Flutter - flutter-web 中的条件库导入 [英] Flutter - Conditional library import in flutter-web

问题描述

假设 audioplayers|lib/audio_cache.dart 仅适用于 Android/iOS，我有条件地排除以下从 Dart 文件导入:

Supposing that audioplayers|lib/audio_cache.dart worked only on Android/iOS, I conditionally exclude the following import from a Dart file:

import "package:audioplayers/audio_cache.dart"

通过以下方式:

import "dart:math" if (dart.library.io) "package:audioplayers/audio_cache.dart";

其中dart:math"可以是任何 fake_stub Dart 文件.简而言之，这在 Flutter 中导入仅适用于移动设备的库.详情此处(感谢Alois Deniel！).

where "dart:math" can be any fake_stub Dart file. In short this imports a library only for mobile devices in Flutter. Details here (thanks Alois Deniel!).

在 Flutter-Web 实现中隐藏平台特定代码的最佳方法是什么?

What would be the best way to hide platform-specific code in Flutter-Web implementation?

 import 'dart:io' show Platform;

 bool isMobile() => Platform.isAndroid || Platform.isIOS;

 class _MyPageState extends State<MyPage> {
     dynamic _audioPlayer;

     @override
     void initState() {
         if (isMobile()) {
            _audioPlayer = AudioCache(prefix: 'sounds/');
            _audioPlayer.load('mysound.mp3');
         }
     }
 }

当然，这个天真的尝试在 AudioCache 参考上失败了.

This naive try fails on AudioCache reference of course.

 Error: Method not found: 'AudioCache'.
  _audioPlayer = AudioCache(prefix: 'sounds/');

推荐答案

In this stack overflow 问题 与您的要求相似，我根据 http 包.

In this stack overflow question which has similar requirements as yours, I wrote an answer based on this implementation from http package.

我认为您也可以使用类似的方法来处理这种条件依赖关系.我在那里提供了一个工作示例.我在这里引用答案.

I think you can also use a similar approach to handle this conditional dependencies. I have provided a working example there. I am quoting the answer here.

核心思想如下.

1. 创建一个抽象类来定义您需要在一般情况下使用的方法.
2. 创建扩展此抽象类的特定于 web 和 android 依赖项的实现.
3. 创建一个存根，它公开一个方法来返回这个抽象实现的实例.这只是为了让 dart 分析工具满意.
4. 在抽象类中导入此存根文件以及特定于 mobile 和 web 的条件导入.然后在其工厂构造函数中返回具体实现的实例.如果写入正确，这将通过条件导入自动处理.

1. Create an abstract class to define the methods you will need to use in genral.
2. Create implementations specific to web and android dependencies which extends this abstract class.
3. Create a stub which exposes a method to return the instance of this abstract implementation. This is only to keep the dart analysis tool happy.
4. In the abstract class import this stub file along with the conditional imports specific for mobile and web. Then in its factory constructor return the instance of the specific implementation. This will be handled automatically by conditional import if written correctly.

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