如何通过在Obj-C中串联字符串来创建常量NSString? [英] How to create constant NSString by concatenating strings in Obj-C?

问题描述

我试图通过合并其他NSString实例来实例化一个常量NSString.

这是我在实现文件中正在做的事情:

static NSString *const MY_CONST = @"TEST";
static NSString *const MY_CONCATENATE_CONST = [NSString stringWithFormat:@"STRING %@", MY_CONST];

它导致以下编译错误:Initializer元素不是常量

我想这是因为stringWithFormat不会返回常量NSString，但是由于没有其他方法可以在Obj-C中连接字符串，我该怎么办?

感谢您的帮助，

埃里克.

解决方案

我认为您需要退后一步，考虑 if 是否需要将字符串定义为const.

很显然，该字符串不是常量，因为您试图为其分配新值-这是不可能的，因为您特别指示编译器使用const关键字来确保该值未更改. /p>

如果该字符串作为属性驻留在类中，则可以将其设置为只读属性-即访问器方法，但不能使用setter方法.这样一来，您就可以在类中内部构造自己的字符串，同时避免调用者更改其值.

I'm trying to instanciate a constant NSString by concatanating other NSString instances.

Here is what I'm doing in my implementation file :

static NSString *const MY_CONST = @"TEST";
static NSString *const MY_CONCATENATE_CONST = [NSString stringWithFormat:@"STRING %@", MY_CONST];

It leads to the following compilation error : Initializer element is not constant

I suppose this is because stringWithFormat doesn't return a constant NSString, but since there is no other way to concatenate strings in Obj-C, what am I supposed to do ?

Thanks for your help,

Eric.

解决方案

I think you need to step back and think about if the string needs to be defined as a const.

Clearly the string isn't a constant since you are trying to assign a new value to it - and that is not possible since you specifically instructed the compiler to make sure the value wasn't changed by using the const keyword.

If the string resides as a property in a class you could make it a read-only property - i.e. accessor method but no setter method. You would then be able to construct your string as you wish in the class internally while keeping the callers from changing the value.

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