在 Swift 中使用 obj-c typedef [英] Using obj-c typedef in Swift

问题描述

我有一个 typedef:

I have a typedef as so:

typedef NSString VMVideoCategoryType;

extern VMVideoCategoryType *const VMVideoCategoryType_MusicVideo;
extern VMVideoCategoryType *const VMVideoCategoryType_Audio;
extern VMVideoCategoryType *const VMVideoCategoryType_Performance;
extern VMVideoCategoryType *const VMVideoCategoryType_Lyric;
extern VMVideoCategoryType *const VMVideoCategoryType_Show;

我已将此文件包含在桥接头中.但是，当我尝试在 Swift 文件中访问 VMVideoCategoryType 时出现错误:

I've included this file in the bridging header. However, when I try to access VMVideoCategoryType in a Swift file I get an error:

使用未声明的类型VMVideoCategoryType"

有什么办法可以使这项工作正常进行，还是我必须在 Swift 中完全重新定义这种类型?

Is there any way to make this work or do I have to completely re-define this type in Swift?

推荐答案

我有点猜测，不过原因好像是 Objective-C不能静态分配像 NSString 这样的对象(参见例如 Objective-C 中的对象是否曾经在堆栈上创建?).如果

I am a little bit speculating, but the reason seems to be that Objective-C objects like NSString cannot be statically allocated (see e.g. Are objects in Objective-C ever created on the stack?). If

typedef NSString VMVideoCategoryType;

被导入 Swift 然后你可以声明一个局部变量

were imported into Swift then you could declare a local variable

var foo : VMVideoCategoryType

这将是一个 NSString 而不是一个指向 NSString 的指针.

which would be a NSString and not a pointer to NSString.

还要注意，你在 Swift 中看到的 NSString 对应于 NSString *在 Objective-C 中.

Note also that what you see in Swift as NSString corresponds to NSString * in Objective-C.

如果您将 VMVideoCategoryType 定义为 NSString * 的 typedef然后它在 Swift 中可见:

If you define VMVideoCategoryType as a typedef for NSString * then it is visible in Swift:

typedef NSString * VMVideoCategoryType;

extern VMVideoCategoryType const VMVideoCategoryType_MusicVideo;
// ...

这篇关于在 Swift 中使用 obj-c typedef的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！