此语法与接口声明有关意味着什么? [英] What does this syntax mean relating to interface declaration?

问题描述

这是来自游戏教程的入门项目中的ViewController.m文件.

This is from the ViewController.m file in a starter project from a tutorial for a game.

@interface ViewController()

//irrelevant stuff omitted

@end

是让我感到困惑的是ViewController()位.我了解公共接口和私有接口之间的区别，但是直到现在在Objective-C中我还没有使用私有接口.我曾经在公共界面上看到过这样的东西:

It's the ViewController() bit that confuses me. I understand the different between public and private interfaces, but I haven't used a private interface til now in Objective-C. I'm used to seeing something like this instead, for the public interface:

@interface ViewController : UIViewController

那么为什么现在它只是第一个带有括号且没有继承符号的?

So why now is it just the first one, and with parentheses, with no inheritance notation?

推荐答案

这是

That's a class extension. It allows for declaring additional interface, usually private because it's in an implementation (.m) file. It's similar to a category, except that the compiler will require you to supply the implementation for any interface declared within it. (A category can declare an interface even if nothing provides any implementation.)

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