如何声明和使用NSString全局常量

本文介绍了如何声明和使用NSString全局常量的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

我将一些应用程序设置存储在NSUserDefaults中. NSStrings用作键.问题是我需要使用这些NSString键在整个应用程序中访问这些设置.在应用程序的某些部分访问时，我可能会打错此类字符串键.

I store some app settings in NSUserDefaults. NSStrings are used as keys. The problem is I need to access these settings throughout the app using those NSString keys. There is a chance that I mistype such string key when accessing in some part of the app.

在整个应用程序中，我都有这样的声明

Throughout the app, I have such statements

[[NSUserDefaults standardUserDefaults] setBool:YES forKey:@"ReminderSwitch"];

BOOL shouldRemind = [[NSUserDefaults standardUserDefaults] boolForKey:@"ReminderSwitch"];

如何以及在哪里可以声明可以在整个应用程序中访问的全局NSString常量.这样，我就可以使用该常量，而不必担心会弄乱那些字符串键了.

How and where can I declare a global NSString constant which I can access throughout the app. I will then be able to use that constant without worrying about mistyping those string keys.

推荐答案

首先，您应该使用真正的extern C符号-而不是宏.这样做是这样的:

First, you should go for a real extern C symbol -- not a macro. this is done like so:

SomeFile.h

extern NSString *const MONConstantString;

SomeFile.m

NSString *const MONConstantString = @"MONConstantString";

请注意，如果混合使用ObjC和ObjC ++，则需要为C ++ TU指定extern "C"，这就是为什么您会看到#define d导出随语言而变化的原因.

note that if you use a mix of ObjC and ObjC++, you will need to specify extern "C" for C++ TUs -- that's why you will see a #defined export which varies by language.

然后，您需要将常量放在与其相关的接口附近.以您的示例为线索，您可能需要针对应用程序首选项的一组接口或声明.在这种情况下，您可以将声明添加到MONAppsPreferences标头中:

Then, you will want to put the constant near the interfaces it relates to. Taking your example as a lead, you might want a set of interfaces or declarations for your app's preferences. In that case, you might add the declaration to MONAppsPreferences header:

MONAppsPreferences.h

extern NSString *const MONApps_Pref_ReminderSwitch;

MONAppsPreferences.m

NSString *const MONApps_Pref_ReminderSwitch = @"MONApps_Pref_ReminderSwitch";

使用中:

In use:

#import "MONAppsPreferences.h"
...
[[NSUserDefaults standardUserDefaults] setBool:YES forKey:MONApps_Pref_ReminderSwitch];

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