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
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.
这篇关于Objective-C中正式和非正式协议之间的区别是什么？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！