Flutter资源下载插件download_assets的使用

download_assets 是一个强大的库，用于在应用程序中下载资源文件（如图片、视频等）。它提供了简单易用的接口来处理下载和解压缩的过程。

关于

download_assets 包可以帮助开发者轻松地将各种类型的文件下载到应用中，并提供了一系列方法来管理下载过程中的状态和进度。

功能

初始化

首先需要初始化 DownloadAssetsController，设置资产目录：

await downloadAssetsController.init();

开始下载

开始下载资源文件：

await downloadAssetsController.startDownload(
    onCancel: () {
        // 用户取消下载时的操作
    },
    assetsUrls: [
      'https://github.com/edjostenes/download_assets/raw/main/download/image_1.png',
      'https://github.com/edjostenes/download_assets/raw/main/download/assets.zip',
      'https://github.com/edjostenes/download_assets/raw/main/download/image_2.png',
      'https://github.com/edjostenes/download_assets/raw/main/download/image_3.png',
    ],
    onProgress: (progressValue) {
        // 下载进度更新
    },
    onDone: () {
      // 下载完成后的操作
    }
);

清除已下载的资源

可以调用以下方法清除本地存储的所有下载资源：

await downloadAssetsController.clearAssets();

获取资源目录路径

获取资源文件的存储路径：

File('${downloadAssetsController.assetsDir}/<file_name>.<file_extension>');

检查资源目录是否存在

检查资源目录是否已经存在：

return await downloadAssetsController.assetsDirAlreadyExists();

检查特定文件是否存在

检查某个文件是否已经下载：

return await downloadAssetsController.assetsFileExists(<file_name>);

解压委托

为了支持不同类型的压缩文件（如ZIP、RAR等），你可以实现自定义的解压委托：

abstract class UncompressDelegate {
  const UncompressDelegate();

  String get extension;

  Future uncompress(String compressedFilePath, String assetsDir);
}

示例代码

下面是一个完整的示例，展示了如何使用 download_assets 插件：

import 'dart:io';
import 'package:download_assets/download_assets.dart';
import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) => MaterialApp(
        debugShowCheckedModeBanner: false,
        title: 'Download Assets Demo',
        theme: ThemeData(
          primarySwatch: Colors.blue,
          visualDensity: VisualDensity.adaptivePlatformDensity,
        ),
        home: MyHomePage(title: 'Download Assets'),
      );
}

class MyHomePage extends StatefulWidget {
  MyHomePage({required this.title});

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  DownloadAssetsController downloadAssetsController = DownloadAssetsController();
  String message = 'Press the download button to start the download';
  bool downloaded = false;
  double value = 0.0;

  @override
  void initState() {
    super.initState();
    _init();
  }

  Future _init() async {
    await downloadAssetsController.init();
    downloaded = await downloadAssetsController.assetsDirAlreadyExists();
  }

  @override
  Widget build(BuildContext context) => Scaffold(
        appBar: AppBar(
          title: Text(widget.title),
        ),
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              if (downloaded) ...[
                Container(
                  width: 150,
                  height: 150,
                  decoration: BoxDecoration(
                    image: DecorationImage(
                      image: FileImage(File('${downloadAssetsController.assetsDir}/dart.jpeg')),
                      fit: BoxFit.fitWidth,
                    ),
                  ),
                ),
                Container(
                  width: 150,
                  height: 150,
                  decoration: BoxDecoration(
                    image: DecorationImage(
                      image: FileImage(File('${downloadAssetsController.assetsDir}/flutter.png')),
                      fit: BoxFit.fitWidth,
                    ),
                  ),
                ),
              ],
              TweenAnimationBuilder<double>(
                duration: const Duration(milliseconds: 250),
                curve: Curves.easeInOut,
                tween: Tween<double>(
                  begin: 0,
                  end: value,
                ),
                builder: (context, value, _) => LinearProgressIndicator(
                  minHeight: 10,
                  value: value,
                ),
              ),
              Text(
                message,
                textAlign: TextAlign.center,
              ),
            ],
          ),
        ),
        floatingActionButton: Row(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            FloatingActionButton(
              onPressed: _downloadAssets,
              tooltip: 'Download',
              child: Icon(Icons.arrow_downward),
            ),
            const SizedBox(
              width: 25,
            ),
            FloatingActionButton(
              onPressed: () async {
                await downloadAssetsController.clearAssets();
                await _downloadAssets();
              },
              tooltip: 'Refresh',
              child: Icon(Icons.refresh),
            ),
            const SizedBox(
              width: 25,
            ),
            FloatingActionButton(
              onPressed: _cancel,
              tooltip: 'Cancel',
              child: Icon(Icons.cancel_outlined),
            ),
          ],
        ),
      );

  Future _downloadAssets() async {
    final assetsDownloaded = await downloadAssetsController.assetsDirAlreadyExists();

    if (assetsDownloaded) {
      setState(() {
        message = 'Click in refresh button to force download';
        print(message);
      });
      return;
    }

    try {
      value = 0.0;
      downloaded = false;
      await downloadAssetsController.startDownload(
          onCancel: () {
            message = 'Cancelled by user';
            setState(() {});
          },
          assetsUrls: [
            'https://github.com/edjostenes/download_assets/raw/main/download/image_1.png',
            'https://github.com/edjostenes/download_assets/raw/main/download/assets.zip',
            'https://github.com/edjostenes/download_assets/raw/main/download/image_2.png',
            'https://github.com/edjostenes/download_assets/raw/main/download/image_3.png',
          ],
          onProgress: (progressValue) {
            value = progressValue;
            setState(() {
              message = 'Downloading - ${(progressValue * 100).toStringAsFixed(2)}';
              print(message);
            });
          },
          onDone: () {
            setState(() {
              downloaded = true;
              message = 'Download completed\nClick in refresh button to force download';
            });
          });
    } on DownloadAssetsException catch (e) {
      print(e.toString());
      setState(() {
        downloaded = false;
        message = 'Error: ${e.toString()}';
      });
    }
  }

  void _cancel() => downloadAssetsController.cancelDownload();
}

以上代码展示了如何在Flutter应用中使用 download_assets 插件进行资源下载和管理。希望这个示例能帮助你更好地理解和使用该插件。