如何在 Swift 中使用 Objective-C #define [英] How to use a Objective-C #define from Swift

问题描述

我正在迁移一个 UIViewController 类以使用 Swift 进行一些训练.我通过桥接头成功使用了 Objective-C 代码，但我需要导入一个包含 #define 指令的常量文件.

I am migrating a UIViewController class to train a bit with Swift. I am successfully using Objective-C code via the bridging header but I have the need of importing a constants file that contains #define directives.

我在 Using Swift with Cocoa 中看到了和Objective-C(简单宏)如下:

I have seen in Using Swift with Cocoa and Objective-C (Simple macros) the following:

简单宏

在 C 和 Objective-C 中通常使用 #define 指令来定义原始常量，而在 Swift 中则使用全局常量.例如，常量定义 #define FADE_ANIMATION_DURATION 0.35 可以用 Swift 更好地表示为 let FADE_ANIMATION_DURATION = 0.35.因为简单的类常量宏直接映射到 Swift 全局变量，所以编译器会自动导入在 C 和 Objective-C 源文件中定义的简单宏.

Where you typically used the #define directive to define a primitive constant in C and Objective-C, in Swift you use a global constant instead. For example, the constant definition #define FADE_ANIMATION_DURATION 0.35 can be better expressed in Swift with let FADE_ANIMATION_DURATION = 0.35. Because simple constant-like macros map directly to Swift global variables, the compiler automatically imports simple macros defined in C and Objective-C source files.

所以，这似乎是可能的.我已将包含我的常量的文件导入到桥接头中，但我的 .swift 文件没有可见性，无法解析.

So, it seems it's possible. I have imported the file containing my constants into the bridging header, but I have no visibility from my .swift file, cannot be resolved.

我应该怎么做才能让我的常量对 Swift 可见?

What should I do to make my constants visible to Swift?

更新:

似乎可以使用 NSString 常量，但不能使用布尔值:

It seems working with NSString constants, but not with booleans:

#define kSTRING_CONSTANT @"a_string_constant" // resolved from swift
#define kBOOL_CONSTANT YES // unresolved from swift

推荐答案

目前，一些 #define 被转换，一些没有.更具体地说:

At the moment, some #defines are converted and some aren't. More specifically:

#define A 1

...变成:

var A: CInt { get }

或者:

#define B @"b"

...变成:

var B: String { get }

很遗憾，Swift 编译器无法识别和转换 YES 和 NO.

Unfortunately, YES and NO aren't recognized and converted on the fly by the Swift compiler.

我建议你将你的 #defines 转换为实际的常量，这比 #defines 好.

I suggest you convert your #defines to actual constants, which is better than #defines anyway.

.h:

extern NSString* const kSTRING_CONSTANT;
extern const BOOL kBOOL_CONSTANT;

.m

NSString* const kSTRING_CONSTANT = @"a_string_constant";
const BOOL kBOOL_CONSTANT = YES;

然后 Swift 会看到:

And then Swift will see:

var kSTRING_CONSTANT: NSString!
var kBOOL_CONSTANT: ObjCBool

另一种选择是将您的 BOOL 定义更改为

Another option would be to change your BOOL defines to

#define kBOOL_CONSTANT 1

更快.但不如实际常量.

Faster. But not as good as actual constants.

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