Use the storage access framework

Everything related to file system access has been rewritten to make use
of the storage access framework. This means that the
WRITE_EXTERNAL_STORAGE is no longer needed. Because of that, the
dependency on permission_handler could be dropped and all code related
to permission handling has been removed. To be able to open a whole
document tree, the minSdkVersion was bumped to 21. Finally the file
selector was rewritten using custom platform dependent code.

android/app/build.gradle

@@ -38,7 +38,7 @@ android {
 
     defaultConfig {
         applicationId "de.johrpan.musicus"
-        minSdkVersion 16
+        minSdkVersion 21
         targetSdkVersion 29
         versionCode flutterVersionCode.toInteger()
         versionName flutterVersionName

android/app/src/main/AndroidManifest.xml

@@ -1,8 +1,6 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
     package="de.johrpan.musicus">
 
-    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
-
     <application
         android:name="io.flutter.app.FlutterApplication"
         android:label="Musicus"

android/app/src/main/kotlin/de/johrpan/musicus/MainActivity.kt

@@ -1,39 +1,117 @@
 package de.johrpan.musicus
 
-import androidx.annotation.NonNull;
+import android.app.Activity
-import androidx.core.content.ContextCompat
+import android.content.Intent
+import android.net.Uri
+import android.provider.DocumentsContract
+import androidx.annotation.NonNull
 import io.flutter.embedding.android.FlutterActivity
 import io.flutter.embedding.engine.FlutterEngine
 import io.flutter.plugin.common.MethodChannel
 import io.flutter.plugins.GeneratedPluginRegistrant
 
+class Document(private val id: String, private val name: String, private val parentId: String?, private val isDirectory: Boolean) {
+    fun toMap(): Map<String, Any?> {
+        return mapOf(
+                "id" to id,
+                "name" to name,
+                "parentId" to parentId,
+                "isDirectory" to isDirectory
+        )
+    }
+}
+
 class MainActivity : FlutterActivity() {
     private val CHANNEL = "de.johrpan.musicus/platform"
+    private val AODT_REQUEST = 0
+
+    private var aodtResult: MethodChannel.Result? = null
 
     override fun configureFlutterEngine(@NonNull flutterEngine: FlutterEngine) {
         GeneratedPluginRegistrant.registerWith(flutterEngine)
 
         MethodChannel(flutterEngine.dartExecutor.binaryMessenger, CHANNEL).setMethodCallHandler { call, result ->
-            if (call.method == "getStorageRoots") {
+            if (call.method == "openTree") {
-                result.success(getStorageRoots())
+                aodtResult = result
+                // We will get the result within onActivityResult
+                openTree()
+            } else if (call.method == "getChildren") {
+                val treeUri = Uri.parse(call.argument<String>("treeUri"))
+                val parentId = call.argument<String>("parentId")
+                val children = getChildren(treeUri, parentId)
+                result.success(children.map { it.toMap() })
             } else {
                 result.notImplemented()
             }
         }
     }
 
-    private fun getStorageRoots(): ArrayList<String> {
+    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
-        val result = ArrayList<String>()
+        super.onActivityResult(requestCode, resultCode, data)
 
-        ContextCompat.getExternalFilesDirs(this, null).forEach {
+        if (requestCode == AODT_REQUEST) {
-            val path = it.absolutePath;
+            if (resultCode == Activity.RESULT_OK && data?.data != null) {
-            val index = path.lastIndexOf("/Android/data/")
+                // Drop all old URIs
+                contentResolver.persistedUriPermissions.forEach {
+                    contentResolver.releasePersistableUriPermission(it.uri, Intent.FLAG_GRANT_WRITE_URI_PERMISSION)
+                }
 
-            if (index > 0) {
+                // We already checked for null
-                result.add(path.substring(0, index))
+                val uri = data.data!!
+                contentResolver.takePersistableUriPermission(uri, Intent.FLAG_GRANT_WRITE_URI_PERMISSION)
+
+                aodtResult?.success(uri.toString())
+            } else {
+                aodtResult?.success(null)
             }
         }
+    }
 
-        return result
+    /**
+     * Open a document tree using the storage access framework
+     *
+     * The result is handled within [onActivityResult]
+     */
+    private fun openTree() {
+        val intent = Intent(Intent.ACTION_OPEN_DOCUMENT_TREE)
+        intent.addFlags(Intent.FLAG_GRANT_WRITE_URI_PERMISSION)
+        intent.addFlags(Intent.FLAG_GRANT_PERSISTABLE_URI_PERMISSION)
+
+        startActivityForResult(intent, AODT_REQUEST)
+    }
+
+    /**
+     * List children of a directory
+     *
+     * @param treeUri The treeUri from the ACTION_OPEN_DOCUMENT_TREE request
+     * @param parentId Document ID of the parent directory or null for the top level directory
+     * @return List of directories and files within the directory
+     */
+    private fun getChildren(treeUri: Uri, parentId: String?): List<Document> {
+        val realParentId = parentId ?: DocumentsContract.getTreeDocumentId(treeUri)
+        val children = ArrayList<Document>()
+        val childrenUri = DocumentsContract.buildChildDocumentsUriUsingTree(treeUri, realParentId)
+
+        val cursor = contentResolver.query(
+                childrenUri,
+                arrayOf(DocumentsContract.Document.COLUMN_DOCUMENT_ID,
+                        DocumentsContract.Document.COLUMN_DISPLAY_NAME,
+                        DocumentsContract.Document.COLUMN_MIME_TYPE),
+                null, null, null)
+
+        if (cursor != null) {
+            while (cursor.moveToNext()) {
+                val id = cursor.getString(0)
+                val name = cursor.getString(1)
+                val isDirectory = cursor.getString(2) == DocumentsContract.Document.MIME_TYPE_DIR
+
+                // Use parentId here to let the consumer know that we are at the top level.
+                children.add(Document(id, name, parentId, isDirectory))
+            }
+
+            cursor.close()
+        }
+
+        return children
     }
 }

lib/app.dart

@@ -4,7 +4,6 @@ import 'package:flutter/material.dart';
 
 import 'backend.dart';
 import 'screens/home.dart';
-import 'selectors/files.dart';
 import 'widgets/player_bar.dart';
 
 class App extends StatelessWidget {
@@ -34,37 +33,6 @@ class App extends StatelessWidget {
             return Material(
               color: Theme.of(context).scaffoldBackgroundColor,
             );
-          } else if (backend.status == BackendStatus.needsPermissions) {
-            return Material(
-              color: Theme.of(context).scaffoldBackgroundColor,
-              child: Column(
-                mainAxisAlignment: MainAxisAlignment.center,
-                children: <Widget>[
-                  Text(
-                    'Musicus needs permissions\nto access your files.',
-                    textAlign: TextAlign.center,
-                    style: Theme.of(context).textTheme.headline6,
-                  ),
-                  SizedBox(
-                    height: 16.0,
-                  ),
-                  ListTile(
-                    leading: const Icon(Icons.done),
-                    title: Text('Grant permissions'),
-                    onTap: () {
-                      backend.requestPermissions();
-                    },
-                  ),
-                  ListTile(
-                    leading: const Icon(Icons.settings),
-                    title: Text('Open system\'s app settings'),
-                    onTap: () {
-                      backend.openAppSettings();
-                    },
-                  ),
-                ],
-              ),
-            );
           } else if (backend.status == BackendStatus.setup) {
             return Material(
               color: Theme.of(context).scaffoldBackgroundColor,
@@ -82,20 +50,8 @@ class App extends StatelessWidget {
                   ListTile(
                     leading: const Icon(Icons.folder_open),
                     title: Text('Choose path'),
-                    onTap: () async {
+                    onTap: () {
-                      final path = await Navigator.push<String>(
+                      backend.chooseMusicLibraryUri();
-                        context,
-                        MaterialPageRoute(
-                          builder: (context) => FilesSelector(
-                            mode: FilesSelectorMode.directory,
-                          ),
-                          fullscreenDialog: true,
-                        ),
-                      );
-
-                      if (path != null) {
-                        backend.setMusicLibraryPath(path);
-                      }
                     },
                   ),
                 ],

lib/backend.dart

@@ -1,5 +1,5 @@
+import 'package:flutter/services.dart';
 import 'package:flutter/widgets.dart';
-import 'package:permission_handler/permission_handler.dart';
 import 'package:rxdart/rxdart.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 
@@ -7,7 +7,6 @@ import 'database.dart';
 
 enum BackendStatus {
   loading,
-  needsPermissions,
   setup,
   ready,
 }
@@ -27,15 +26,15 @@ class Backend extends StatefulWidget {
 }
 
 class BackendState extends State<Backend> {
-  final _permissionHandler = PermissionHandler();
+  static const _platform = MethodChannel('de.johrpan.musicus/platform');
 
   final playerActive = BehaviorSubject.seeded(false);
   final playing = BehaviorSubject.seeded(false);
   final position = BehaviorSubject.seeded(0.0);
 
-  Database db;
   BackendStatus status = BackendStatus.loading;
-  String musicLibraryPath;
+  Database db;
+  String musicLibraryUri;
 
   SharedPreferences _shPref;
 
@@ -54,25 +53,15 @@ class BackendState extends State<Backend> {
   }
 
   Future<void> _load() async {
-    _shPref = await SharedPreferences.getInstance();
-    musicLibraryPath = _shPref.getString('musicLibraryPath');
-
     db = Database('musicus.sqlite');
+    _shPref = await SharedPreferences.getInstance();
+    musicLibraryUri = _shPref.getString('musicLibraryUri');
     
-    final permissionStatus =
+    _loadMusicLibrary();
-        await _permissionHandler.checkPermissionStatus(PermissionGroup.storage);
-
-    if (permissionStatus != PermissionStatus.granted) {
-      setState(() {
-        status = BackendStatus.needsPermissions;
-      });
-    } else {
-      await _loadMusicLibrary();
-    }
   }
 
   Future<void> _loadMusicLibrary() async {
-    if (musicLibraryPath == null) {
+    if (musicLibraryUri == null) {
       setState(() {
         status = BackendStatus.setup;
       });
@@ -83,26 +72,19 @@ class BackendState extends State<Backend> {
     }
   }
 
-  Future<void> requestPermissions() async {
+  Future<void> chooseMusicLibraryUri() async {
-    final result =
+    final uri = await _platform.invokeMethod<String>('openTree');
-        await _permissionHandler.requestPermissions([PermissionGroup.storage]);
 
-    if (result[PermissionGroup.storage] == PermissionStatus.granted) {
+    if (uri != null) {
-      _loadMusicLibrary();
+      musicLibraryUri = uri;
+      await _shPref.setString('musicLibraryUri', uri);
+      setState(() {
+        status = BackendStatus.loading;
+      });
+      await _loadMusicLibrary();
     }
   }
 
-  Future<void> openAppSettings() => _permissionHandler.openAppSettings();
-
-  Future<void> setMusicLibraryPath(String path) async {
-    musicLibraryPath = path;
-    await _shPref.setString('musicLibraryPath', path);
-    setState(() {
-      status = BackendStatus.loading;
-    });
-    await _loadMusicLibrary();
-  }
-
   void startPlayer() {
     playerActive.add(true);
   }

lib/editors/tracks.dart

@@ -1,5 +1,4 @@
 import 'package:flutter/material.dart';
-import 'package:path/path.dart' as p;
 
 import '../backend.dart';
 import '../database.dart';
@@ -7,6 +6,7 @@ import '../selectors/files.dart';
 import '../selectors/recording.dart';
 import '../widgets/recording_tile.dart';
 
+// TODO: Update for storage access framework.
 class TrackModel {
   String path;
 
@@ -58,22 +58,9 @@ class _TracksEditorState extends State<TracksEditor> {
                   final Set<String> paths = await Navigator.push(
                     context,
                     MaterialPageRoute(
-                      builder: (context) => FilesSelector(
+                      builder: (context) => FilesSelector(),
-                        baseDirectory: backend.musicLibraryPath,
-                      ),
                     ),
                   );
-
-                  if (paths != null) {
-                    setState(() {
-                      for (final path in paths) {
-                        tracks.add(TrackModel(p.relative(
-                          path,
-                          from: backend.musicLibraryPath,
-                        )));
-                      }
-                    });
-                  }
                 },
               ),
             ),

lib/screens/settings.dart

@@ -1,7 +1,6 @@
 import 'package:flutter/material.dart';
 
 import '../backend.dart';
-import '../selectors/files.dart';
 
 class SettingsScreen extends StatelessWidget {
   @override
@@ -17,21 +16,9 @@ class SettingsScreen extends StatelessWidget {
           ListTile(
             leading: Icon(Icons.library_music),
             title: Text('Music library path'),
-            subtitle: Text(backend.musicLibraryPath),
+            subtitle: Text(backend.musicLibraryUri),
-            onTap: () async {
+            onTap: () {
-              final path = await Navigator.push<String>(
+              backend.chooseMusicLibraryUri();
-                context,
-                MaterialPageRoute(
-                  builder: (context) => FilesSelector(
-                    mode: FilesSelectorMode.directory,
-                  ),
-                  fullscreenDialog: true,
-                ),
-              );
-
-              if (path != null) {
-                backend.setMusicLibraryPath(path);
-              }
             },
           ),
         ],

lib/selectors/files.dart

@@ -1,23 +1,22 @@
-import 'dart:io';
-
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
-import 'package:path/path.dart' as path;
 
-enum FilesSelectorMode {
+import '../backend.dart';
-  files,
+
-  directory,
+class Document {
+  final String id;
+  final String name;
+  final String parent;
+  final bool isDirectory;
+
+  Document.fromMap(Map<dynamic, dynamic> map)
+      : id = map['id'],
+        name = map['name'],
+        parent = map['parent'],
+        isDirectory = map['isDirectory'];
 }
 
 class FilesSelector extends StatefulWidget {
-  final FilesSelectorMode mode;
-  final String baseDirectory;
-
-  FilesSelector({
-    this.mode = FilesSelectorMode.files,
-    this.baseDirectory,
-  });
-
   @override
   _FilesSelectorState createState() => _FilesSelectorState();
 }
@@ -25,104 +24,21 @@ class FilesSelector extends StatefulWidget {
 class _FilesSelectorState extends State<FilesSelector> {
   static const platform = MethodChannel('de.johrpan.musicus/platform');
 
-  Directory baseDirectory;
+  BackendState backend;
-  List<Directory> storageRoots;
+  List<Document> history = [];
-  List<Directory> directories = [];
+  List<Document> children = [];
-  List<FileSystemEntity> contents = [];
+  Set<String> selectedIds = {};
-  Set<String> selectedPaths = {};
 
   @override
-  void initState() {
+  void didChangeDependencies() {
-    super.initState();
+    super.didChangeDependencies();
 
-    if (widget.baseDirectory == null) {
+    backend = Backend.of(context);
-      platform.invokeListMethod<String>('getStorageRoots').then((sr) {
+    loadChildren();
-        setState(() {
-          storageRoots = sr.map((path) => Directory(path)).toList();
-        });
-      });
-    } else {
-      baseDirectory = Directory(widget.baseDirectory);
-      openDirectory(baseDirectory);
-    }
   }
 
   @override
   Widget build(BuildContext context) {
-    String titleText;
-    Widget body;
-
-    if (directories.isEmpty && storageRoots != null) {
-      titleText = 'Storage devices';
-      body = ListView(
-        children: storageRoots
-            .map((dir) => ListTile(
-                  leading: const Icon(Icons.storage),
-                  title: Text(dir.path),
-                  onTap: () {
-                    setState(() {
-                      directories.add(dir);
-                    });
-
-                    openDirectory(dir);
-                  },
-                ))
-            .toList(),
-      );
-    } else if (contents != null) {
-      if (directories.isEmpty) {
-        titleText = 'Base directory';
-      } else {
-        titleText = path.basename(directories.last.path);
-      }
-
-      body = ListView(
-        children: contents.map((fse) {
-          Widget result;
-
-          if (fse is Directory) {
-            result = ListTile(
-              leading: const Icon(Icons.folder),
-              title: Text(path.basename(fse.path)),
-              onTap: () {
-                setState(() {
-                  directories.add(fse);
-                });
-
-                openDirectory(fse);
-              },
-            );
-          } else if (fse is File) {
-            if (widget.mode == FilesSelectorMode.files) {
-              result = CheckboxListTile(
-                value: selectedPaths.contains(fse.path),
-                secondary: Icon(Icons.insert_drive_file),
-                title: Text(path.basename(fse.path)),
-                onChanged: (selected) {
-                  setState(() {
-                    if (selected) {
-                      selectedPaths.add(fse.path);
-                    } else {
-                      selectedPaths.remove(fse.path);
-                    }
-                  });
-                },
-              );
-            } else {
-              result = ListTile(
-                leading: const Icon(Icons.insert_drive_file),
-                title: Text(path.basename(fse.path)),
-              );
-            }
-          }
-
-          return result;
-        }).toList(),
-      );
-    } else {
-      body = Container();
-    }
-
     return WillPopScope(
       child: Scaffold(
         appBar: AppBar(
@@ -135,14 +51,9 @@ class _FilesSelectorState extends State<FilesSelector> {
           ),
           actions: <Widget>[
             FlatButton(
-              child: Text(
+              child: Text('DONE'),
-                  widget.mode == FilesSelectorMode.files ? 'DONE' : 'SELECT'),
               onPressed: () {
-                Navigator.pop(
+                Navigator.pop(context, selectedIds);
-                    context,
-                    widget.mode == FilesSelectorMode.files
-                        ? selectedPaths
-                        : directories.last?.path);
               },
             ),
           ],
@@ -152,71 +63,96 @@ class _FilesSelectorState extends State<FilesSelector> {
             Material(
               elevation: 2.0,
               child: ListTile(
-                leading: directories.isNotEmpty
+                leading: IconButton(
-                    ? IconButton(
+                  icon: const Icon(Icons.arrow_upward),
-                        icon: const Icon(Icons.arrow_upward),
+                  onPressed: history.isNotEmpty ? up : null,
-                        onPressed: up,
+                ),
-                      )
+                title: Text(
-                    : null,
+                    history.isNotEmpty ? history.last.name : 'Music library'),
-                title: Text(titleText),
               ),
             ),
             Expanded(
-              child: body,
+              child: ListView.builder(
+                itemCount: children.length,
+                itemBuilder: (context, index) {
+                  final document = children[index];
+
+                  if (document.isDirectory) {
+                    return ListTile(
+                      leading: const Icon(Icons.folder),
+                      title: Text(document.name),
+                      onTap: () {
+                        setState(() {
+                          history.add(document);
+                        });
+                        loadChildren();
+                      },
+                    );
+                  } else {
+                    return CheckboxListTile(
+                      controlAffinity: ListTileControlAffinity.trailing,
+                      secondary: const Icon(Icons.insert_drive_file),
+                      title: Text(document.name),
+                      value: selectedIds.contains(document.id),
+                      onChanged: (selected) {
+                        setState(() {
+                          if (selected) {
+                            selectedIds.add(document.id);
+                          } else {
+                            selectedIds.remove(document.id);
+                          }
+                        });
+                      },
+                    );
+                  }
+                },
+              ),
             ),
           ],
         ),
       ),
-      onWillPop: () {
+      onWillPop: () => Future.value(up()),
-        if (directories.isNotEmpty) {
-          up();
-          return Future.value(false);
-        } else {
-          return Future.value(true);
-        }
-      },
     );
   }
 
-  Future<void> openDirectory(Directory directory) async {
+  Future<void> loadChildren() async {
     setState(() {
-      contents.clear();
+      children = [];
     });
 
-    final fses = await directory.list().toList();
+    final childrenMaps = await platform.invokeListMethod<Map<dynamic, dynamic>>(
-    fses.sort((fse1, fse2) {
+      'getChildren',
-      int compareBasenames() =>
+      {
-          path.basename(fse1.path).compareTo(path.basename(fse2.path));
+        'treeUri': backend.musicLibraryUri,
+        'parentId': history.isNotEmpty ? history.last.id : null,
+      },
+    );
 
-      if (fse1 is Directory) {
+    final newChildren = childrenMaps.map((m) => Document.fromMap(m)).toList();
-        if (fse2 is Directory) {
+    newChildren.sort((d1, d2) {
-          return compareBasenames();
+      if (d1.isDirectory != d2.isDirectory) {
-        } else {
+        return d1.isDirectory ? -1 : 1;
-          return -1;
-        }
-      } else if (fse2 is Directory) {
-        return 1;
       } else {
-        return compareBasenames();
+        return d1.name.compareTo(d2.name);
       }
     });
 
     setState(() {
-      contents = fses;
+      children = newChildren;
     });
   }
 
-  void up() {
+  bool up() {
-    if (directories.isNotEmpty) {
+    if (history.isNotEmpty) {
       setState(() {
-        directories.removeLast();
+        history.removeLast();
       });
 
-      if (directories.isNotEmpty) {
+      loadChildren();
-        openDirectory(directories.last);
+
-      } else if (baseDirectory != null) {
+      return false;
-        openDirectory(baseDirectory);
+    } else {
-      }
+      return true;
     }
   }
 }

pubspec.yaml

@@ -13,7 +13,6 @@ dependencies:
     sdk: flutter
   moor_flutter:
   path:
-  permission_handler:
   rxdart:
   shared_preferences: