dart_http_downloader 是一个用于在 Flutter 应用中管理文件下载的插件。它提供了简单易用的 API，允许你下载文件、暂停、恢复、取消下载，并管理下载任务的状态。

安装

首先，你需要在 pubspec.yaml 文件中添加 dart_http_downloader 依赖：

dependencies:
  flutter:
    sdk: flutter
  dart_http_downloader: ^1.0.0  # 请使用最新版本

然后运行 flutter pub get 来安装依赖。

基本用法

1. 初始化下载器

在使用 dart_http_downloader 之前，你需要初始化下载器：

import 'package:dart_http_downloader/dart_http_downloader.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await DartHttpDownloader.initialize();
  runApp(MyApp());
}

2. 下载文件

你可以使用 DartHttpDownloader.download 方法来下载文件：

void downloadFile() async {
  String url = 'https://example.com/file.zip';
  String savePath = '/path/to/save/file.zip';

  DownloadTask task = await DartHttpDownloader.download(
    url,
    savePath,
    onProgress: (progress) {
      print('Download progress: ${progress * 100}%');
    },
  );

  print('Download task started with id: ${task.taskId}');
}

3. 暂停、恢复和取消下载

你可以通过 taskId 来管理下载任务：

void pauseDownload(String taskId) async {
  await DartHttpDownloader.pause(taskId);
  print('Download paused');
}

void resumeDownload(String taskId) async {
  await DartHttpDownloader.resume(taskId);
  print('Download resumed');
}

void cancelDownload(String taskId) async {
  await DartHttpDownloader.cancel(taskId);
  print('Download canceled');
}

4. 监听下载状态

你可以通过 DartHttpDownloader.listen 来监听下载任务的状态：

void listenToDownloadStatus() {
  DartHttpDownloader.listen((DownloadTask task) {
    switch (task.status) {
      case DownloadTaskStatus.running:
        print('Task ${task.taskId} is running');
        break;
      case DownloadTaskStatus.paused:
        print('Task ${task.taskId} is paused');
        break;
      case DownloadTaskStatus.completed:
        print('Task ${task.taskId} is completed');
        break;
      case DownloadTaskStatus.canceled:
        print('Task ${task.taskId} is canceled');
        break;
      case DownloadTaskStatus.failed:
        print('Task ${task.taskId} failed with error: ${task.error}');
        break;
    }
  });
}

5. 获取所有下载任务

你可以获取所有当前的下载任务：

void getAllTasks() async {
  List<DownloadTask> tasks = await DartHttpDownloader.getAllTasks();
  tasks.forEach((task) {
    print('Task ID: ${task.taskId}, Status: ${task.status}');
  });
}

完整示例

以下是一个完整的示例，展示了如何使用 dart_http_downloader 下载文件并管理下载任务：

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

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await DartHttpDownloader.initialize();
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: DownloadPage(),
    );
  }
}

class DownloadPage extends StatefulWidget {
  @override
  _DownloadPageState createState() => _DownloadPageState();
}

class _DownloadPageState extends State<DownloadPage> {
  String taskId;

  void downloadFile() async {
    String url = 'https://example.com/file.zip';
    String savePath = '/path/to/save/file.zip';

    DownloadTask task = await DartHttpDownloader.download(
      url,
      savePath,
      onProgress: (progress) {
        print('Download progress: ${progress * 100}%');
      },
    );

    setState(() {
      taskId = task.taskId;
    });

    print('Download task started with id: $taskId');
  }

  void pauseDownload() async {
    if (taskId != null) {
      await DartHttpDownloader.pause(taskId);
      print('Download paused');
    }
  }

  void resumeDownload() async {
    if (taskId != null) {
      await DartHttpDownloader.resume(taskId);
      print('Download resumed');
    }
  }

  void cancelDownload() async {
    if (taskId != null) {
      await DartHttpDownloader.cancel(taskId);
      print('Download canceled');
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('File Downloader'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            ElevatedButton(
              onPressed: downloadFile,
              child: Text('Download File'),
            ),
            ElevatedButton(
              onPressed: pauseDownload,
              child: Text('Pause Download'),
            ),
            ElevatedButton(
              onPressed: resumeDownload,
              child: Text('Resume Download'),
            ),
            ElevatedButton(
              onPressed: cancelDownload,
              child: Text('Cancel Download'),
            ),
          ],
        ),
      ),
    );
  }
}

注意事项

1. 权限：在 Android 上，你需要确保应用有写入外部存储的权限。你可以在 AndroidManifest.xml 中添加以下权限：

   <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>