“显示”和“显示”之间有什么区别？和“为”在进口声明中？ [英] What is the difference between "show" and "as" in an import statement?

问题描述

导入语句中的 show 和 as 有什么区别？

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

例如，

import 'dart:convert' show JSON;

和

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

何时使用 show 以及何时使用我使用作为吗？

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

如果我切换到显示GoogleMap 对 GoogleMap （例如 GoogleMap.LatLng ）对象的所有引用均报告为未定义。

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 是两个不同的地方

通过 as ，您可以为导入的库命名。如果库具有许多全局函数，通常可以这样做以防止库污染您的命名空间。如果您将用作，则可以通过按示例中的方式访问它们来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.

具有显示（和隐藏），您可以选择想要在应用程序中显示的特定类。例如，

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;

使用此功能，您可以访问 LatLng 但该库中没有其他内容。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;

使用此方法，您可以访问该库中的所有内容，但 LatLng 。

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

如果要使用相同名称的多个类，则需要使用作为。您还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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