无法使用 flutter_downloader 下载答案

【问题标题】：Can't download using flutter_downloader无法使用 flutter_downloader 下载
【发布时间】：2019-09-10 14:53:55
【问题描述】：

我正在尝试在我的颤振应用程序中使用颤振下载器。但是，当我触发下载操作时出现以下错误：

D/permissions_handler(16054): No permissions found in manifest for: $permission
D/permissions_handler(16054): No permissions found in manifest for: $permission
I/flutter (16054): decodePermissionRequestResult called with: value:[{14: 4}]
W/WM-WorkSpec(16054): Backoff delay duration less than minimum value
E/MethodChannel#vn.hunghd/downloader(16054): Failed to handle method call
E/MethodChannel#vn.hunghd/downloader(16054): java.lang.IllegalStateException: WorkManager is not initialized properly.  The most likely cause is that you disabled WorkManagerInitializer in your manifest but forgot to call WorkManager#initialize in your Application#onCreate or a ContentProvider.
E/MethodChannel#vn.hunghd/downloader(16054):    at androidx.work.WorkManager.getInstance(WorkManager.java:141)
E/MethodChannel#vn.hunghd/downloader(16054):    at vn.hunghd.flutterdownloader.FlutterDownloaderPlugin.enqueue(FlutterDownloaderPlugin.java:175)
E/MethodChannel#vn.hunghd/downloader(16054):    at vn.hunghd.flutterdownloader.FlutterDownloaderPlugin.onMethodCall(FlutterDownloaderPlugin.java:73)
E/MethodChannel#vn.hunghd/downloader(16054):    at io.flutter.plugin.common.MethodChannel$IncomingMethodCallHandler.onMessage(MethodChannel.java:201)
E/MethodChannel#vn.hunghd/downloader(16054):    at io.flutter.view.FlutterNativeView$PlatformMessageHandlerImpl.handleMessageFromDart(FlutterNativeView.java:188)
E/MethodChannel#vn.hunghd/downloader(16054):    at io.flutter.embedding.engine.FlutterJNI.handlePlatformMessage(FlutterJNI.java:202)
E/MethodChannel#vn.hunghd/downloader(16054):    at android.os.MessageQueue.nativePollOnce(Native Method)
E/MethodChannel#vn.hunghd/downloader(16054):    at android.os.MessageQueue.next(MessageQueue.java:326)
E/MethodChannel#vn.hunghd/downloader(16054):    at android.os.Looper.loop(Looper.java:160)
E/MethodChannel#vn.hunghd/downloader(16054):    at android.app.ActivityThread.main(ActivityThread.java:6669)
E/MethodChannel#vn.hunghd/downloader(16054):    at java.lang.reflect.Method.invoke(Native Method)
E/MethodChannel#vn.hunghd/downloader(16054):    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
E/MethodChannel#vn.hunghd/downloader(16054):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
I/flutter (16054): Download task is failed with reason(WorkManager is not initialized properly.  The most likely cause is that you disabled WorkManagerInitializer in your manifest but forgot to call WorkManager#initialize in your Application#onCreate or a ContentProvider.)
W/5gmail.playlis(16054): Accessing hidden method Ldalvik/system/CloseGuard;->close()V (light greylist, linking)

这是我的下载管理器类。

import 'package:flutter_downloader/flutter_downloader.dart';
import 'package:path_provider/path_provider.dart';
import 'package:permission_handler/permission_handler.dart';

class DownloadManager {
  Future<bool> checkPermission() async {
    PermissionStatus permission = await PermissionHandler()
        .checkPermissionStatus(PermissionGroup.storage);
    if (permission != PermissionStatus.granted) {
      Map<PermissionGroup, PermissionStatus> permissions =
      await PermissionHandler()
          .requestPermissions([PermissionGroup.storage]);
      if (permissions[PermissionGroup.storage] == PermissionStatus.granted) {
        return true;
      }
    }
    return false;
  }

  void inti(String url) async {
    await checkPermission();
    final directory = await getExternalStorageDirectory();
    final taskId = await FlutterDownloader.enqueue(
      url: url,
      savedDir: directory.toString(),
      showNotification: true, // show download progress in status bar (for Android)
      openFileFromNotification: true, // click on notification to open downloaded file (for Android)
    );
    FlutterDownloader.registerCallback((id, status,progress) {
      print(
          'Download task ($id) is in status ($status) and process ($progress)');
    });
  }
}

我正在使用这个插件flutter_downloader。

谁能帮忙？

【问题讨论】：

标签： android flutter

【解决方案1】：

尝试添加这个

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

还有

 android:requestLegacyExternalStorage="true"

在您的 AndroidManifest.xml 中将起作用

【讨论】：

【解决方案2】：

我建议你使用 Dart 下载文件。

您只需注册您的应用即可支持 Android 和 iOS 上的后台工作。

在flutter_workmanager插件的帮助下，这相对容易。
您可以注册您的应用程序，以便在需要运行时在 Dart 代码中接收回调。

例如：

void callbackDispatcher() {
  Workmanager.executeTask((backgroundTask) {
    switch(backgroundTask) {
      case "downloadMyFile":
        print("You are now in a background Isolate");
        print("Download your file here using Dart");
        HttpClient client = new HttpClient();
        var _downloadData = List<int>();
        var fileSave = new File('./logo.png');
        client.getUrl(
            Uri.parse("https://fluttermaster.com/wp-content/uploads/2018/08/fluttermaster.com-logo-web-header.png"))
            .then((HttpClientRequest request) {
          return request.close();
        })
            .then((HttpClientResponse response) {
          response.listen((d) => _downloadData.addAll(d),
              onDone: () {
                fileSave.writeAsBytes(_downloadData);
              }
          );
        });
        break;
    }
    return Future.value(true);
  });
}

void main() {
  Workmanager.initialize(callbackDispatcher);
  Workmanager.registerOneOffTask("1", "downloadMyFile");
  runApp(MyApp());
}

【讨论】：

【解决方案3】：

尝试将<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" /> 添加到AndroidManifest.xml

【讨论】：