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 仅在Android / iOS上有效，我有条件地从文件中排除以下导入：

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"

的方式如下：

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，此只能在Flutter中导入用于移动设备的库。详细信息此处（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');
         }
     }
 }

此天真的尝试在 AudioCache 参考。

This naive try fails on AudioCache reference of course.

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

推荐答案

在此堆栈中问题，它与您的要求类似，我基于 http package。

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

我想您也可以使用类似的方法来处理这种条件依赖。我提供了一个有效的示例有。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。

The core idea is as follows.

1. 创建一个抽象类来定义一般需要使用的方法。


2. 创建特定于 web 和<$ c $的实现c> android 依赖项扩展了这个抽象类。


3. 创建一个存根，该存根公开一个方法来返回此抽象实现的实例。


4. 在抽象类中，导入此存根文件以及特定于 mobile 和 web 。然后在其工厂构造函数中返回特定实现的实例。如果书写正确，则将自动通过条件导入进行处理。



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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