Objective-C 中的正式协议(protocol)和非正式协议(protocol)有什么区别？
最佳答案
Formal and Informal Protocols
There are two varieties of protocol, formal and informal:
An informal protocol is a category on NSObject, which implicitly makes almost all objects adopters of the protocol. (A category is a language feature that enables you to add methods to a class without subclassing it.) Implementation of the methods in an informal protocol is optional. Before invoking a method, the calling object checks to see whether the target object implements it. Until optional protocol methods were introduced in Objective-C 2.0, informal protocols were essential to the way Foundation and AppKit classes implemented delegation.
A formal protocol declares a list of methods that client classes are expected to implement. Formal protocols have their own declaration, adoption, and type-checking syntax. You can designate methods whose implementation is required or optional with the @required and @optional keywords. Subclasses inherit formal protocols adopted by their ancestors. A formal protocol can also adopt other protocols.
Formal protocols are an extension to the Objective-C language.
关于iphone - Objective-C 中的正式协议(protocol)和非正式协议(protocol)有什么区别？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/3082383/