id< protocol>之间的区别和NSObject<协议> [英] Difference between id<protocol> and NSObject<protocol>

问题描述

在Objective-C中， id< protocol>或NSObject< protocol>

In Objective-C, id<protocol> or NSObject<protocol> are frequently used for delegate declaration.

id和NSObject之间的主要区别是什么？
你什么时候想使用一个对方？

What are the main differences between id and NSObject? When do you want to use one versus the other?

推荐答案

id< protocol> obj 是符合指定协议的任何对象的声明。
您可以将给定协议的任何消息发送到对象（或从< protocol> 继承的协议
）。

id<protocol> obj is the declaration for any object that conforms to the specified protocol. You can send any message from the given protocol to the object (or from the protocols that <protocol> inherits from).

NSObject< protocol> * obj 是任何对象的声明，

• 符合给定的协议，


• 派生自 NSObject 。

• conforms to the given protocol, and
• is derived from NSObject.

这意味着在第二种情况下，您可以将 NSObject class
中的任何方法发送到对象，例如

That means that in the second case, you can send any methods from the NSObject class to the object, for example

id y = [obj copy];

这将在第一种情况下给出编译器错误。

which would give a compiler error in the first case.

第二个声明还意味着 obj 符合 NSObject 协议 。
但是如果< protocol> 是从NSObject协议派生的，那么这不会有什么区别：

The second declaration also implies that obj conforms to the NSObject protocol. But this makes no difference if <protocol> is derived from the NSObject protocol:

@protocol protocol <NSObject>

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