ios - Swift:为什么从 NSManagedObject 继承会破坏我的属性？

Question

我是一个 Swift/IOS 新手，我根本无法理解 CoreData 的一些内容。

我有一个类，其中包含一些非可选属性，这些属性由指定的初始值设定项初始化。然后，如果我将该类设置为从 NSManagedObject 继承，那么我会突然收到错误

Stored property X requires an initial value or should be @NSManaged.

为什么 Swift 突然认为我的属性没有初始化，尽管它们显然已经初始化了？

此外，我读到@NSManaged“告诉编译器属性的存储和实现将由 CoreData 处理”，但这是什么意思？

任何答案将不胜感激..

Answer 1

我实际上昨天才读到这个。

Yes, it kinda really acts like @dynamic -- technically it might be identical even. Semantically there is a slight difference:

@dynamic says 'compiler, don't check if my properties are also implemented. There might be no code you can see but I guarantee it will work at runtime'

@NSManaged now says 'compiler, don't check those properties as I have Core Data to take care of the implementation - it will be there at runtime'

so you could even say: @NSManaged is syntactic sugar that is a more narrow version of dynamic :)

取自此question

Swift 的一大插入力是使语言变得极其安全，就像在本例中一样，检查属性是否在编译时实现。如果我理解正确的话，CoreData 不太符合这些编译时检查，因此添加 @NSManaged 让编译器知道变量将被处理。

来自Apple :

You use the @NSManaged attribute to inform the Swift compiler that Core Data provides the storage and implementation of a declaration at runtime.