Swift 3 - 动态 vs @objc [英] Swift 3 - dynamic vs @objc

问题描述

将方法标记为@objc 与动态之间有什么区别，你会在什么时候做一个和另一个?

What's the difference between marking a method as @objc vs dynamic, when would you do one vs the other?

以下是 Apple 对动态的定义.

Below is Apple's definition for dynamic.

dynamic 将此修饰符应用于类的任何成员，该成员可以以Objective-C为代表.当你标记一个成员声明时动态修饰符，对该成员的访问始终是动态的使用 Objective-C 运行时调度.对该成员的访问是从未被编译器内联或去虚拟化.

dynamic Apply this modifier to any member of a class that can be represented by Objective-C. When you mark a member declaration with the dynamic modifier, access to that member is always dynamically dispatched using the Objective-C runtime. Access to that member is never inlined or devirtualized by the compiler.

因为用 dynamic 修饰符标记的声明被分派使用 Objective-C 运行时，它们被隐式标记为 objc属性.

Because declarations marked with the dynamic modifier are dispatched using the Objective-C runtime, they’re implicitly marked with the objc attribute.

推荐答案

声明为 @objc 的函数/变量可从 Objective-C 访问，但 Swift 将继续通过静态或虚拟调度.这意味着如果函数/变量通过 Objective-C 框架进行了调整，就像使用 Key-Value Observing 或各种 Objective-C API 修改类时发生的情况一样，从 Swift 和 Objective-C 调用方法会产生不同的结果.

A function/variable declared as @objc is accessible from Objective-C, but Swift will continue to access it directly via static or virtual dispatch. This means if the function/variable is swizzled via the Objective-C framework, like what happens when using Key-Value Observing or the various Objective-C APIs to modify classes, calling the method from Swift and Objective-C will produce different results.

使用 dynamic 告诉 Swift 总是引用 Objective-C 动态调度.这是关键值观察等正常工作所必需的.调用 Swift 函数时，会参考 Objective-C 运行时动态调度调用.

Using dynamic tells Swift to always refer to Objective-C dynamic dispatch. This is required for things like Key-Value Observing to work correctly. When the Swift function is called, it refers to the Objective-C runtime to dynamically dispatch the call.

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