Swift 类使用 Objective-C 类使用 Swift 类 [英] Swift class using Objective-C class using Swift class

问题描述

我有一个 obj-c 项目，我成功地向其中添加了一个新的 Swift 类 A，该类正被一些现有的 obj-c 类 B 使用 - 使用自动生成的MyProject-Swift.h"标头作为预期.

I have an obj-c project to which I successfully added a new Swift class A, which is being used by some existing obj-c class B - the use of the automatically generated "MyProject-Swift.h" header worked as expected.

我还成功添加了一个新的 Swift 类 C，它使用了一些现有的 obj-c 类 D - 桥接头的使用也按预期工作.

I also successfully added a new Swift class C that uses some existing obj-c class D - the use of the bridging header also worked as expected.

然而，假设我想从我的 Swift 类 C 引用现有的 obj-c 类 B(它又引用新的 Swift 类 A).为了做到这一点，我需要将B.h"导入到桥接头中.但是，如果我这样做，我会在 B 类中收到错误消息:未找到‘MyProject-Swift.h’文件"(即不再生成该文件).

However, suppose I want to refer from my Swift class C to the existing obj-c class B (which in turn refers to the new Swift class A). In order to do that I need to import "B.h" to the bridging header. However, if I do that I get an error in class B: "'MyProject-Swift.h' file not found" (i.e., the file is no longer generated).

我做错了什么还是这是 Swift 和 Objective-C 之间不允许的一种交互?好像有一种编译器无法解决的循环引用.

Am I doing something wrong or is this a kind of interaction between Swift and Objective-C that is not allowed? It looks like there is a kind of circular reference that the compiler is unable to solve.

--- 编辑---

我会尝试通过添加一些代码来使问题更清楚.

I'll try to make the question clearer by adding some code.

-- 序言 --

我向 obj-c 项目添加了一个新的 Swift 类:

I added a new Swift class to an obj-c project:

//  SwiftClassA.swift
import Foundation
@objc class SwiftClassA : NSObject {
    var myProperty = 0
}

代码正确编译并在自动生成的MyProject-Swift.h"头文件中被翻译成 obj-c 存根，如下所示:

The code compiles correctly and is translated into obj-c stubs in the automatically generated "MyProject-Swift.h" header like so:

// MyProject-Swift.h
...
SWIFT_CLASS("_TtC7MyProject11SwiftClassA")
@interface SwiftClassA : NSObject
@property (nonatomic) NSInteger myProperty;
- (instancetype)init OBJC_DESIGNATED_INITIALIZER;
@end

现在，一个 obj-c 类使用 SwiftClassA:

Now, one obj-c class uses SwiftClassA:

//  ObjCClass.h
#import <Foundation/Foundation.h>
#import <MyProject-Swift.h>
@interface ObjCClass : NSObject
@property (nonatomic, strong) SwiftClassA *aProperty;
@property (nonatomic) int *aNumber;
@end

这也可以无缝运行.

-- 问题 --

我现在可以创建一个新的 Swift 类来引用使用 Swift 类 SwiftClassA 的 obj-c 类 (ObjCClass) 吗?

Can I now create a new Swift class that refers to the obj-c class (ObjCClass) that is using the Swift class SwiftClassA?

这是我做不到的.

如果我添加新的 Swift 类:

If I add the new Swift class:

//  SwiftClassB.swift
import Foundation
@objc class SwiftClassB : NSObject {
    var aPropertyOfClassB = 1
    func someFunc() {
        var objCObject = ObjCClass()
        var theProperty = objCObject.aProperty
        print("The property is \(theProperty)")
    }
}

这当然不会编译，因为使用未解析的标识符‘ObjCClass’".所以我需要将它添加到桥接头文件中:

this of course won't compile because of "Use of unresolved identifier 'ObjCClass'". So I need to add that to the bridging header file:

//  BridgingHeader.h
#ifndef MyProject_BridgingHeader_h
#define MyProject_BridgingHeader_h
...
#import "ObjCClass.h"
#endif

但是，如果我这样做，ObjCClass.h 文件将无法编译并给出未找到‘MyProject-Swift.h’文件".

However, if I do that, the ObjCClass.h file won't compile giving a "'MyProject-Swift.h' file not found".

我在几个地方读到过(虽然没有例子)，这可能意味着存在循环引用，并且使用@class 的前向引用可以解决问题.但是，我不确定需要前向引用的内容和位置，我所有的尝试都失败了.

I've read in several places (with no example, though) that this may mean that there is a circular reference and that a forward reference using @class could solve the problem. However, I'm not sure what needs to be forward referenced and where, and all my attempts failed.

我希望这个问题现在不再令人困惑！

I hope the question is no longer confusing now!

推荐答案

这是一个典型的循环引用问题.

This is a typical cyclical referencing problem.

请仔细阅读文档:

为避免循环引用，不要将 Swift 导入 Objective-C 头文件.相反，您可以转发声明一个 Swift 类以在 Objective-C 标头中使用它.请注意，您不能在 Objective-C 中继承 Swift 类.

To avoid cyclical references, don’t import Swift into an Objective-C header file. Instead, you can forward declare a Swift class to use it in an Objective-C header. Note that you cannot subclass a Swift class in Objective-C.

所以，你应该在.h中使用forward declare"，在.m中使用#import:

So, you should use "forward declare" in .h, and #import in .m:

//  ObjCClass.h
#import <Foundation/Foundation.h>

@class SwiftClassA;

@interface ObjCClass : NSObject
@property (nonatomic, strong) SwiftClassA *aProperty;
@property (nonatomic) int *aNumber;
@end

// ObjCClass.m
#import "ObjCClass.h"
#import "MyProject-Swift.h"

@implementation ObjCClass
// your code
@end

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