add default shared prefs tests

Author: tarrinneal

packages/shared_preferences/shared_preferences/README.md

@@ -50,20 +50,22 @@ latest data stored on the native platform regardless of what process was used to
 
 ### Android platform storage
 
-The [SharedPreferencesAsync] and [SharedPreferencesWithCache] APIs can use [DataStore Preferences](https://developer.android.com/topic/libraries/architecture/datastore) or [Android Shared Preferences](https://developer.android.com/reference/android/content/SharedPreferences) to store data.
+The [SharedPreferencesAsync] and [SharedPreferencesWithCache] APIs can use [DataStore Preferences](https://developer.android.com/topic/libraries/architecture/datastore) or [Android SharedPreferences](https://developer.android.com/reference/android/content/SharedPreferences) to store data.
+In most cases you should use the default option of DataStore Preferences, as it is the platform-recommended preferences storage system. 
+However, in some cases you may need to interact with preferences that were written to SharedPreferences by code you don't control.
 
-To use the `Android Shared Preferences` backend, use the `SharedPreferencesAsyncAndroidOptions` when using [SharedPreferencesAsync].
+To use the `Android SharedPreferences` backend, use the `SharedPreferencesAsyncAndroidOptions` when using [SharedPreferencesAsync] on Android.
 
 <?code-excerpt "readme_excerpts.dart (Android_Options)"?>
 ```dart
 const SharedPreferencesAsyncAndroidOptions options =
     SharedPreferencesAsyncAndroidOptions(
         backend: SharedPreferencesAndroidBackendLibrary.SharedPreferences,
         originalSharedPreferencesOptions:
-            OriginalSharedPreferencesOptions(fileName: 'the_name_of_a_file'));
+            AndroidSharedPreferencesStoreOptions(fileName: 'the_name_of_a_file'));
 ```
 
-The [SharedPreferences] API uses the native [Android Shared Preferences](https://developer.android.com/reference/android/content/SharedPreferences) tool to store data.
+The [SharedPreferences] API uses the native [Android SharedPreferences](https://developer.android.com/reference/android/content/SharedPreferences) tool to store data.
 
 ## Examples
 Here are small examples that show you how to use the API.

packages/shared_preferences/shared_preferences/example/lib/readme_excerpts.dart

@@ -98,6 +98,6 @@ Future<void> readmeTestSnippets() async {
 const SharedPreferencesAsyncAndroidOptions options =
     SharedPreferencesAsyncAndroidOptions(
         backend: SharedPreferencesAndroidBackendLibrary.SharedPreferences,
-        originalSharedPreferencesOptions:
-            OriginalSharedPreferencesOptions(fileName: 'the_name_of_a_file'));
+        originalSharedPreferencesOptions: AndroidSharedPreferencesStoreOptions(
+            fileName: 'the_name_of_a_file'));
 // #enddocregion Android_Options

packages/shared_preferences/shared_preferences_android/README.md

@@ -13,20 +13,20 @@ should add it to your `pubspec.yaml` as usual.
 
 ## Options
 
-The [SharedPreferencesAsync] and [SharedPreferencesWithCache] APIs can use [DataStore Preferences](https://developer.android.com/topic/libraries/architecture/datastore) or [Android Shared Preferences](https://developer.android.com/reference/android/content/SharedPreferences) to store data.
+The [SharedPreferencesAsync] and [SharedPreferencesWithCache] APIs can use [DataStore Preferences](https://developer.android.com/topic/libraries/architecture/datastore) or [Android SharedPreferences](https://developer.android.com/reference/android/content/SharedPreferences) to store data.
 
-To use the `Android Shared Preferences` backend, use the `SharedPreferencesAsyncAndroidOptions` when using [SharedPreferencesAsync].
+To use the `Android SharedPreferences` backend, use the `SharedPreferencesAsyncAndroidOptions` when using [SharedPreferencesAsync].
 
 <?code-excerpt "readme_excerpts.dart (Android_Options)"?>
 ```dart
 const SharedPreferencesAsyncAndroidOptions options =
     SharedPreferencesAsyncAndroidOptions(
         backend: SharedPreferencesAndroidBackendLibrary.SharedPreferences,
         originalSharedPreferencesOptions:
-            OriginalSharedPreferencesOptions(fileName: 'the_name_of_a_file'));
+            AndroidSharedPreferencesStoreOptions(fileName: 'the_name_of_a_file'));
 ```
 
-The [SharedPreferences] API uses the native [Android Shared Preferences](https://developer.android.com/reference/android/content/SharedPreferences) tool to store data.
+The [SharedPreferences] API uses the native [Android SharedPreferences](https://developer.android.com/reference/android/content/SharedPreferences) tool to store data.
 
 [1]: https://pub.dev/packages/shared_preferences
 [2]: https://flutter.dev/to/endorsed-federated-plugin

packages/shared_preferences/shared_preferences_android/android/src/main/kotlin/io/flutter/plugins/sharedpreferences/SharedPreferencesPlugin.kt

@@ -17,6 +17,7 @@ import androidx.datastore.preferences.core.edit
 import androidx.datastore.preferences.core.longPreferencesKey
 import androidx.datastore.preferences.core.stringPreferencesKey
 import androidx.datastore.preferences.preferencesDataStore
+import androidx.preference.PreferenceManager
 import io.flutter.embedding.engine.plugins.FlutterPlugin
 import io.flutter.plugin.common.BinaryMessenger
 import java.io.ByteArrayInputStream
@@ -243,8 +244,11 @@ class SharedPreferencesBackend(
   }
 
   private fun createSharedPreferences(options: SharedPreferencesPigeonOptions): SharedPreferences {
-    return context.getSharedPreferences(
-        options.fileName ?: SHARED_PREFERENCES_NAME, Context.MODE_PRIVATE)
+    return if (options.fileName == null) {
+      PreferenceManager.getDefaultSharedPreferences(context)
+    } else {
+      context.getSharedPreferences(options.fileName, Context.MODE_PRIVATE)
+    }
   }
 
   /** Adds property to data store of type bool. */

packages/shared_preferences/shared_preferences_android/android/src/test/kotlin/io/flutter/plugins/sharedpreferences/SharedPreferencesTest.kt

@@ -5,6 +5,8 @@
 package io.flutter.plugins.sharedpreferences
 
 import android.content.Context
+import android.content.SharedPreferences
+import androidx.preference.PreferenceManager
 import androidx.test.core.app.ApplicationProvider
 import androidx.test.ext.junit.runners.AndroidJUnit4
 import io.flutter.embedding.engine.plugins.FlutterPlugin
@@ -39,10 +41,9 @@ internal class SharedPreferencesTest {
 
   private val dataStoreOptions = SharedPreferencesPigeonOptions(useDataStore = true)
   private val sharedPreferencesOptions = SharedPreferencesPigeonOptions(useDataStore = false)
+  private val testContext: Context = ApplicationProvider.getApplicationContext()
 
   private fun pluginSetup(options: SharedPreferencesPigeonOptions): SharedPreferencesAsyncApi {
-    val testContext: Context = ApplicationProvider.getApplicationContext()
-
     val plugin = SharedPreferencesPlugin()
     val binaryMessenger = mockk<BinaryMessenger>()
     val flutterPluginBinding = mockk<FlutterPlugin.FlutterPluginBinding>()
@@ -311,4 +312,13 @@ internal class SharedPreferencesTest {
     Assert.assertEquals(plugin.getInt(intKey, sharedPreferencesOptions), 1L)
     Assert.assertEquals(plugin.getInt(intKey, optionsWithNewFile), 2L)
   }
+
+  @Test
+  fun testSharedPreferencesDefaultFile() {
+    val defaultPreferences: SharedPreferences =
+        PreferenceManager.getDefaultSharedPreferences(testContext)
+    defaultPreferences.edit().putString(stringKey, testString).commit()
+    val plugin = pluginSetup(sharedPreferencesOptions)
+    Assert.assertEquals(plugin.getString(stringKey, sharedPreferencesOptions), testString)
+  }
 }

packages/shared_preferences/shared_preferences_android/example/android/app/build.gradle

@@ -54,4 +54,5 @@ flutter {
 
 dependencies {
     implementation "androidx.datastore:datastore-preferences:1.0.0"
+    implementation 'androidx.preference:preference:1.2.1'
 }

packages/shared_preferences/shared_preferences_android/example/android/app/src/main/java/com/example/sharedpreferencesexample/MainActivity.java

@@ -0,0 +1,27 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package com.example.sharedpreferencesexample;
+
+import android.content.SharedPreferences;
+
+import androidx.annotation.NonNull;
+import androidx.preference.PreferenceManager;
+
+import io.flutter.embedding.android.FlutterActivity;
+import io.flutter.embedding.engine.FlutterEngine;
+
+public class MainActivity extends FlutterActivity {
+
+    @Override
+    public void configureFlutterEngine(@NonNull FlutterEngine flutterEngine) {
+        super.configureFlutterEngine(flutterEngine);
+        SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(
+                getApplicationContext());
+        preferences
+                .edit()
+                .putString("thisStringIsWrittenInTheExampleAppKotlinCode", "testString")
+                .commit();
+    }
+}

packages/shared_preferences/shared_preferences_android/example/integration_test/shared_preferences_test.dart

@@ -517,7 +517,7 @@ void main() {
           : SharedPreferencesAndroidBackendLibrary.SharedPreferences,
       originalSharedPreferencesOptions: fileName == null
           ? null
-          : OriginalSharedPreferencesOptions(fileName: fileName),
+          : AndroidSharedPreferencesStoreOptions(fileName: fileName),
     );
   }
 
@@ -782,4 +782,15 @@ void main() {
         await preferences.getInt(intKey, getOptions(false, fileName: 'file2')),
         2);
   });
+
+  testWidgets('Shared Preferences can read default sharedPreferences',
+      (WidgetTester _) async {
+    final SharedPreferencesAsyncPlatform preferences =
+        await getPreferences(false);
+
+    expect(
+        await preferences.getString(
+            'thisStringIsWrittenInTheExampleAppKotlinCode', getOptions(false)),
+        'testString');
+  });
 }

packages/shared_preferences/shared_preferences_android/example/lib/main.dart

@@ -16,8 +16,8 @@ void main() {
 const SharedPreferencesAsyncAndroidOptions options =
     SharedPreferencesAsyncAndroidOptions(
         backend: SharedPreferencesAndroidBackendLibrary.SharedPreferences,
-        originalSharedPreferencesOptions:
-            OriginalSharedPreferencesOptions(fileName: 'the_name_of_a_file'));
+        originalSharedPreferencesOptions: AndroidSharedPreferencesStoreOptions(
+            fileName: 'the_name_of_a_file'));
 // #enddocregion Android_Options
 
 class MyApp extends StatelessWidget {

packages/shared_preferences/shared_preferences_android/lib/src/shared_preferences_async_android.dart

@@ -257,25 +257,25 @@ class SharedPreferencesAsyncAndroidOptions extends SharedPreferencesOptions {
     this.originalSharedPreferencesOptions,
   });
 
-  /// Which backend should be used with
+  /// Which backend should be used for this method call.
   final SharedPreferencesAndroidBackendLibrary backend;
 
-  /// These options define how the `SharedPreferences` library should behave.
+  /// These options define how the `SharedPreferences` backend should behave.
   ///
   /// Any options in this field will be ignored unless the backend that is selected
   /// is `SharedPreferences`.
-  final OriginalSharedPreferencesOptions? originalSharedPreferencesOptions;
+  final AndroidSharedPreferencesStoreOptions? originalSharedPreferencesOptions;
 }
 
 /// Options necessary for defining the use of the original `SharedPreferences`
 /// library.
 ///
 /// These options are only ever used with the original `SharedPreferences` and
 /// have no purpose when using the default DataStore Preferences.
-class OriginalSharedPreferencesOptions {
-  /// Constructor for OriginalSharedPreferencesOptions.
-  const OriginalSharedPreferencesOptions({this.fileName = ''});
+class AndroidSharedPreferencesStoreOptions {
+  /// Constructor for AndroidSharedPreferencesStoreOptions.
+  const AndroidSharedPreferencesStoreOptions({this.fileName});
 
   /// The name of the file in which the preferences are stored.
-  final String fileName;
+  final String? fileName;
 }