"show" 和有什么不一样?和“作为"在导入语句中? [英] What is the difference between "show" and "as" in an import statement?

问题描述

import 语句中的 show 和 as 有什么区别?

What is the difference between show and as in an import statement?

比如有什么区别

import 'dart:convert' show JSON;

和

import 'package:google_maps/google_maps.dart' as GoogleMap;

什么时候用show，什么时候用as?

When do I use show and when should I use as?

如果我切换到 show GoogleMap，所有对 GoogleMap(例如 GoogleMap.LatLng)对象的引用都被报告为未定义.

If I switch to show GoogleMap all references to GoogleMap (e.g. GoogleMap.LatLng) objects are reported as undefined.

推荐答案

as 和 show 是两个不同的概念.

as and show are two different concepts.

使用 as 为导入的库命名.如果一个库有很多全局函数，通常这样做是为了防止它污染你的命名空间.如果您使用 as，您可以按照您在示例中的方式访问所述库的所有函数和类:GoogleMap.LatLng.

With as you are giving the imported library a name. It's usually done to prevent a library from polluting your namespace if it has a lot of global functions. If you use as you can access all functions and classes of said library by accessing them the way you did in your example: GoogleMap.LatLng.

使用 show(和 hide)，您可以选择要在应用程序中显示的特定类.对于您的示例，它将是:

With show (and hide) you can pick specific classes you want to be visible in your application. For your example it would be:

import 'package:google_maps/google_maps.dart' show LatLng;

有了这个，您将能够访问LatLng，但不能访问该库中的其他内容.与此相反的是:

With this you would be able to access LatLng but nothing else from that library. The opposite of this is:

import 'package:google_maps/google_maps.dart' hide LatLng;

有了这个，您将能够访问该库中除LatLng 之外的所有内容.

With this you would be able to access everything from that library except for LatLng.

如果你想使用多个同名的类，你需要使用as.您也可以结合使用这两种方法:

If you want to use multiple classes with the same name you'd need to use as. You also can combine both approaches:

import 'package:google_maps/google_maps.dart' as GoogleMap show LatLng;

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