Flutter：在外部存储路径上创建目录 - 路径提供程序 getExternalStorageDirectory()

Question

我正在创建一个 flutter 应用程序，我想在其中下载图像并将其存储到外部存储（不是文档目录），以便任何照片库应用程序都可以查看它。 我正在使用以下代码创建一个目录

var dir = await getExternalStorageDirectory();
  if(!Directory("${dir.path}/myapp").existsSync()){
    Directory("${dir.path}/myapp").createSync(recursive: true);
  }

它给我以下错误：

FileSystemException: Creation failed, path = '/storage/emulated/0/myapp' (OS Error: Permission denied, errno = 13)

我已经在清单文件中设置了权限，并使用以下代码获得运行时权限

List<Permissions> permissions = await Permission.getPermissionStatus([PermissionName.Storage]);
permissions.forEach((p) async {
  if(p.permissionStatus != PermissionStatus.allow){
    final res = await Permission.requestSinglePermission(PermissionName.Storage);
    print(res);
  }
});

我已经在设置中验证了该应用程序已获得许可，也正如此处某些答案所建议的那样，我还尝试手动授予设置应用程序的许可，但没有用。

Answer 1

下面的代码在我的应用程序中运行良好，可以使用 url 将图像下载到外部存储

Future<bool> downloadImage(String url) async {
  await new Future.delayed(new Duration(seconds: 1));
  bool checkResult =
      await SimplePermissions.checkPermission(Permission.WriteExternalStorage);
  if (!checkResult) {
    var status = await SimplePermissions.requestPermission(
        Permission.WriteExternalStorage);
    if (status == PermissionStatus.authorized) {
      var res = await saveImage(url);
      return res != null;
    }
  } else {
    var res = await saveImage(url);
    return res != null;
  }
  return false;
}

Future<Io.File> saveImage(String url) async {
  try {
    final file = await getImageFromNetwork(url);
    var dir = await getExternalStorageDirectory();
    var testdir =
        await new Io.Directory('${dir.path}/iLearn').create(recursive: true);
    IM.Image image = IM.decodeImage(file.readAsBytesSync());
    return new Io.File(
        '${testdir.path}/${DateTime.now().toUtc().toIso8601String()}.png')
      ..writeAsBytesSync(IM.encodePng(image));
  } catch (e) {
    print(e);
    return null;
  }
}

  Future<Io.File> getImageFromNetwork(String url) async {
  var cacheManager = await CacheManager.getInstance();
  Io.File file = await cacheManager.getFile(url);
  return file;
}

命名空间

import 'dart:io' as Io;
import 'package:image/image.dart' as IM;
import 'package:flutter_cache_manager/flutter_cache_manager.dart';
import 'package:path_provider/path_provider.dart';
import 'package:simple_permissions/simple_permissions.dart';

希望能帮助到你

Answer 2

您需要在使用 getExternalStorageDirectory 保存文件之前请求权限。

将此添加到 Androidmanifest.xml：

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

然后使用permission_handler包获取Storage权限：

https://pub.dev/packages/permission_handler

如果您在模拟器中运行，则 getExternalStorageDirectory 返回：

/storage/emulated/0/Android/data/com.example.myapp/files/

如果您只需要外部目录在其下创建目录，则只需使用：

/storage/emulated/0/

您可以在此文件夹下创建一个目录，以便他们的用户可以打开文件。

Answer 3

对于 Android 11 及更高版本，android 更改其策略，以便您在 AndroidManifest.. 中添加权限。

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

并且还在 <application ......

android:requestLegacyExternalStorage="true"
android:preserveLegacyExternalStorage="true"

Answer 4

这是一个可操作的 100% Dart 代码，使事情变得更容易：

import 'dart:async';
import 'dart:developer';
import 'dart:io';

import 'package:path/path.dart' as Path;
import 'package:path_provider/path_provider.dart';

///getExternalStoragePublicDirectory
enum extPublicDir {
  Music,
  PodCasts,
  Ringtones,
  Alarms,
  Notifications,
  Pictures,
  Movies,
  Download,
  DCIM,
  Documents,
  Screenshots,
  Audiobooks,
}
/// use in loop or without:
/// generation loop of a creation of the same directory in a list
/// public or shared folders by the Android system
/*
 for (var ext in extPublicDir.values) {

   ExtStorage.createFolderInPublicDir(
     type: ext,  //or without loop : extPublicDir.Download,
     folderName: "folderName",  // folder or folder/subFolder/... to create
   );

 }
*/
/// provided the ability to create folders and files within folders
/// public or shared from the Android system
///
/// /storage/emulated/0/Audiobooks
/// /storage/emulated/0/PodCasts
/// /storage/emulated/0/Ringtones
/// /storage/emulated/0/Alarms
/// /storage/emulated/0/Notifications
/// /storage/emulated/0/Pictures
/// /storage/emulated/0/Movies
/// storage/emulated/0/Download
/// /storage/emulated/0/DCIM
/// /storage/emulated/0/Documents
/// /storage/emulated/0/Screenshots  //Screenshots dropping ?
/// /storage/emulated/0/Music/

class ExtStorage {

  //According to path_provider
  static Future<String> get _directoryPathESD async {
    var directory = await getExternalStorageDirectory();
    if (directory != null) {
      log('directory:${directory.path}');

      return directory.path;
    }
    log('_directoryPathESD==null');

    return '';
  }

  /// create or not, but above all returns the created folder in a public folder
  /// official, folderName = '', only return the public folder: useful for
  /// manage a file at its root
  static Future<String> createFolderInPublicDir({
    required extPublicDir type,
    required String folderName,
  }) async {

    var _appDocDir = await _directoryPathESD;

    log("createFolderInPublicDir:_appDocDir:${_appDocDir.toString()}");

    var values = _appDocDir.split("${Platform.pathSeparator}");
    values.forEach(print);

    var dim = values.length - 4; // Android/Data/package.name/files
    _appDocDir = "";

    for (var i = 0; i < dim; i++) {
      _appDocDir += values[i];
      _appDocDir += "${Platform.pathSeparator}";
    }
    _appDocDir += "${type.toString().split('.').last}${Platform.pathSeparator}";
    _appDocDir += folderName;

    log("createFolderInPublicDir:_appDocDir:$_appDocDir");

    if (await Directory(_appDocDir).exists()) {
      log("createFolderInPublicDir:reTaken:$_appDocDir");

      return _appDocDir;
    } else {
      log("createFolderInPublicDir:toCreate:$_appDocDir");
      //if folder not exists create folder and then return its path
      final _appDocDirNewFolder =
          await Directory(_appDocDir).create(recursive: true);
      final pathNorma = Path.normalize(_appDocDirNewFolder.path);
      log("createFolderInPublicDir:ToCreate:pathNorma:$pathNorma");

      return pathNorma;
    }
  }
}