如何在头文件（.h）中创建一个不可变的readonly属性，在implementaion（.m）中有一个可变的readwrite属性， [英] How to make an immutable readonly property in the header file (.h), a mutable readwrite property in implementaion (.m)

问题描述

我有一个对象，它包含一个字典 JSONData 。从头文件和其他访问它的类，我希望这个属性只能是只读的和不可变的。

I have an object that holds a dictionary JSONData. From the header file, and to the other classes that'll access it, I want this property to only be read-only and immutable.

@interface MyObject : NSObject

@property (readonly, strong, nonatomic) NSDictionary *JSONData;

@end

但是，我需要 readwrite 和可变参数，如下所示，但不起作用：

However, I need it to be readwrite and mutable from the implementation file, like this, but this doesn't work:

@interface MyObject ()

@property (readwrite, strong, nonatomic) NSMutableDictionary *JSONData;

@end

@implementation MyObject

// Do read/write stuff here.

@end

有什么我可以做的，我要去的抽象？我看了其他问题，虽然我已经知道如何从 .h 和<$ c中创建属性 readonly $ c> readwrite 从 .m ，我找不到任何关于可变性的差异。

Is there anything I can do to enforce the kind of abstraction I'm going for? I looked at the other questions and while I already know how to make a property readonly from .h and readwrite from .m, I can't find anything about the difference in mutability.

推荐答案

您的实现中需要一个单独的私有可变变量。您可以覆盖getter以返回不可变对象。

You need a separate private mutable variable in your implementation. You can override the getter to return an immutable object.

@interface MyObject () {
  NSMutableDictionary *_mutableJSONData;
}
@end

@implementation MyObject 

// ...

-(NSDictionary *)JSONData {
   return [NSDictionary dictionaryWithDictionary:_mutableJSONData];
}

// ...
@end

不需要实现setter，因为它是 readonly 。

No need to implement the setter, as it is readonly.

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