blocks|key|2956782|text|让我进一步减少样本，并标记这些行：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2956783|VC1.h|offset|length|style|BOLD|2956784|#import+"VC2.h"++//+A

@class+VC1;

@protocol+VC1Delegate+//+B
@end

@interface+VC1+:+UIViewController+<VC2Delegate>+//+C
@end|code-block|syntax|javascript|2956785|VC2.h|2956786|#import+"VC1.h"++//+D

@class+VC2;

@protocol+VC2Delegate+//+E
@end

@interface+VC2+:+UIViewController+<VC1Delegate>+//+F
@end|2956787|考虑一下当某件东西导入VC1.h时会发生什么:它到达A行，然后导入被处理。行D不执行任何操作，因为已经导入了VC1.h。然后处理E行。然后是F行，我们得到一个错误，因为我们还没有到达B行，所以协议没有声明！|2956788|然后考虑一下，当某件东西导入VC2.h时会发生什么:它到达D行，然后导入被处理。线路A不执行任何操作，因为已经导入了VC2.h。然后处理行B。然后是C行，我们得到一个错误，因为我们还没有到达E行，所以协议没有声明！|2956789|第一步是重新考虑这两个类是否真的需要成为对方的代理。如果你能打破这个循环，那可能就是你要走的路。如果不是，您将需要重新构造您的头。最直接的方法可能是将委托放入它们自己的头中：|2956790|VC1Delegate.h|2956791|@class+VC1;

@protocol+VC1Delegate+//+B
@end|2956792|2956793|#import+"VC1Delegate.h"
#import+"VC2Delegate.h"

@interface+VC1+:+UIViewController+<VC2Delegate>+//+C
@end|2956794|VC2Delegate.h|2956795|@class+VC2;

@protocol+VC2Delegate+//+E
@end|2956796|2956797|#import+"VC1Delegate.h"
#import+"VC2Delegate.h"

@interface+VC2+:+UIViewController+<VC1Delegate>+//+F
@end|2956798|如果您现在跟踪导入，您将看到在@interface行尝试使用它们之前，将始终声明适当的协议。|2956799|entityMap^0|0|0|5|0|0|0|5|0|0|0|0|0|0|D|0|0|0|5|0|0|0|D|0|0|0|5|0|0|0^^$0|@$1|2|3|4|5|6|7|1E|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1F|8|@$D|1G|E|1H|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|1I|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|1J|8|@$D|1K|E|1L|F|G]]|9|@]|A|$]]|$1|O|3|P|5|J|7|1M|8|@]|9|@]|A|$K|L]]|$1|Q|3|R|5|6|7|1N|8|@]|9|@]|A|$]]|$1|S|3|T|5|6|7|1O|8|@]|9|@]|A|$]]|$1|U|3|V|5|6|7|1P|8|@]|9|@]|A|$]]|$1|W|3|X|5|6|7|1Q|8|@$D|1R|E|1S|F|G]]|9|@]|A|$]]|$1|Y|3|Z|5|J|7|1T|8|@]|9|@]|A|$K|L]]|$1|10|3|C|5|6|7|1U|8|@$D|1V|E|1W|F|G]]|9|@]|A|$]]|$1|11|3|12|5|J|7|1X|8|@]|9|@]|A|$K|L]]|$1|13|3|14|5|6|7|1Y|8|@$D|1Z|E|20|F|G]]|9|@]|A|$]]|$1|15|3|16|5|J|7|21|8|@]|9|@]|A|$K|L]]|$1|17|3|N|5|6|7|22|8|@$D|23|E|24|F|G]]|9|@]|A|$]]|$1|18|3|19|5|J|7|25|8|@]|9|@]|A|$K|L]]|$1|1A|3|1B|5|6|7|26|8|@]|9|@]|A|$]]|$1|1C|3|-4|5|6|7|27|8|@]|9|@]|A|$]]]|1D|$]]

Let me reduce the sample even further, and label the lines:

VC1.h

<pre><code>#import "VC2.h" // A

@class VC1;

@protocol VC1Delegate // B
@end

@interface VC1 : UIViewController &lt;VC2Delegate&gt; // C
@end
</code></pre>

VC2.h

<pre><code>#import "VC1.h" // D

@class VC2;

@protocol VC2Delegate // E
@end

@interface VC2 : UIViewController &lt;VC1Delegate&gt; // F
@end
</code></pre>

Consider what happens when something #imports VC1.h: It reaches line A, then the import is processed. Line D does nothing because VC1.h was already imported. Then line E is processed. Then line F, and we get an error because we haven't gotten to line B yet so the protocol is not declared!

Consider then what happens when something #imports VC2.h: It reaches line D, then the import is processed. Line A does nothing because VC2.h was already imported. Then line B is processed. Then line C, and we get an error because we haven't gotten to line E yet so the protocol is not declared!

The first step is to reconsider whether both of these classes really need to be each other's delegates. If you can break the cycle, that would probably be the way to go. If not, you'll need to restructure your headers. The most straightforward way is probably to put the delegates into their own headers:

VC1Delegate.h

<pre><code>@class VC1;

@protocol VC1Delegate // B
@end
</code></pre>

VC1.h

<pre><code>#import "VC1Delegate.h"
#import "VC2Delegate.h"

@interface VC1 : UIViewController &lt;VC2Delegate&gt; // C
@end
</code></pre>

VC2Delegate.h

<pre><code>@class VC2;

@protocol VC2Delegate // E
@end
</code></pre>

VC2.h

<pre><code>#import "VC1Delegate.h"
#import "VC2Delegate.h"

@interface VC2 : UIViewController &lt;VC1Delegate&gt; // F
@end
</code></pre>

If you trace through the imports now, you'll see that the appropriate protocols will now always be declared before the @interface lines try to use them.

blocks|key|265484|text|我遇到了几乎相同的问题，多亏了上面的答案，我解决了它，但方式略有不同。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|265485|我所做的就是将#行放在头文件中的协议声明之后。希望我能帮上忙。如果有人因为某些原因知道这是糟糕的编程，请让我知道|offset|length|style|BOLD|265486|entityMap^0|0|9|1B|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@$D|L|E|M|F|G]]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

I had almost the same problem, and I fixed it thanks to the answer above, but in a slightly different way.

all I did was to put the #import line after the protocol declaration in the header file.
hope I can help. and if anyone know that this is bad programing for some reason, pls let me know

blocks|key|3170863|text|在#import行上编写协议声明代码，例如|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3170864|@协议|3170865|@end|3170866|导入|3170867|@interface类名称|3170868|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|N|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|O|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|P|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|K|$]]

Write protocol declaration code above the #import lines
e.g.
<h2>@protocol -----</h2>
@end
<h1>import ----</h1>
@interface classname ---

blocks|key|263924|text|我遵循了在导入之前移动协议的修复，它修复了问题……导入包括委托，所以这是导致问题的原因。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|263925|但后来我想，我为什么要导入委托呢？我没有引用它的属性，也没有直接调用它的任何方法(这就是协议声明的用途)。|263926|我尝试注释掉委托的导入，并发现错误出现在哪里，并且发现当我导入委托时，我导入的实际上是委托正在导入的声明，即我导入A(也是我的委托)，A导入B，我实际使用的是B。因此，我将A的导入注释掉，并为B添加了导入。然后，我可以将导入协议的顺序恢复到原来的方式。|263927|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

I followed the fix of moving the protocol before the import and it fixed the problem... the import included the delegate, so that was causing the problem.

But then I thought, why was I importing the delegate anyway? I wasn't referencing its properties and I wasn't calling any of its methods directly (that's what the protocol declare was for).

I tried commenting out the import of the delegate and saw where the error came up and found that what I was importing when I was importing the delegate was actually a declaration that the delegate was importing i.e. I was importing A (also my delegate), A was importing B, what I was actually using was B. So I left the import of A commented out and added an import for B. Then I could put the import-protocol order back the way it was.

blocks|key|2957002|text|我为这个问题找到了另一个解决方案，因为我真的不喜欢在类和协议声明之间只有一些#imports的想法。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2957003|基本上，您只需将<YourProtocolName>从.h类文件移到.m文件中的类扩展|offset|length|style|CODE|2957004|因此，在.m文件中添加了|2957005|@interface+YourClassName+()+<YourProtocolName>
@end|code-block|syntax|javascript|2957006|我不知道这是否真的是一个很好的实践，但它看起来是一个避免导入周期的更干净的解决方案。|2957007|entityMap^0|0|8|I|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@$D|U|E|V|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|W|8|@]|9|@]|A|$]]|$1|J|3|K|5|L|7|X|8|@]|9|@]|A|$M|N]]|$1|O|3|P|5|6|7|Y|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

I found another solution to this issue because I didn't really like the idea of just having some #imports in between the class and the protocol declaration. 

Basically you just move <code>&lt;YourProtocolName&gt;</code> from the .h class file to the class extension in the .m file

So in your .m file you add

<pre><code>@interface YourClassName () &lt;YourProtocolName&gt;
@end
</code></pre>

I don't know if this is really a good practise but it looks like a cleaner solution to avoid the import cycles.

blocks|key|2957009|text|尝试将<+BaseViewControllerDelegate+>或<+BigViewControllerDelegate+>放在实现文件中，而不是头文件中。看起来不错。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2957010|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Try putting the &lt; BaseViewControllerDelegate > or &lt; BigViewControllerDelegate > in implementation file rather then header file. It will work.

I have two <code>view controllers A</code> and <code>B</code>, and they both have each other as their delegates.

When I did nothing except define the protocols at the beginning of the header files and <code>#import</code> the other's header file, I got two errors along the lines of -

<blockquote>
 cannot find protocol declaration for "BDelegate", which was showing in
 A.h (where I wrote ) cannot find protocol declaration for
 "ADelegate", which was showing in B.h (where I wrote )
</blockquote>

Looking online, people had written earlier that the circular inclusion of header files could be leading to the problems. They recommended either using <code>#include</code> instead, or <code>@class</code> declaration like -

<pre><code>@class A
</code></pre>

instead of

<pre><code>#import A.h
</code></pre>

inside <code>#import B.h</code>

I have tried almost every combination of these imports, and <code>@classes</code>, and <code>#include</code> but still can't get rid of the warnings. Also, solutions online recommended moving the <code>#import</code> to the <code>.m</code> files but that didn't help either. Part of the reason is that the solutions online are kinda fuzzy - if you could break it down that would be great.

Any suggestions about what can be done to fix this?

<hr>

-- BigViewController.h --

<pre><code>#import "BaseViewController.h"
#include "BaseViewController.h"

@class BigViewController;

@protocol BigViewControllerDelegate
-(void) BigViewController:(BigViewController *) bigView;
@end

@interface BigViewController : UIViewController &lt;BaseViewControllerDelegate&gt;
{ 
 //delegate
 id &lt;BigViewControllerDelegate&gt; delegate;

ivars... 
}

@properties...
@end

--------------------------------------------------
</code></pre>

-- BaseViewController.h --

<pre><code>#&lt;UIKit/UIKit.h&gt;

#import "BigViewController.h"
#include "BigViewController.h"

@class BigViewController;

@protocol BaseViewControllerDelegate
- (void) setParametersWithItemChosen:(Item *) item;
@end

@interface BaseViewController : UIViewController &lt;...BigViewControllerDelegate...&gt;
{

 ivars...

 //delegate
 id &lt;BaseViewControllerDelegate&gt; delegate;
}

@properties...
@end
</code></pre>

Cannot find protocol declaration

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

文章

问答

视频

学习中心

腾讯云实验室

直播

竞赛

腾讯云代码分析专区

腾讯iOA零信任安全管理系统专区

腾讯云架构师技术同盟交流圈

腾讯云数据库专区

腾讯云顾问专区

腾讯云原生专区

腾讯混元专区

腾讯云TCE专区

腾讯云Lighthouse专区

腾讯云HAI专区

腾讯云Edgeone专区

腾讯云存储专区

腾讯云智能专区

腾讯轻联专区 

腾讯云开发专区

TAPD专区

腾讯轻量云游戏服专区

腾讯云最具价值专家

腾讯云架构师技术同盟

腾讯云创作之星

腾讯云开发者先锋

腾讯云代码助手

云原生构建

TAPD 敏捷项目管理

Cloud Studio

SDK中心

API中心

命令行工具

涵盖代码开发、场景应用、自动测试全流程，助你从零构建专属AI助手

一站式MCP教程库，解锁AI应用新玩法

我有两个view controllers A和B，它们彼此都有自己的代理。当我除了在头文件的开头定义协议和#import对方的头文件之外什么也不做时，我得到了两个关于以下内容的错误：找不到"BDelegate“的协议声明，它显示在A.h (我写的地方)找不到"ADelegate”的协议声明，它显示在B.h (我写的地方...

问找不到协议声明
EN

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问找不到协议声明EN

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问找不到协议声明
EN