iphone中Objective C中的静态字符串变量 [英] Static string variable in Objective C on iphone

问题描述

如何创建&访问iPhone中的静态字符串（目标c）？
我在A类声明静态NSString * str = @OldValue。

How to create & access static string in iPhone (objective c)? I declare static NSString *str = @"OldValue" in class A.

如果我指定B类中的一些值为 str = @NewValue。
这个值对于B类中的所有方法都是持久的。但是如果我在C类中访问它（在B中赋值后），我将它作为OldValue获取。
我错过了什么吗？我应该在其他课程中使用extern吗？

If i assign some value to this in class B as str = @"NewValue". This value persists for all methods in class B. But if I access it in class C (after assignment in B) I am getting it as OldValue. Am I missing something? Should i use extern in other classes?

谢谢&此致，
Yogini

Thanks & Regards, Yogini

推荐答案

更新：从Xcode 8开始，Objective-C 具有类属性。注意，它主要是语法糖;这些属性不是自动合成的，因此实现与以前基本没有变化。

Update: As of Xcode 8, Objective-C does have class properties. Note, it's mostly syntactic sugar; these properties are not auto-synthesized, so the implementation is basically unchanged from before.

// MyClass.h
@interface MyClass : NSObject
@property( class, copy ) NSString* str;
@end

// MyClass.m
#import "MyClass.h"

@implementation MyClass

static NSString* str;

+ (NSString*) str 
{
    return str;
}

+ (void) setStr:(NSString*)newStr 
{
    if( str != newStr ) {
        str = [newStr copy];
    }
}
@end


// Client code
MyClass.str = @"Some String";
NSLog( @"%@", MyClass.str ); // "Some String"

参见 WWDC 2016 LLVM的新功能。类属性部分从大约5分钟开始。

See WWDC 2016 What's New in LLVM. The class property part starts at around the 5 minute mark.

原始答案：

Objective-C没有类变量，这是我认为你正在寻找的。你可以用静态变量伪装它，正如你所做的那样。

Objective-C doesn't have class variables, which is what I think you're looking for. You can kinda fake it with static variables, as you're doing.

我建议将静态NSString放在你的类的实现文件中，并提供类方法访问/改变它。这样的事情：

I would recommend putting the static NSString in the implementation file of your class, and provide class methods to access/mutate it. Something like this:

// MyClass.h
@interface MyClass : NSObject {
}
+ (NSString*)str;
+ (void)setStr:(NSString*)newStr;
@end

// MyClass.m
#import "MyClass.h"

static NSString* str;

@implementation MyClass

+ (NSString*)str {
    return str;
}

+ (void)setStr:(NSString*)newStr {
    if (str != newStr) {
        [str release];
        str = [newStr copy];
    }
}
@end

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