[path_provider] Fix93198: Added getDownloadsDirectory() for Android (flutter#4708)

This PR adds the Android implementation for the getDownloadsDirectory() function by making getDownloadsDirectory redirect at the Dart level to getExternalStorageDirectories with the downloads directory constant.

*List which issues are fixed by this PR. You must list at least one issue.*
Fixes [flutter#93198](flutter#93198)

Author: talhakhan1297

packages/path_provider/path_provider_android/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 2.2.0
+
+* Adds implementation of `getDownloadsDirectory()`.
+
 ## 2.1.1
 
 * Adds pub topics to package metadata.

packages/path_provider/path_provider_android/example/lib/main.dart

@@ -41,6 +41,7 @@ class _MyHomePageState extends State<MyHomePage> {
   Future<String?>? _appDocumentsDirectory;
   Future<String?>? _appCacheDirectory;
   Future<String?>? _externalDocumentsDirectory;
+  Future<String?>? _externalDownloadsDirectory;
   Future<List<String>?>? _externalStorageDirectories;
   Future<List<String>?>? _externalCacheDirectories;
 
@@ -118,6 +119,12 @@ class _MyHomePageState extends State<MyHomePage> {
     });
   }
 
+  void _requestDownloadsDirectory() {
+    setState(() {
+      _externalDownloadsDirectory = provider.getDownloadsPath();
+    });
+  }
+
   @override
   Widget build(BuildContext context) {
     return Scaffold(
@@ -199,6 +206,15 @@ class _MyHomePageState extends State<MyHomePage> {
             ]),
             FutureBuilder<List<String>?>(
                 future: _externalCacheDirectories, builder: _buildDirectories),
+            Padding(
+              padding: const EdgeInsets.all(16.0),
+              child: ElevatedButton(
+                onPressed: _requestDownloadsDirectory,
+                child: const Text('Get Downloads Directory'),
+              ),
+            ),
+            FutureBuilder<String?>(
+                future: _externalDownloadsDirectory, builder: _buildDirectory),
           ],
         ),
       ),

packages/path_provider/path_provider_android/lib/path_provider_android.dart

@@ -81,12 +81,20 @@ class PathProviderAndroid extends PathProviderPlatform {
   Future<List<String>?> getExternalStoragePaths({
     StorageDirectory? type,
   }) async {
-    return (await _api.getExternalStoragePaths(_convertStorageDirectory(type)))
-        .cast<String>();
+    return _getExternalStoragePaths(type: type);
   }
 
   @override
-  Future<String?> getDownloadsPath() {
-    throw UnsupportedError('getDownloadsPath is not supported on Android');
+  Future<String?> getDownloadsPath() async {
+    final List<String> paths =
+        await _getExternalStoragePaths(type: StorageDirectory.downloads);
+    return paths.isEmpty ? null : paths.first;
+  }
+
+  Future<List<String>> _getExternalStoragePaths({
+    StorageDirectory? type,
+  }) async {
+    return (await _api.getExternalStoragePaths(_convertStorageDirectory(type)))
+        .cast<String>();
   }
 }

packages/path_provider/path_provider_android/pubspec.yaml

@@ -2,7 +2,7 @@ name: path_provider_android
 description: Android implementation of the path_provider plugin.
 repository: https://github.com/flutter/packages/tree/main/packages/path_provider/path_provider_android
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+path_provider%22
-version: 2.1.1
+version: 2.2.0
 
 environment:
   sdk: ">=2.19.0 <4.0.0"

packages/path_provider/path_provider_android/test/path_provider_android_test.dart

@@ -18,6 +18,10 @@ const String kExternalStoragePaths = 'externalStoragePaths';
 const String kDownloadsPath = 'downloadsPath';
 
 class _Api implements TestPathProviderApi {
+  _Api({this.returnsExternalStoragePaths = true});
+
+  final bool returnsExternalStoragePaths;
+
   @override
   String? getApplicationDocumentsPath() => kApplicationDocumentsPath;
 
@@ -34,8 +38,9 @@ class _Api implements TestPathProviderApi {
   String? getExternalStoragePath() => kExternalStoragePaths;
 
   @override
-  List<String?> getExternalStoragePaths(messages.StorageDirectory directory) =>
-      <String>[kExternalStoragePaths];
+  List<String?> getExternalStoragePaths(messages.StorageDirectory directory) {
+    return <String?>[if (returnsExternalStoragePaths) kExternalStoragePaths];
+  }
 
   @override
   String? getTemporaryPath() => kTemporaryPath;
@@ -98,13 +103,18 @@ void main() {
       });
     } // end of for-loop
 
-    test('getDownloadsPath fails', () async {
-      try {
-        await pathProvider.getDownloadsPath();
-        fail('should throw UnsupportedError');
-      } catch (e) {
-        expect(e, isUnsupportedError);
-      }
+    test('getDownloadsPath succeeds', () async {
+      final String? path = await pathProvider.getDownloadsPath();
+      expect(path, kExternalStoragePaths);
+    });
+
+    test(
+        'getDownloadsPath returns null, when getExternalStoragePaths returns '
+        'an empty list', () async {
+      final PathProviderAndroid pathProvider = PathProviderAndroid();
+      TestPathProviderApi.setup(_Api(returnsExternalStoragePaths: false));
+      final String? path = await pathProvider.getDownloadsPath();
+      expect(path, null);
     });
   });
 }