of NSManagedObject, but is indeed an instance of a dynamically created subclass NSManagedObject_<EntityName>_. This subclass implements all the accessor methods (which are unique to this entity).

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