一个类可以同时实现协议吗？ [英] Can a category simultaneously implement a protocol?

问题描述

如果我为一个类创建的类别添加了也满足协议规定的契约的方法，我想将该类别标记为实现协议，从而指示Obj-C预处理，

示例委托（为了清楚起见，感谢Ole！）：

  @protocol SomeDelegate< NSObject> 
  - （void）someDelegateMessage; 
 @end 
  

示例类别：

  @interface NSObject（SomeCategory）< SomeDelegate> 
  - （void）someDelegateMessage; 
 @end 
  

而且是典型的实现

  @implement NSObject（SomeCategory）
  - （void）someDelegateMessage {} 
 @end 
  

当我真的尝试这个，我得到一个警告每个NSObject方法：

警告：类别SomeCategory未完成实施

警告：找不到-description的方法定义

$ b b

...

警告：未找到-isEqual：的方法定义

警告：category'SomeCategory'没有完全实现NSObject协议

如果我移除 SomeDelegate> ，但当然NSObject不被认为是SomeDelegate

解决方案

解决方法是在没有实现的类别上声明协议，并在不同的类别中实现该方法，例如：

  @interface NSObject（SomeCategory）< SomeDelegate> 
  - （void）someDelegateMessage; 
 @end 
 
 @implementation NSObject（SomeCategory_Impl）
  - （void）someDelegateMessage {} 
 @end 
  pre> 
 
 
如果这样做， NSObject 将被视为符合< SomeDelegate > ，并且对 someDelegateMessage 的运行时检查将成功。但是， conformsToProtocol：运行时检查将失败。
 
 
 
当然，你应该提交错误请求在核心类上声明的方法不会生成警告。
 
If a category I'm creating for a class adds methods that also fulfill the contract set out by a protocol, I'd like to flag that category class as implementing the protocol, and thereby indicate to the Obj-C pre-processor that the class effectively implements the protocol as well.

Example delegate (for clarity, thanks Ole!):
@protocol SomeDelegate <NSObject>
  - (void)someDelegateMessage;
@end
Example category:
@interface NSObject (SomeCategory) <SomeDelegate>
  - (void)someDelegateMessage;    
@end
And with an otherwise typical implementation
@implement NSObject (SomeCategory)
  - (void)someDelegateMessage {}
@end
When I actually try this, I get a warning for each NSObject method: 

  
warning: incomplete implementation of category 'SomeCategory'
  
  
warning: method definition for '-description' not found
  
  
...
  
  
warning: method definition for '-isEqual:' not found
  
  
warning: category 'SomeCategory' does not fully implement the 'NSObject' protocol
Works fine if I remove <SomeDelegate> from the declaration, but of course NSObject isn't recognized as a SomeDelegate
解决方案
A workaround is to declare the protocol on a category with no implementation, and implement the method in a different category, e.g.:
@interface NSObject (SomeCategory) <SomeDelegate>
  - (void)someDelegateMessage;    
@end

@implementation NSObject (SomeCategory_Impl)
  - (void)someDelegateMessage {}
@end
If you do this, NSObject will be considered to conform to <SomeDelegate> at compile time, and runtime checks for someDelegateMessage will succeed. However, conformsToProtocol: runtime checks will fail.

Of course, you should file a bug requesting that methods declared on the core class don’t generate warnings.

                        
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