如何向Cocoa中的现有协议添加方法？ [英] How to add a method to an existing protocol in Cocoa?

问题描述

我想在现有协议中扩展或添加其他方法。虽然协议特别不重要，这是我想要做的。

  @protocol NSMatrixDelegate 
  - （void）myNewMethod：（id）sender; 
 @end 
  

编译器警告我有一个相同协议的重复声明。

感谢。

解决方案

无法定义协议的类别。有两种方法：

• 使用新的正式协议


• 使用非正式协议运行时检查

正式协议

定义一个新的正式协议this：

  @protocol MyCustomMatrixDelegate< NSMatrixDelegate> 
 
  - （void）myNewMethod：（id）sender; 
 
 @end 
  

然后你会使你的自定义类符合< MyCustomMatrixDelegate> 而不是< NSMatrixDelegate> 。如果你使用这种方法，有一些需要注意的事情： [self delegate] 可能会被声明为 id< NSMatrixDelegate> 。这意味着你不能做 [[self delegate] myNewMethod：obj] ，因为< NSMatrixDelegate> 不会声明 myNewMethod：方法。

方法是重新输入 对象。可能类似：

   - （id< MyCustomMatrixDelegate>）customDelegate {
 return（id< MyCustomMatrixDelegate>）[self代表]; 
} 
  

（但是，您可能需要先进行一些类型检查， / p>

  if（[[self delegate] conformsToProtocol：@protocol（MyCustomMatrixDelegate）]）{
 return（id< MyCustomMatrixDelegate& ）[self delegate]; 
} 
 return nil; 
  

p>

然后你会：

  [[self customDelegate] myNewMethod ：obj]; 
  

非正式协议

NSObject（MyCustomMatrixDelegate）的：

$ b

  ）
 
  - （void）myNewMethod：（id）sender; 
 
 @end 
  

那么你只是不实现该方法。在您发送方法的类中，您将执行：

  if（[[self delegate] responsesToSelector：@selector myNewMethod :)]）{
 [[self delegate] myNewMethod：someSenderValue]; 
} 
  

I want to extend or add another method to an existing protocol. Although the protocol in particular is not important, this is what I am trying to do.

@protocol NSMatrixDelegate
- (void)myNewMethod:(id)sender;
@end

The compiler warns that I have a duplicate declaration of the same protocol. How would I do this properly?

Thanks.

解决方案

You can't define categories for protocols. There are 2 ways around this:

• use a new formal protocol
• use an informal protocol and runtime checking

Formal Protocol

Defining a new formal protocol would look like this:

@protocol MyCustomMatrixDelegate <NSMatrixDelegate>

- (void) myNewMethod:(id)sender;

@end

Then you would make your custom class conform to <MyCustomMatrixDelegate> instead of <NSMatrixDelegate>. If you use this approach, there's something to be aware of: [self delegate] will likely be declared as id<NSMatrixDelegate>. This means that you can't do [[self delegate] myNewMethod:obj], because <NSMatrixDelegate> does not declare the myNewMethod: method.

The way around this is to retype the delegate object via casting. Maybe something like:

- (id<MyCustomMatrixDelegate>) customDelegate {
  return (id<MyCustomMatrixDelegate>)[self delegate];
}

(However, you might want to do some type checking first, like:

if ([[self delegate] conformsToProtocol:@protocol(MyCustomMatrixDelegate)]) {
  return (id<MyCustomMatrixDelegate>)[self delegate];
}
return nil;

)

And then you'd do:

[[self customDelegate] myNewMethod:obj];

Informal Protocol

This is really a fancy name for a category on NSObject:

@interface NSObject (MyCustomMatrixDelegate)

- (void) myNewMethod:(id)sender;

@end

Then you just don't implement the method. In your class that would send the method, you'd do:

if ([[self delegate] respondsToSelector:@selector(myNewMethod:)]) {
  [[self delegate] myNewMethod:someSenderValue];
}

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