为什么有时会使用flutter_downloader下载失败? [英] Why do my downloads fail sometimes using flutter_downloader?

问题描述

我正在使用 flutter_downloader 插件为我的应用程序用户下载文件.在Android和iOS上，下载有时会失败，并显示以下错误消息: flutter:找不到与给定任务ID对应的任务.使用iOS，有时我的下载任务只会被排入队列，而根本不会执行.有时它们运行平稳.

I'm using the flutter_downloader plugin to download files for my app users. On both Android and iOS, downloads sometimes fail with this error message: flutter: not found task corresponding to given task id. With iOS, sometimes my download tasks would just be enqueued and not executed at all. Sometimes they run smoothly.

我发现运行 flutter clean 并重新构建应用程序似乎使这种情况消失了一点(下载成功并且可以在相关应用程序中打开文件)，但是当我在之后再次构建Flutter应用程序时改变某些东西，错误又回来了.我已启用Android明文流量，但无济于事.

I found that running flutter clean and rebuilding the app seems to make this disappear for a bit (download successful and file can be opened in relevant apps), but when I build the Flutter app again after changing something, the error comes back. I've enabled Android cleartext traffic, to no avail.

这是我的代码的最小复制:

Here's a minimal reproduction of my code:

import 'dart:isolate';
import 'dart:ui';

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

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

_initializeFlutterDownloader()async{
    WidgetsFlutterBinding.ensureInitialized();
await FlutterDownloader.initialize();
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Downloader Example',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Downloader Example'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  ReceivePort _port = ReceivePort();

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

  static void downloadCallback(
      String id, DownloadTaskStatus status, int progress) {
    final SendPort send =
        IsolateNameServer.lookupPortByName('downloader_send_port');
    send.send([id, status, progress]);
  }

  _downloadListener() {
    IsolateNameServer.registerPortWithName(
        _port.sendPort, 'downloader_send_port');
    _port.listen((dynamic data) {
      String id = data[0];
      DownloadTaskStatus status = data[1];
      if (status.toString() == "DownloadTaskStatus(3)") {
        FlutterDownloader.open(taskId: id);
      }
    });
    FlutterDownloader.registerCallback(downloadCallback);
  }

  void _download() async {
    String _localPath =
        (await findLocalPath()) + Platform.pathSeparator + 'Example_Downloads';

    final savedDir = Directory(_localPath);
    bool hasExisted = await savedDir.exists();
    if (!hasExisted) {
      savedDir.create();
    }
    String _url =
        "https://www.colonialkc.org/wp-content/uploads/2015/07/Placeholder.png";
    final download = await FlutterDownloader.enqueue(
      url: _url,
      savedDir: _localPath,
      showNotification: true,
      openFileFromNotification: true,
    );
  }

  Future<String> findLocalPath() async {
    final directory =
        // (MyGlobals.platform == "android")
        // ?
        await getExternalStorageDirectory();
    // : await getApplicationDocumentsDirectory();
    return directory.path;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _download,
        child: Icon(Icons.file_download),
      ),
    );
  }
}

这是我的 flutter医生结果:

[✓] Flutter (Channel stable, v1.12.13+hotfix.5, on Mac OS X 10.14.6 18G95, locale en-ID)
    • Flutter version 1.12.13+hotfix.5 at /Users/ictmacbook2/flutter
    • Framework revision 27321ebbad (3 months ago), 2019-12-10 18:15:01 -0800
    • Engine revision 2994f7e1e6
    • Dart version 2.7.0


[✓] Android toolchain - develop for Android devices (Android SDK version 29.0.3)
    • Android SDK at /Users/ictmacbook2/Library/Android/sdk
    • Android NDK location not configured (optional; useful for native profiling support)
    • Platform android-29, build-tools 29.0.3
    • Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 1.8.0_202-release-1483-b49-5587405)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 10.3)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 10.3, Build version 10G8
    • CocoaPods version 1.7.5

[✓] Android Studio (version 3.5)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin version 43.0.1
    • Dart plugin version 191.8593
    • Java version OpenJDK Runtime Environment (build 1.8.0_202-release-1483-b49-5587405)

[✓] VS Code (version 1.42.1)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.8.1

[✓] Connected device (1 available)
    • iPad • 1ba96acf871024d9097348342ff6d84fe5013c16 • ios • iOS 12.4.1

• No issues found!

推荐答案

根据此问题我在GitHub上打开，我将 if 从 if(status.toString()=="DownloadTaskStatus(3)")更改为if(status.toString()=="DownloadTaskStatus(3)"&& progress == 100& id！= null).

According to the suggestions on this issue I opened on GitHub, I changed my if from if (status.toString() == "DownloadTaskStatus(3)") to if (status.toString() == "DownloadTaskStatus(3)" && progress == 100 &&id!=null).

出于很好的考虑，我还查询了我们在 downloadListener 函数中正在寻找的特定任务，如下所示:

For good measure, I also queried for the specific task we're looking for in my downloadListener function, like so:

  _downloadListener() {
    IsolateNameServer.registerPortWithName(_port.sendPort, 'downloader_send_port');
    _port.listen((dynamic data) {
      String id = data[0];
      DownloadTaskStatus status = data[1];
      int progress = data[2];
      if (status.toString() == "DownloadTaskStatus(3)" && progress == 100 && id != null) {
          String query = "SELECT * FROM task WHERE task_id='" + id + "'";
          var tasks = FlutterDownloader.loadTasksWithRawQuery(query: query);
          //if the task exists, open it
          if (tasks != null) FlutterDownloader.open(taskId: id);
      }
    });
    FlutterDownloader.registerCallback(downloadCallback);
  }

现在一切运行顺利.请注意，每当我进行热刷新时，任务都将被排队，而不执行.必须中止并重建应用程序，下载才能再次正常运行.

It all runs smoothly now. Just a note, whenever I hot refresh, the tasks would just be enqueued and not executed. Had to abort and rebuild the app for the downloads to work properly again.

这篇关于为什么有时会使用flutter_downloader下载失败?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！