[shared_preferences_windows]-Migrate to null safety (flutter#3516)

Migrate shared_preferences_windows to null safety

Author: Sameerkash

packages/shared_preferences/shared_preferences_windows/CHANGELOG.md

@@ -1,3 +1,8 @@
+
+## 0.0.3-nullsafety
+
+* Migrate to null-safety.
+
 ## 0.0.2+3
 
 * Remove 'ffi' dependency.

packages/shared_preferences/shared_preferences_windows/lib/shared_preferences_windows.dart

@@ -27,42 +27,51 @@ class SharedPreferencesWindows extends SharedPreferencesStorePlatform {
   PathProviderWindows pathProvider = PathProviderWindows();
 
   /// Local copy of preferences
-  Map<String, Object> _cachedPreferences;
+  Map<String, Object>? _cachedPreferences;
 
   /// Cached file for storing preferences.
-  File _localDataFilePath;
+  File? _localDataFilePath;
 
   /// Gets the file where the preferences are stored.
-  Future<File> _getLocalDataFile() async {
-    if (_localDataFilePath == null) {
-      final directory = await pathProvider.getApplicationSupportPath();
-      _localDataFilePath =
-          fs.file(path.join(directory, 'shared_preferences.json'));
+  Future<File?> _getLocalDataFile() async {
+    if (_localDataFilePath != null) {
+      return _localDataFilePath!;
     }
-    return _localDataFilePath;
+    final directory = await pathProvider.getApplicationSupportPath();
+    if (directory == null) {
+      return null;
+    }
+    return _localDataFilePath =
+        fs.file(path.join(directory, 'shared_preferences.json'));
   }
 
   /// Gets the preferences from the stored file. Once read, the preferences are
   /// maintained in memory.
   Future<Map<String, Object>> _readPreferences() async {
-    if (_cachedPreferences == null) {
-      _cachedPreferences = {};
-      File localDataFile = await _getLocalDataFile();
-      if (localDataFile.existsSync()) {
-        String stringMap = localDataFile.readAsStringSync();
-        if (stringMap.isNotEmpty) {
-          _cachedPreferences = json.decode(stringMap) as Map<String, Object>;
-        }
+    if (_cachedPreferences != null) {
+      return _cachedPreferences!;
+    }
+    Map<String, Object> preferences = {};
+    final File? localDataFile = await _getLocalDataFile();
+    if (localDataFile != null && localDataFile.existsSync()) {
+      String stringMap = localDataFile.readAsStringSync();
+      if (stringMap.isNotEmpty) {
+        preferences = json.decode(stringMap).cast<String, Object>();
       }
     }
-    return _cachedPreferences;
+    _cachedPreferences = preferences;
+    return preferences;
   }
 
   /// Writes the cached preferences to disk. Returns [true] if the operation
   /// succeeded.
   Future<bool> _writePreferences(Map<String, Object> preferences) async {
     try {
-      File localDataFile = await _getLocalDataFile();
+      final File? localDataFile = await _getLocalDataFile();
+      if (localDataFile == null) {
+        print("Unable to determine where to write preferences.");
+        return false;
+      }
       if (!localDataFile.existsSync()) {
         localDataFile.createSync(recursive: true);
       }

packages/shared_preferences/shared_preferences_windows/pubspec.yaml

@@ -1,7 +1,8 @@
 name: shared_preferences_windows
 description: Windows implementation of shared_preferences
 homepage: https://github.com/flutter/plugins/tree/master/packages/shared_preferences/shared_preferences_windows
-version: 0.0.2+3
+version: 0.0.3-nullsafety
+
 
 flutter:
   plugin:
@@ -11,20 +12,20 @@ flutter:
         pluginClass: none
 
 environment:
-  sdk: ">=2.1.0 <3.0.0"
+  sdk: '>=2.12.0-0 <3.0.0'
   flutter: ">=1.12.8"
 
 dependencies:
-  shared_preferences_platform_interface: ^1.0.0
+  shared_preferences_platform_interface: ^2.0.0-nullsafety
   flutter:
     sdk: flutter
-  file: ">=5.1.0 <7.0.0"
+  file: ^6.0.0-nullsafety.4
   meta: ^1.1.7
   path: ^1.6.4
-  path_provider_platform_interface: ^1.0.3
-  path_provider_windows: ^0.0.2
+  path_provider_platform_interface: ^2.0.0-nullsafety
+  path_provider_windows: ^0.1.0-nullsafety.2
 
 dev_dependencies:
   flutter_test:
     sdk: flutter
-  pedantic: ^1.8.0
+  pedantic: ^1.10.0-nullsafety.3

packages/shared_preferences/shared_preferences_windows/test/shared_preferences_windows_test.dart

@@ -10,8 +10,8 @@ import 'package:path_provider_windows/path_provider_windows.dart';
 import 'package:shared_preferences_windows/shared_preferences_windows.dart';
 
 void main() {
-  MemoryFileSystem fileSystem;
-  PathProviderWindows pathProvider;
+  late MemoryFileSystem fileSystem;
+  late PathProviderWindows pathProvider;
 
   setUp(() {
     fileSystem = MemoryFileSystem.test();
@@ -22,7 +22,7 @@ void main() {
 
   Future<String> _getFilePath() async {
     final directory = await pathProvider.getApplicationSupportPath();
-    return path.join(directory, 'shared_preferences.json');
+    return path.join(directory!, 'shared_preferences.json');
   }
 
   _writeTestFile(String value) async {
@@ -87,23 +87,23 @@ void main() {
 /// path it returns is a root path that does not actually exist on Windows.
 class FakePathProviderWindows extends PathProviderPlatform
     implements PathProviderWindows {
-  VersionInfoQuerier versionInfoQuerier;
+  late VersionInfoQuerier versionInfoQuerier;
 
   @override
-  Future<String> getApplicationSupportPath() async => r'C:\appsupport';
+  Future<String?> getApplicationSupportPath() async => r'C:\appsupport';
 
   @override
-  Future<String> getTemporaryPath() async => null;
+  Future<String?> getTemporaryPath() async => null;
 
   @override
-  Future<String> getLibraryPath() async => null;
+  Future<String?> getLibraryPath() async => null;
 
   @override
-  Future<String> getApplicationDocumentsPath() async => null;
+  Future<String?> getApplicationDocumentsPath() async => null;
 
   @override
-  Future<String> getDownloadsPath() async => null;
+  Future<String?> getDownloadsPath() async => null;
 
   @override
-  Future<String> getPath(String folderID) async => null;
+  Future<String> getPath(String folderID) async => '';
 }