协议与类别 [英] Protocol versus Category

问题描述

有人能解释Objective-C中的协议和类别之间的区别吗?您什么时候使用另一个?

Can anyone explain the differences between Protocols and Categories in Objective-C? When do you use one over the other?

推荐答案

协议与Java中的接口是一回事:本质上是一个契约，说，任何实现此协议的类也将实现这些协议.方法."

A protocol is the same thing as an interface in Java: it's essentially a contract that says, "Any class that implements this protocol will also implement these methods."

另一方面，类别仅将方法绑定到类.例如，在 Cocoa 中，我可以为NSObject创建一个类别，该类别允许我将方法添加到NSObject类(当然还有所有子类)中，即使我真的没有访问NSObject 的机会.

A category, on the other hand, just binds methods to a class. For example, in Cocoa, I can create a category for NSObject that will allow me to add methods to the NSObject class (and, of course, all subclasses), even though I don't really have access to NSObject.

总结:协议指定了类将实现的方法；类别将方法添加到现有的类中.

To summarize: a protocol specifies what methods a class will implement; a category adds methods to an existing class.

然后，应明确每种方法的正确用法:使用协议声明类必须实现的一组方法，并使用类别将方法添加到现有类中.

The proper use of each, then, should be clear: Use protocols to declare a set of methods that a class must implement, and use categories to add methods to an existing class.

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