Objective-C中正式和非正式协议之间的区别是什么？ [英] What's the difference between formal and informal protocols in Objective-C?

问题描述

Objective-C中正式和非正式协议之间有什么区别？

What's the difference between formal and informal protocols in Objective-C?

推荐答案

来自官方文档

正式和非正式协议

有两种协议，
正式和非正式：

There are two varieties of protocol, formal and informal:

• 非正式协议是NSObject上的一个类别，隐含地
  使几乎所有对象都采用
  协议。 （一个类别是一个
  语言特性，它使你能够在没有
  子类化的情况下向一个类添加
  。）非正式协议中
  方法的实现是
  可选的。在调用方法之前，
  调用对象检查
  目标对象是否实现了
  。在Objective-C 2.0中引入了
  的可选协议方法之前，
  非正式协议对于
  是必不可少的，就像Foundation和AppKit类
  实现委托一样。

• 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.

正式协议声明了客户类
预计要实现的方法列表。正式的
协议有自己的声明，
采用和类型检查语法。
您可以使用@required和@optional
关键字指定需要
实现的方法或可选的
。子类继承其祖先采用的正式
协议。
正式协议也可以采用其他
协议。

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.

正式协议是对
Objective-C语言。

Formal protocols are an extension to the Objective-C language.

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