在@implementation而不是@interface定义的类变量? [英] Class variable defined at @implementation rather than @interface?

问题描述

我是Objective-C的新手，但我对自己在其他任何地方都没有真正解决过的问题感到好奇.

I'm new to Objective-C, but I am curious about something that I haven't really seen addressed anywhere else.

谁能告诉我在@interface块处声明的私有变量与在类方法之外的@implementation块内声明的变量之间的区别是什么?

Could anyone tell me what is the difference between a private variable that is declared at the @interface block versus a variable that is declared within the @implementation block outside of the class methods, i.e:

@interface Someclass : NSObject {

 NSString *forExample;

}

@end

vs.

@implementation Someclass

 NSString *anotherExample;

-(void)methodsAndSuch {}

@end

似乎两个变量(forExample，anotherExample)在整个类中都可以平等地访问，而我在它们的行为上并没有真正的区别.第二种形式也称为实例变量吗?

It seems both variables ( forExample, anotherExample ) are equally accessible throughout the class and I can't really find a difference in their behaviour. Is the second form also called an instance variable?

推荐答案

后者未定义实例变量.而是在.m文件中定义全局变量.这样的变量对于任何对象实例都不是唯一的或一部分.

The latter is not defining an instance variable. Rather, it is defining a global variable in the .m file. Such a variable is not unique to or part of any object instance.

此类全局变量有其用途(大致等同于C ++静态成员；例如，存储一个单例实例)，但是通常您会在@implementation指令之前在文件顶部定义它们.

Such globals have their uses (roughly equivalent C++ static members; e.g. storing a singleton instance), but normally you would define them at the top of the file before the @implementation directive.

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