iphone – 在Objective-C中的正式和非正式协议有什么区别？

概述Objective-C中的正式和非正式协议有什么区别？ 从 Official Documentation Formal and Informal Protocols There are two varieties of protocol, formal and informal: An informal protocol is a category on NSObject, which impli Objective-C中的正式和非正式协议有什么区别？解决方法 从 Official Documentation

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.

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