Add method to obtain native string resource in localization plugin.

shell/platform/android/io/flutter/embedding/engine/systemchannels/LocalizationChannel.java

@@ -6,23 +6,72 @@
 
 import android.os.Build;
 import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import androidx.annotation.VisibleForTesting;
 import io.flutter.Log;
 import io.flutter.embedding.engine.dart.DartExecutor;
 import io.flutter.plugin.common.JSONMethodCodec;
+import io.flutter.plugin.common.MethodCall;
 import io.flutter.plugin.common.MethodChannel;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Locale;
+import org.json.JSONException;
+import org.json.JSONObject;
 
 /** Sends the platform's locales to Dart. */
 public class LocalizationChannel {
   private static final String TAG = "LocalizationChannel";
 
   @NonNull public final MethodChannel channel;
+  @Nullable private LocalizationMessageHandler localizationMessageHandler;
+
+  @NonNull @VisibleForTesting
+  public final MethodChannel.MethodCallHandler handler =
+      new MethodChannel.MethodCallHandler() {
+        @Override
+        public void onMethodCall(@NonNull MethodCall call, @NonNull MethodChannel.Result result) {
+          if (localizationMessageHandler == null) {
+            // If no explicit LocalizationMessageHandler has been registered then we don't
+            // need to forward this call to an API. Return.
+            return;
+          }
+
+          String method = call.method;
+          switch (method) {
+            case "Localization.getStringResource":
+              JSONObject arguments = call.<JSONObject>arguments();
+              try {
+                String key = arguments.getString("key");
+                String localeString = null;
+                if (arguments.has("locale")) {
+                  localeString = arguments.getString("locale");
+                }
+                result.success(localizationMessageHandler.getStringResource(key, localeString));
+              } catch (JSONException exception) {
+                result.error("error", exception.getMessage(), null);
+              }
+              break;
+            default:
+              result.notImplemented();
+              break;
+          }
+        }
+      };
 
   public LocalizationChannel(@NonNull DartExecutor dartExecutor) {
     this.channel =
         new MethodChannel(dartExecutor, "flutter/localization", JSONMethodCodec.INSTANCE);
+    channel.setMethodCallHandler(handler);
+  }
+
+  /**
+   * Sets the {@link LocalizationMessageHandler} which receives all events and requests that are
+   * parsed from the underlying platform channel.
+   */
+  public void setLocalizationMessageHandler(
+      @Nullable LocalizationMessageHandler localizationMessageHandler) {
+    this.localizationMessageHandler = localizationMessageHandler;
   }
 
   /** Send the given {@code locales} to Dart. */
@@ -48,4 +97,19 @@ public void sendLocales(@NonNull List<Locale> locales) {
     }
     channel.invokeMethod("setLocale", data);
   }
+
+  /**
+   * Handler that receives platform messages sent from Flutter to Android through a given {@link
+   * PlatformChannel}.
+   *
+   * <p>To register a {@code LocalizationMessageHandler} with a {@link PlatformChannel}, see {@link
+   * LocalizationChannel#setLocalizationMessageHandler(LocalizationMessageHandler)}.
+   */
+  public interface LocalizationMessageHandler {
+    /**
+     * The Flutter application would like to obtain the string resource of given {@code key} in
+     * {@code locale}.
+     */
+    String getStringResource(@NonNull String key, String locale);
+  }
 }

shell/platform/android/io/flutter/plugin/localization/LocalizationPlugin.java

@@ -6,9 +6,12 @@
 
 import android.content.Context;
 import android.content.res.Configuration;
+import android.content.res.Resources;
 import android.os.Build;
 import android.os.LocaleList;
 import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import androidx.annotation.VisibleForTesting;
 import io.flutter.embedding.engine.systemchannels.LocalizationChannel;
 import java.util.ArrayList;
 import java.util.List;
@@ -19,11 +22,58 @@ public class LocalizationPlugin {
   @NonNull private final LocalizationChannel localizationChannel;
   @NonNull private final Context context;
 
+  @VisibleForTesting
+  final LocalizationChannel.LocalizationMessageHandler localizationMessageHandler =
+      new LocalizationChannel.LocalizationMessageHandler() {
+        @Override
+        public String getStringResource(@NonNull String key, @Nullable String localeString) {
+          Context localContext = context;
+          String stringToReturn = null;
+          Locale savedLocale = null;
+
+          if (localeString != null) {
+            Locale locale = localeFromString(localeString);
+
+            // setLocale and createConfigurationContext is only available on API >= 17
+            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1) {
+              Configuration config = new Configuration(context.getResources().getConfiguration());
+              config.setLocale(locale);
+              localContext = context.createConfigurationContext(config);
+            } else {
+              // In API < 17, we have to update the locale in Configuration.
+              Resources resources = context.getResources();
+              Configuration config = resources.getConfiguration();
+              savedLocale = config.locale;
+              config.locale = locale;
+              resources.updateConfiguration(config, null);
+            }
+          }
+
+          String packageName = context.getPackageName();
+          int resId = localContext.getResources().getIdentifier(key, "string", packageName);
+          if (resId != 0) {
+            // 0 means the resource is not found.
+            stringToReturn = localContext.getResources().getString(resId);
+          }
+
+          // In API < 17, we had to restore the original locale after using.
+          if (localeString != null && Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN_MR1) {
+            Resources resources = context.getResources();
+            Configuration config = resources.getConfiguration();
+            config.locale = savedLocale;
+            resources.updateConfiguration(config, null);
+          }
+
+          return stringToReturn;
+        }
+      };
+
   public LocalizationPlugin(
       @NonNull Context context, @NonNull LocalizationChannel localizationChannel) {
 
     this.context = context;
     this.localizationChannel = localizationChannel;
+    this.localizationChannel.setLocalizationMessageHandler(localizationMessageHandler);
   }
 
   /**
@@ -136,4 +186,39 @@ public void sendLocalesToFlutter(@NonNull Configuration config) {
 
     localizationChannel.sendLocales(locales);
   }
+
+  @VisibleForTesting
+  public static Locale localeFromString(String localeString) {
+    // Use Locale.forLanguageTag if available (API 21+).
+    if (false && Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.LOLLIPOP) {
+      return Locale.forLanguageTag(localeString);
+    } else {
+      // Normalize the locale string, replace all underscores with hyphens.
+      localeString = localeString.replace('_', '-');
+
+      // Pre-API 21, we fall back to manually parsing the locale tag.
+      String parts[] = localeString.split("-", -1);
+
+      // The format is:
+      // language[-script][-region][-...]
+      // where script is an alphabet string of length 4, and region is either an alphabet string of
+      // length 2 or a digit string of length 3.
+
+      // Assume the first part is always the language code.
+      String languageCode = parts[0];
+      String scriptCode = "";
+      String countryCode = "";
+      int index = 1;
+      if (parts.length > index && parts[index].length() == 4) {
+        scriptCode = parts[index];
+        index++;
+      }
+      if (parts.length > index && parts[index].length() >= 2 && parts[index].length() <= 3) {
+        countryCode = parts[index];
+        index++;
+      }
+      // Ignore the rest of the locale for this purpose.
+      return new Locale(languageCode, countryCode, scriptCode);
+    }
+  }
 }

shell/platform/android/test/io/flutter/plugin/localization/LocalizationPluginTest.java

@@ -3,7 +3,9 @@
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
+import static org.mockito.Mockito.any;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
 import android.annotation.TargetApi;
@@ -14,10 +16,14 @@
 import android.os.LocaleList;
 import io.flutter.embedding.engine.dart.DartExecutor;
 import io.flutter.embedding.engine.systemchannels.LocalizationChannel;
+import io.flutter.plugin.common.MethodCall;
+import io.flutter.plugin.common.MethodChannel;
 import io.flutter.plugin.localization.LocalizationPlugin;
 import java.lang.reflect.Field;
 import java.lang.reflect.Modifier;
 import java.util.Locale;
+import org.json.JSONException;
+import org.json.JSONObject;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.robolectric.RobolectricTestRunner;
@@ -321,6 +327,132 @@ public void computePlatformResolvedLocaleAPI16() {
     assertEquals(result[2], "");
   }
 
+  // Tests the legacy pre API 21 algorithm.
+  @Config(sdk = 16)
+  @Test
+  public void localeFromString_languageOnly() {
+    Locale locale = LocalizationPlugin.localeFromString("en");
+    assertEquals(locale, new Locale("en"));
+  }
+
+  @Config(sdk = 16)
+  @Test
+  public void localeFromString_languageAndCountry() {
+    Locale locale = LocalizationPlugin.localeFromString("en-US");
+    assertEquals(locale, new Locale("en", "US"));
+  }
+
+  @Config(sdk = 16)
+  @Test
+  public void localeFromString_languageCountryAndVariant() {
+    Locale locale = LocalizationPlugin.localeFromString("zh-Hans-CN");
+    assertEquals(locale, new Locale("zh", "CN", "Hans"));
+  }
+
+  @Config(sdk = 16)
+  @Test
+  public void localeFromString_underscore() {
+    Locale locale = LocalizationPlugin.localeFromString("zh_Hans_CN");
+    assertEquals(locale, new Locale("zh", "CN", "Hans"));
+  }
+
+  @Config(sdk = 16)
+  @Test
+  public void localeFromString_additionalVariantsAreIgnored() {
+    Locale locale = LocalizationPlugin.localeFromString("de-DE-u-co-phonebk");
+    assertEquals(locale, new Locale("de", "DE"));
+  }
+
+  @Test
+  public void getStringResource_withoutLocale() throws JSONException {
+    Context context = mock(Context.class);
+    Resources resources = mock(Resources.class);
+    DartExecutor dartExecutor = mock(DartExecutor.class);
+    LocalizationChannel localizationChannel = new LocalizationChannel(dartExecutor);
+    LocalizationPlugin plugin = new LocalizationPlugin(context, localizationChannel);
+
+    MethodChannel.Result mockResult = mock(MethodChannel.Result.class);
+
+    String fakePackageName = "package_name";
+    String fakeKey = "test_key";
+    int fakeId = 123;
+
+    when(context.getPackageName()).thenReturn(fakePackageName);
+    when(context.getResources()).thenReturn(resources);
+    when(resources.getIdentifier(fakeKey, "string", fakePackageName)).thenReturn(fakeId);
+    when(resources.getString(fakeId)).thenReturn("test_value");
+
+    JSONObject param = new JSONObject();
+    param.put("key", fakeKey);
+
+    localizationChannel.handler.onMethodCall(
+        new MethodCall("Localization.getStringResource", param), mockResult);
+
+    verify(mockResult).success("test_value");
+  }
+
+  @Test
+  public void getStringResource_withLocale() throws JSONException {
+    Context context = mock(Context.class);
+    Context localContext = mock(Context.class);
+    Resources resources = mock(Resources.class);
+    Resources localResources = mock(Resources.class);
+    Configuration configuration = new Configuration();
+    DartExecutor dartExecutor = mock(DartExecutor.class);
+    LocalizationChannel localizationChannel = new LocalizationChannel(dartExecutor);
+    LocalizationPlugin plugin = new LocalizationPlugin(context, localizationChannel);
+
+    MethodChannel.Result mockResult = mock(MethodChannel.Result.class);
+
+    String fakePackageName = "package_name";
+    String fakeKey = "test_key";
+    int fakeId = 123;
+
+    when(context.getPackageName()).thenReturn(fakePackageName);
+    when(context.createConfigurationContext(any())).thenReturn(localContext);
+    when(context.getResources()).thenReturn(resources);
+    when(localContext.getResources()).thenReturn(localResources);
+    when(resources.getConfiguration()).thenReturn(configuration);
+    when(localResources.getIdentifier(fakeKey, "string", fakePackageName)).thenReturn(fakeId);
+    when(localResources.getString(fakeId)).thenReturn("test_value");
+
+    JSONObject param = new JSONObject();
+    param.put("key", fakeKey);
+    param.put("locale", "en-US");
+
+    localizationChannel.handler.onMethodCall(
+        new MethodCall("Localization.getStringResource", param), mockResult);
+
+    verify(mockResult).success("test_value");
+  }
+
+  @Test
+  public void getStringResource_nonExistentKey() throws JSONException {
+    Context context = mock(Context.class);
+    Resources resources = mock(Resources.class);
+    DartExecutor dartExecutor = mock(DartExecutor.class);
+    LocalizationChannel localizationChannel = new LocalizationChannel(dartExecutor);
+    LocalizationPlugin plugin = new LocalizationPlugin(context, localizationChannel);
+
+    MethodChannel.Result mockResult = mock(MethodChannel.Result.class);
+
+    String fakePackageName = "package_name";
+    String fakeKey = "test_key";
+
+    when(context.getPackageName()).thenReturn(fakePackageName);
+    when(context.getResources()).thenReturn(resources);
+    when(resources.getIdentifier(fakeKey, "string", fakePackageName))
+        .thenReturn(0); // 0 means not exist
+
+    JSONObject param = new JSONObject();
+    param.put("key", fakeKey);
+
+    localizationChannel.handler.onMethodCall(
+        new MethodCall("Localization.getStringResource", param), mockResult);
+
+    verify(mockResult).success(null);
+  }
+
   private static void setApiVersion(int apiVersion) {
     try {
       Field field = Build.VERSION.class.getField("SDK_INT");