How to add a variable to category in Objective-C? [closed]

问题

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Closed 7 years ago.

It's requied to create a category with a new variable (of type NSArray).

OriginalClass+Extension.h:

@interface OriginalClass (Extension) {
    NSArray *_array;
}

@property (nonatomic, retain) NSArray *array;

@end

But I got the error: Cannot declare variable inside @interface or @protocol.

Please help to solve the problem.

回答1:

As the other stated, you can't. Although has H2CO3 pointed out, you can use associative references. On Apple Documents:

Note that a category can’t declare additional instance variables for the class; it includes only methods. However, all instance variables within the scope of the class are also within the scope of the category. That includes all instance variables declared by the class, even ones declared @private.

If you want to go for associated object, you can use this answer. Moreover, you can use this post by Ole Begemann.

回答2:

You can't, a category can't declare additional instance variables ...

Reference : here .

回答3:

Simple: you can't add instance variables to a class using a category.

If you need to store additional data: use associated objects.

来源：https://stackoverflow.com/questions/13000693/how-to-add-a-variable-to-category-in-objective-c