从其他常量构建一个常量变量列表 [英] Build a list of constants variable from other constants

问题描述

我刚读过全局常量变量 Q& A，但我发现它们对我的问题不合适。

I've just read all of objective-c global constants variables Q&A but I found them inappropriate to my problem.

我需要一个这样的变量列表：

I need a list of variable like this:

NSString *baseURL = @"http://example.org";
NSString *mediaURL = @"http://example.org/media/";
NSString *loginURL = @"http://example.org/login/";
NSString *postURL = @"http://example.org/post/";
etc.

当然，我不能使用这段代码，因为这是一个非常糟糕的做法如果我需要更改基础网址，我必须更改所有变量。
因为我需要从应用程序的每个类访问这些变量，所以我将它们声明为全局的：

Of course I can't use this code because it's a very bad approach and if I need to change the base url I must change all variables. Since I need these variables to be accessed from every class of the app I declared them as global with this approach:

// Constants.h
extern NSString *const baseURL;
extern NSString *const mediaURL;
extern NSString *const loginURL;
extern NSString *const postURL;

// Constants.m
NSString *const baseURL = @"http://example.org";
NSString *const mediaURL = [NSString stringWithFormat:"%@%@", baseURL, @"/media/"];
NSString *const loginURL = [NSString stringWithFormat:"%@%@", baseURL, @"/login/"];
NSString *const postURL = [NSString stringWithFormat:"%@%@", baseURL, @"/post/"];

但我不能这样做，因为我得到这个错误：

BUT I can't do this because I get this error:

Initializer element is not a compile-time constant

发生这种情况是因为对象在运行时工作。

This happens because objects works at runtime.

现在我的问题是，我希望一劳永逸，什么是好的在网络应用程序中处理这种相当常见的情况的好方法？

Now my question is, once and for all I hope, what is a nice and good way to handle this pretty usual scenario in network apps?

我认为使用类（或单例类）来处理常量变量有点矫枉过正，它也是过于冗长的使用类似于 [MyClass globalVar] 每次我需要它。

I think use a class (or a singleton class) for handle the constants variables is a bit overkill, and it's also too verbose use something like [MyClass globalVar] every time I need it.

关于它的想法？ / p>

Ideas about it?

推荐答案

我知道这是过时的，但我只是使用预处理器宏，并让常量字符串连接处理它。

I know it's old-fashioned but I'd just use preprocessor macros and let constant string concatenation handle it.

#define baseURL @"http://example.org"
#define mediaURL baseURL@"/media/"

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