协议定义重复警告

问题描述

首先，我看到了此问题以及此，但我的问题不是在那儿解决.

First, I have seen this question as well as this, but my problem is not addressed there.

我在自己的头文件中定义了协议ProtocolA.然后，我有两个ClassA和ClassB类别，它们都符合该协议，因此协议头文件被导入了它们的头文件中.

I have a protocol ProtocolA defined in its own header file. Then I have two classes ClassA and ClassB which both conform to this protocol so the protocol-header is imported in their header files.

现在，它变得有点复杂了. ClassA在第三个ClassC中使用(因此被导入).此类符合第二个协议ProtocolB.该协议还具有其自己的头文件，在其中使用和导入ClassB.因此，我的ClassC(直接或间接)导入了ClassA和ClassB(都导入了ProtocolA).这给了我关于ProtocolA的以下警告:

Now it gets a bit complicated. ClassA is used (and thus imported) in a third ClassC. This class conforms to a second protocol ProtocolB. This protocol also has its own header file where it uses and imports ClassB. So my ClassC imports (either directly or indirectly) both ClassA and ClassB (which both import ProtocolA). This gives me the following warning regarding ProtocolA:

warning: duplicate protocol definition of '…' is ignored

为什么会这样?据我了解，#import宏是完全为避免我们在#include中遇到的此类问题而发明的.如何在不使用包含保护的情况下解决问题?我真的无法删除任何导入.

Why is this happening? It was my understanding that the #import macro was invented exactly for avoiding this kind of problems which we had with #include. How can I solve the issue without using an include guard? I can't really remove any of the imports.

这是说明情况的代码:

here is the code to illustrate the situation:

ProtocolA.h

@protocol ProtocolA <NSObject>
- (void)someMethod;
@end

ClassA.h

#import "ProtocolA.h"

@interface ClassA : NSObject <ProtocolA>
...
@end

ClassB.h

#import "ProtocolA.h"

@interface ClassB : NSObject <ProtocolA>
typedef enum Type {
    TypeB1,
    TypeB2
} TypeB;
...
@end

ProtocolB.h

#import "ClassB.h"

@protocol ProtocolB <NSObject>
- (TypeB)someMethod;
@end

ClassC.h

#import "ProtocolB.h"

@interface ClassC : NSObject <ProtocolB>
...
@end

ClassC.m

#import "ClassC.h"
#import "ClassA.h" // the warning appears here

@implementation ClassC
...
@end

推荐答案

不要在ProtocolB标头中导入ClassB，只需在其中使用@class ClassB;并删除#import "ClassB"

do not Import ClassB in ProtocolB header, just use @class ClassB; in it and remove #import "ClassB"

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