[path_provider] Migrate examples to null-safety (#3559)

Allows running the examples in strong mode, even though the integration tests can't yet be.

Converts the macOS example to use the platform interface, rather than the app-facing package, to eliminate the circular dependency. Also does some cleanup and simplification of the desktop example pubspecs.

Does not update versions/changelogs since this won't be explicitly published, given that it's example-only.

Author: stuartmorgan-g

packages/path_provider/path_provider/example/integration_test/path_provider_test.dart

@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import 'dart:async';
 
 import 'dart:io';

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

@@ -28,21 +28,21 @@ class MyApp extends StatelessWidget {
 }
 
 class MyHomePage extends StatefulWidget {
-  MyHomePage({Key key, this.title}) : super(key: key);
+  MyHomePage({Key? key, required this.title}) : super(key: key);
   final String title;
 
   @override
   _MyHomePageState createState() => _MyHomePageState();
 }
 
 class _MyHomePageState extends State<MyHomePage> {
-  Future<Directory> _tempDirectory;
-  Future<Directory> _appSupportDirectory;
-  Future<Directory> _appLibraryDirectory;
-  Future<Directory> _appDocumentsDirectory;
-  Future<Directory> _externalDocumentsDirectory;
-  Future<List<Directory>> _externalStorageDirectories;
-  Future<List<Directory>> _externalCacheDirectories;
+  Future<Directory?>? _tempDirectory;
+  Future<Directory?>? _appSupportDirectory;
+  Future<Directory?>? _appLibraryDirectory;
+  Future<Directory?>? _appDocumentsDirectory;
+  Future<Directory?>? _externalDocumentsDirectory;
+  Future<List<Directory>?>? _externalStorageDirectories;
+  Future<List<Directory>?>? _externalCacheDirectories;
 
   void _requestTempDirectory() {
     setState(() {
@@ -51,13 +51,13 @@ class _MyHomePageState extends State<MyHomePage> {
   }
 
   Widget _buildDirectory(
-      BuildContext context, AsyncSnapshot<Directory> snapshot) {
+      BuildContext context, AsyncSnapshot<Directory?> snapshot) {
     Text text = const Text('');
     if (snapshot.connectionState == ConnectionState.done) {
       if (snapshot.hasError) {
         text = Text('Error: ${snapshot.error}');
       } else if (snapshot.hasData) {
-        text = Text('path: ${snapshot.data.path}');
+        text = Text('path: ${snapshot.data!.path}');
       } else {
         text = const Text('path unavailable');
       }
@@ -66,14 +66,14 @@ class _MyHomePageState extends State<MyHomePage> {
   }
 
   Widget _buildDirectories(
-      BuildContext context, AsyncSnapshot<List<Directory>> snapshot) {
+      BuildContext context, AsyncSnapshot<List<Directory>?> snapshot) {
     Text text = const Text('');
     if (snapshot.connectionState == ConnectionState.done) {
       if (snapshot.hasError) {
         text = Text('Error: ${snapshot.error}');
       } else if (snapshot.hasData) {
         final String combined =
-            snapshot.data.map((Directory d) => d.path).join(', ');
+            snapshot.data!.map((Directory d) => d.path).join(', ');
         text = Text('paths: $combined');
       } else {
         text = const Text('path unavailable');
@@ -134,7 +134,7 @@ class _MyHomePageState extends State<MyHomePage> {
                 onPressed: _requestTempDirectory,
               ),
             ),
-            FutureBuilder<Directory>(
+            FutureBuilder<Directory?>(
                 future: _tempDirectory, builder: _buildDirectory),
             Padding(
               padding: const EdgeInsets.all(16.0),
@@ -143,7 +143,7 @@ class _MyHomePageState extends State<MyHomePage> {
                 onPressed: _requestAppDocumentsDirectory,
               ),
             ),
-            FutureBuilder<Directory>(
+            FutureBuilder<Directory?>(
                 future: _appDocumentsDirectory, builder: _buildDirectory),
             Padding(
               padding: const EdgeInsets.all(16.0),
@@ -152,7 +152,7 @@ class _MyHomePageState extends State<MyHomePage> {
                 onPressed: _requestAppSupportDirectory,
               ),
             ),
-            FutureBuilder<Directory>(
+            FutureBuilder<Directory?>(
                 future: _appSupportDirectory, builder: _buildDirectory),
             Padding(
               padding: const EdgeInsets.all(16.0),
@@ -161,7 +161,7 @@ class _MyHomePageState extends State<MyHomePage> {
                 onPressed: _requestAppLibraryDirectory,
               ),
             ),
-            FutureBuilder<Directory>(
+            FutureBuilder<Directory?>(
                 future: _appLibraryDirectory, builder: _buildDirectory),
             Padding(
               padding: const EdgeInsets.all(16.0),
@@ -172,7 +172,7 @@ class _MyHomePageState extends State<MyHomePage> {
                     Platform.isIOS ? null : _requestExternalStorageDirectory,
               ),
             ),
-            FutureBuilder<Directory>(
+            FutureBuilder<Directory?>(
                 future: _externalDocumentsDirectory, builder: _buildDirectory),
             Column(children: <Widget>[
               Padding(
@@ -190,7 +190,7 @@ class _MyHomePageState extends State<MyHomePage> {
                 ),
               ),
             ]),
-            FutureBuilder<List<Directory>>(
+            FutureBuilder<List<Directory>?>(
                 future: _externalStorageDirectories,
                 builder: _buildDirectories),
             Column(children: <Widget>[
@@ -204,7 +204,7 @@ class _MyHomePageState extends State<MyHomePage> {
                 ),
               ),
             ]),
-            FutureBuilder<List<Directory>>(
+            FutureBuilder<List<Directory>?>(
                 future: _externalCacheDirectories, builder: _buildDirectories),
           ],
         ),

packages/path_provider/path_provider/example/pubspec.yaml

@@ -23,5 +23,5 @@ flutter:
   uses-material-design: true
 
 environment:
-  sdk: ">=2.1.0 <3.0.0"
+  sdk: ">=2.12.0-0 <3.0.0"
   flutter: ">=1.12.13+hotfix.5"

packages/path_provider/path_provider/example/test_driver/integration_test.dart

@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';

packages/path_provider/path_provider_linux/example/integration_test/path_provider_test.dart

@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import 'dart:io';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:path_provider_linux/path_provider_linux.dart';

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

@@ -4,7 +4,7 @@ import 'dart:async';
 import 'package:flutter/services.dart';
 import 'package:path_provider_linux/path_provider_linux.dart';
 
-void main() async {
+void main() {
   runApp(MyApp());
 }
 
@@ -15,10 +15,10 @@ class MyApp extends StatefulWidget {
 }
 
 class _MyAppState extends State<MyApp> {
-  String _tempDirectory = 'Unknown';
-  String _downloadsDirectory = 'Unknown';
-  String _appSupportDirectory = 'Unknown';
-  String _documentsDirectory = 'Unknown';
+  String? _tempDirectory = 'Unknown';
+  String? _downloadsDirectory = 'Unknown';
+  String? _appSupportDirectory = 'Unknown';
+  String? _documentsDirectory = 'Unknown';
   final PathProviderLinux _provider = PathProviderLinux();
 
   @override
@@ -29,10 +29,10 @@ class _MyAppState extends State<MyApp> {
 
   // Platform messages are asynchronous, so we initialize in an async method.
   Future<void> initDirectories() async {
-    String tempDirectory;
-    String downloadsDirectory;
-    String appSupportDirectory;
-    String documentsDirectory;
+    String? tempDirectory;
+    String? downloadsDirectory;
+    String? appSupportDirectory;
+    String? documentsDirectory;
     // Platform messages may fail, so we use a try/catch PlatformException.
     try {
       tempDirectory = await _provider.getTemporaryPath();

packages/path_provider/path_provider_linux/example/pubspec.yaml

@@ -3,19 +3,13 @@ description: Demonstrates how to use the path_provider_linux plugin.
 publish_to: "none"
 
 environment:
-  sdk: ">=2.1.0 <3.0.0"
+  sdk: ">=2.12.0-0 <3.0.0"
+  flutter: ">=1.10.0"
 
 dependencies:
   flutter:
     sdk: flutter
 
-  path_provider_linux: any
-
-  # The following adds the Cupertino Icons font to your application.
-  # Use with the CupertinoIcons class for iOS style icons.
-  cupertino_icons: ^0.1.3
-
-dependency_overrides:
   path_provider_linux:
     # When depending on this package from a real application you should use:
     #   path_provider_linux: ^x.y.z
@@ -32,39 +26,5 @@ dev_dependencies:
   integration_test:
     path: ../../../integration_test
 
-# For information on the generic Dart part of this file, see the
-# following page: https://dart.dev/tools/pub/pubspec
-
-# The following section is specific to Flutter.
 flutter:
-  # The following line ensures that the Material Icons font is
-  # included with your application, so that you can use the icons in
-  # the material Icons class.
   uses-material-design: true
-  # To add assets to your application, add an assets section, like this:
-  # assets:
-  #   - images/a_dot_burr.jpeg
-  #   - images/a_dot_ham.jpeg
-  # An image asset can refer to one or more resolution-specific "variants", see
-  # https://flutter.dev/assets-and-images/#resolution-aware.
-  # For details regarding adding assets from package dependencies, see
-  # https://flutter.dev/assets-and-images/#from-packages
-  # To add custom fonts to your application, add a fonts section here,
-  # in this "flutter" section. Each entry in this list should have a
-  # "family" key with the font family name, and a "fonts" key with a
-  # list giving the asset and other descriptors for the font. For
-  # example:
-  # fonts:
-  #   - family: Schyler
-  #     fonts:
-  #       - asset: fonts/Schyler-Regular.ttf
-  #       - asset: fonts/Schyler-Italic.ttf
-  #         style: italic
-  #   - family: Trajan Pro
-  #     fonts:
-  #       - asset: fonts/TrajanPro.ttf
-  #       - asset: fonts/TrajanPro_Bold.ttf
-  #         weight: 700
-  #
-  # For details regarding fonts from package dependencies,
-  # see https://flutter.dev/custom-fonts/#from-packages

packages/path_provider/path_provider_linux/example/test/widget_test.dart

@@ -30,7 +30,7 @@ void main() {
           find.byWidgetPredicate(
             (Widget widget) =>
                 widget is Text &&
-                widget.data.startsWith('Temp Directory: /tmp'),
+                widget.data!.startsWith('Temp Directory: /tmp'),
           ),
           findsOneWidget,
         );
@@ -48,7 +48,7 @@ void main() {
           find.byWidgetPredicate(
             (Widget widget) =>
                 widget is Text &&
-                widget.data.startsWith('Documents Directory: /'),
+                widget.data!.startsWith('Documents Directory: /'),
           ),
           findsOneWidget,
         );
@@ -66,7 +66,7 @@ void main() {
           find.byWidgetPredicate(
             (Widget widget) =>
                 widget is Text &&
-                widget.data.startsWith('Downloads Directory: /'),
+                widget.data!.startsWith('Downloads Directory: /'),
           ),
           findsOneWidget,
         );
@@ -85,7 +85,7 @@ void main() {
           find.byWidgetPredicate(
             (Widget widget) =>
                 widget is Text &&
-                widget.data.startsWith('Application Support Directory: /'),
+                widget.data!.startsWith('Application Support Directory: /'),
           ),
           findsOneWidget,
         );

packages/path_provider/path_provider_linux/example/test_driver/integration_test.dart

@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';

packages/path_provider/path_provider_macos/example/integration_test/path_provider_test.dart

@@ -2,42 +2,56 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import 'dart:io';
 import 'package:flutter_test/flutter_test.dart';
-import 'package:path_provider/path_provider.dart';
+import 'package:path_provider_platform_interface/path_provider_platform_interface.dart';
 import 'package:integration_test/integration_test.dart';
 
 void main() {
   IntegrationTestWidgetsFlutterBinding.ensureInitialized();
 
   testWidgets('getTemporaryDirectory', (WidgetTester tester) async {
-    final Directory result = await getTemporaryDirectory();
+    final PathProviderPlatform provider = PathProviderPlatform.instance;
+    final String result = await provider.getTemporaryPath();
     _verifySampleFile(result, 'temporaryDirectory');
   });
 
   testWidgets('getApplicationDocumentsDirectory', (WidgetTester tester) async {
-    final Directory result = await getApplicationDocumentsDirectory();
+    final PathProviderPlatform provider = PathProviderPlatform.instance;
+    final String result = await provider.getApplicationDocumentsPath();
     _verifySampleFile(result, 'applicationDocuments');
   });
 
   testWidgets('getApplicationSupportDirectory', (WidgetTester tester) async {
-    final Directory result = await getApplicationSupportDirectory();
+    final PathProviderPlatform provider = PathProviderPlatform.instance;
+    final String result = await provider.getApplicationSupportPath();
     _verifySampleFile(result, 'applicationSupport');
   });
 
   testWidgets('getLibraryDirectory', (WidgetTester tester) async {
-    if (!Platform.isMacOS) {
-      return;
-    }
-    final Directory result = await getLibraryDirectory();
+    final PathProviderPlatform provider = PathProviderPlatform.instance;
+    final String result = await provider.getLibraryPath();
     _verifySampleFile(result, 'library');
   });
+
+  testWidgets('getDownloadsDirectory', (WidgetTester tester) async {
+    final PathProviderPlatform provider = PathProviderPlatform.instance;
+    final String result = await provider.getDownloadsPath();
+    // _verifySampleFile causes hangs in driver for some reason, so just
+    // validate that a non-empty path was returned.
+    expect(result, isNotEmpty);
+  });
 }
 
-/// Verify a file called [name] in [directory] by recreating it with test
+/// Verify a file called [name] in [directoryPath] by recreating it with test
 /// contents when necessary.
-void _verifySampleFile(Directory directory, String name) {
-  final File file = File('${directory.path}/$name');
+///
+/// If [createDirectory] is true, the directory will be created if missing.
+void _verifySampleFile(String directoryPath, String name) {
+  final Directory directory = Directory(directoryPath);
+  final File file = File('${directory.path}${Platform.pathSeparator}$name');
 
   if (file.existsSync()) {
     file.deleteSync();