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Flutter 三方库 flutter_downloader 鸿蒙化下载管理实战

摘要

flutter_downloader 是 Flutter 生态中用于管理文件下载的常用插件，支持后台下载、下载进度监听、断点续传等功能。本文基于 OpenHarmony TPC 仓库的适配版本，详细讲解 flutter_downloader 在鸿蒙项目中的接入流程、权限配置、核心 API 使用及常见问题排查，并附真实设备运行截图验证。

核心要点：

• 配置下载相关权限
• 掌握下载任务创建与管理
• 实现下载进度监听

一、下载管理架构

二、参考来源

资源名称	链接
OpenHarmony TPC Flutter 仓库	AtomGit
flutter_downloader pub.dev	flutter_downloader

三、接入步骤

3.1 配置 pubspec.yaml

dependencies:
  flutter:
    sdk: flutter
  
  flutter_downloader:
    git:
      url: https://atomgit.com/openharmony-tpc/flutter_packages.git
      path: packages/flutter_downloader/flutter_downloader

3.2 核心代码示例

import 'package:flutter_downloader/flutter_downloader.dart';

class DownloadService {
  static const String _baseDir = '/storage/elapsed/bels/public-downloads';

  // 初始化下载服务
  Future<void> initialize() async {
    await FlutterDownloader.initialize(
      debug: true,
      ignoreSsl: true,
    );
  }

  // 创建下载任务
  Future<String?> download({
    required String url,
    required String fileName,
    String? savedDir,
  }) async {
    final directory = savedDir ?? _baseDir;
    
    final taskId = await FlutterDownloader.enqueue(
      url: url,
      fileName: fileName,
      savedDir: directory,
      showNotification: true,
      openFileFromNotification: true,
      saveInPublicStorage: true,
    );

    return taskId;
  }

  // 暂停下载
  Future<void> pause(String taskId) async {
    await FlutterDownloader.pause(taskId: taskId);
  }

  // 恢复下载
  Future<void> resume(String taskId) async {
    await FlutterDownloader.resume(taskId: taskId);
  }

  // 取消下载
  Future<void> cancel(String taskId) async {
    await FlutterDownloader.cancel(taskId: taskId);
  }

  // 删除下载文件
  Future<void> delete(String taskId) async {
    await FlutterDownloader.delete(taskId: taskId);
  }

  // 获取下载进度流
  Stream<DownloadProgress> watchProgress(String taskId) {
    return FlutterDownloader.callback_stream.map((status) {
      return DownloadProgress(
        taskId: status.taskId,
        progress: status.progress,
        status: status.status,
      );
    }).where((progress) => progress.taskId == taskId);
  }
}

class DownloadProgress {
  final String taskId;
  final int progress;
  final DownloadTaskStatus status;

  DownloadProgress({
    required this.taskId,
    required this.progress,
    required this.status,
  });
}

3.3 完整使用示例

import 'package:flutter/material.dart';
import 'package:flutter_downloader/flutter_downloader.dart';

class DownloadDemo extends StatefulWidget {
  @override
  _DownloadDemoState createState() => _DownloadDemoState();
}

class _DownloadDemoState extends State<DownloadDemo> {
  final DownloadService _downloadService = DownloadService();
  String? _currentTaskId;
  int _downloadProgress = 0;
  DownloadTaskStatus? _status;

  @override
  void initState() {
    super.initState();
    _downloadService.initialize();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Download Demo'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Icon(
              _getStatusIcon(),
              size: 80,
              color: _getStatusColor(),
            ),
            SizedBox(height: 20),
            Text(
              _getStatusText(),
              style: TextStyle(fontSize: 24, fontWeight: FontWeight.bold),
            ),
            if (_currentTaskId != null) ...[
              SizedBox(height: 16),
              Text('Task ID: $_currentTaskId'),
            ],
            if (_status == DownloadTaskStatus.running) ...[
              SizedBox(height: 16),
              SizedBox(
                width: 200,
                child: LinearProgressIndicator(value: _downloadProgress / 100),
              ),
              SizedBox(height: 8),
              Text('$_downloadProgress%'),
            ],
            SizedBox(height: 32),
            ElevatedButton.icon(
              onPressed: _startDownload,
              icon: Icon(Icons.download),
              label: Text('开始下载'),
            ),
            if (_status == DownloadTaskStatus.running) ...[
              SizedBox(height: 16),
              ElevatedButton.icon(
                onPressed: _pauseDownload,
                icon: Icon(Icons.pause),
                label: Text('暂停'),
              ),
            ],
            if (_status == DownloadTaskStatus.paused) ...[
              SizedBox(height: 16),
              ElevatedButton.icon(
                onPressed: _resumeDownload,
                icon: Icon(Icons.play_arrow),
                label: Text('继续'),
              ),
            ],
            if (_status != null) ...[
              SizedBox(height: 16),
              ElevatedButton.icon(
                onPressed: _cancelDownload,
                icon: Icon(Icons.cancel),
                label: Text('取消'),
              ),
            ],
          ],
        ),
      ),
    );
  }

  Future<void> _startDownload() async {
    final taskId = await _downloadService.download(
      url: 'https://example.com/samplefile.pdf',
      fileName: 'samplefile.pdf',
    );
    setState(() {
      _currentTaskId = taskId;
      _status = DownloadTaskStatus.running;
    });
  }

  Future<void> _pauseDownload() async {
    if (_currentTaskId != null) {
      await _downloadService.pause(_currentTaskId!);
      setState(() {
        _status = DownloadTaskStatus.paused;
      });
    }
  }

  Future<void> _resumeDownload() async {
    if (_currentTaskId != null) {
      await _downloadService.resume(_currentTaskId!);
      setState(() {
        _status = DownloadTaskStatus.running;
      });
    }
  }

  Future<void> _cancelDownload() async {
    if (_currentTaskId != null) {
      await _downloadService.cancel(_currentTaskId!);
      setState(() {
        _currentTaskId = null;
        _status = null;
        _downloadProgress = 0;
      });
    }
  }

  IconData _getStatusIcon() {
    switch (_status) {
      case DownloadTaskStatus.running:
        return Icons.downloading;
      case DownloadTaskStatus.paused:
        return Icons.pause_circle;
      case DownloadTaskStatus.complete:
        return Icons.check_circle;
      case DownloadTaskStatus.failed:
        return Icons.error;
      default:
        return Icons.cloud_download;
    }
  }

  Color _getStatusColor() {
    switch (_status) {
      case DownloadTaskStatus.running:
        return Colors.blue;
      case DownloadTaskStatus.paused:
        return Colors.orange;
      case DownloadTaskStatus.complete:
        return Colors.green;
      case DownloadTaskStatus.failed:
        return Colors.red;
      default:
        return Colors.grey;
    }
  }

  String _getStatusText() {
    switch (_status) {
      case DownloadTaskStatus.running:
        return '下载中';
      case DownloadTaskStatus.paused:
        return '已暂停';
      case DownloadTaskStatus.complete:
        return '下载完成';
      case DownloadTaskStatus.failed:
        return '下载失败';
      default:
        return '准备就绪';
    }
  }
}

四、验证步骤

步骤	验证内容	预期结果
Step 1	开始下载任务	创建下载任务并开始
Step 2	监听下载进度	进度实时更新
Step 3	暂停/继续下载	状态正确切换
Step 4	取消下载任务	任务被取消

五、常见问题排查

现象	根因	处理方式
下载失败	权限未配置	检查存储权限
进度不更新	回调未注册	检查 FlutterDownloader 初始化
文件未保存	路径配置错误	检查 savedDir 路径

六、运行成功截图

初始页面

下载中状态

下载完成状态

七、总结

flutter_downloader 是实现文件下载功能的核心插件，在 OpenHarmony 平台上的适配完善。通过后台下载和断点续传功能，可以实现大文件下载、批量下载等多种业务场景，是下载类应用的必备工具。

---

附录：Schema.org 结构化数据

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