objective-c - 在 Objective-C 中使用类别覆盖方法

Question

我可以使用类类别来覆盖已经使用类别实现的方法吗？像这样:

1) 原始方法

-(BOOL) method {
  return true;
}

2) 重写方法

-(BOOL) method {
  NSLog(@"error?"); 
  return true; 
}

这行得通，还是违法？

Answer 1

来自 Apple documentation :

Although the Objective-C language currently allows you to use a category to override methods the class inherits, or even methods declared in the class interface, you are strongly discouraged from doing so. A category is not a substitute for a subclass. There are several significant shortcomings to using a category to override methods:

• When a category overrides an inherited method, the method in the category can, as usual, invoke the inherited implementation via a message to super. However, if a category overrides a method that exists in the category's class, there is no way to invoke the original implementation.

• A category cannot reliably override methods declared in another category of the same class.

  This issue is of particular significance because many of the Cocoa classes are implemented using categories. A framework-defined method you try to override may itself have been implemented in a category, and so which implementation takes precedence is not defined.

• The very presence of some category methods may cause behavior changes across all frameworks. For example, if you override the windowWillClose: delegate method in a category on NSObject, all window delegates in your program then respond using the category method; the behavior of all your instances of NSWindow may change. Categories you add on a framework class may cause mysterious changes in behavior and lead to crashes.