Fix accessibility of embedded views in Android 9 and below (flutter/engine#25709)

engine/src/flutter/shell/platform/android/BUILD.gn

@@ -456,6 +456,7 @@ action("robolectric_tests") {
     "test/io/flutter/FlutterInjectorTest.java",
     "test/io/flutter/FlutterTestSuite.java",
     "test/io/flutter/SmokeTest.java",
+    "test/io/flutter/TestUtils.java",
     "test/io/flutter/embedding/android/AndroidKeyProcessorTest.java",
     "test/io/flutter/embedding/android/FlutterActivityAndFragmentDelegateTest.java",
     "test/io/flutter/embedding/android/FlutterActivityTest.java",

engine/src/flutter/shell/platform/android/io/flutter/embedding/android/FlutterView.java

@@ -20,6 +20,7 @@ import android.view.MotionEvent;
 import android.view.PointerIcon;
 import android.view.Surface;
 import android.view.View;
+import android.view.ViewGroup;
 import android.view.ViewStructure;
 import android.view.WindowInsets;
 import android.view.WindowManager;
@@ -44,6 +45,8 @@ import io.flutter.plugin.localization.LocalizationPlugin;
 import io.flutter.plugin.mouse.MouseCursorPlugin;
 import io.flutter.plugin.platform.PlatformViewsController;
 import io.flutter.view.AccessibilityBridge;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
 import java.util.HashSet;
 import java.util.Set;
 
@@ -826,6 +829,84 @@ public class FlutterView extends FrameLayout implements MouseCursorPlugin.MouseC
     }
   }
 
+  /**
+   * Prior to Android Q, it's impossible to add real views as descendants of virtual nodes. This
+   * breaks accessibility when an Android view is embedded in a Flutter app.
+   *
+   * <p>This method overrides a @hide method in {@code ViewGroup} to workaround this limitation.
+   * This solution is derivated from Jetpack Compose, and can be found in the Android source code as
+   * well.
+   *
+   * <p>This workaround finds the descendant {@code View} that matches the provided accessibility
+   * id.
+   *
+   * @param accessibilityId The view accessibility id.
+   * @return The view matching the accessibility id if any.
+   */
+  @SuppressLint("PrivateApi")
+  public View findViewByAccessibilityIdTraversal(int accessibilityId) {
+    if (Build.VERSION.SDK_INT < Build.VERSION_CODES.Q) {
+      return findViewByAccessibilityIdRootedAtCurrentView(accessibilityId, this);
+    }
+    // Android Q or later doesn't call this method.
+    //
+    // However, since this is implementation detail, a future version of Android might call
+    // this method again, fallback to calling the @hide method as expected by ViewGroup.
+    Method findViewByAccessibilityIdTraversalMethod;
+    try {
+      findViewByAccessibilityIdTraversalMethod =
+          View.class.getDeclaredMethod("findViewByAccessibilityIdTraversal", int.class);
+    } catch (NoSuchMethodException exception) {
+      return null;
+    }
+    findViewByAccessibilityIdTraversalMethod.setAccessible(true);
+    try {
+      return (View) findViewByAccessibilityIdTraversalMethod.invoke(this, accessibilityId);
+    } catch (IllegalAccessException exception) {
+      return null;
+    } catch (InvocationTargetException exception) {
+      return null;
+    }
+  }
+
+  /**
+   * Finds the descendant view that matches the provided accessibility id.
+   *
+   * @param accessibilityId The view accessibility id.
+   * @param currentView The root view.
+   * @return A descendant of currentView or currentView itself.
+   */
+  @SuppressLint("PrivateApi")
+  private View findViewByAccessibilityIdRootedAtCurrentView(int accessibilityId, View currentView) {
+    Method getAccessibilityViewIdMethod;
+    try {
+      getAccessibilityViewIdMethod = View.class.getDeclaredMethod("getAccessibilityViewId");
+    } catch (NoSuchMethodException exception) {
+      return null;
+    }
+    getAccessibilityViewIdMethod.setAccessible(true);
+    try {
+      if (getAccessibilityViewIdMethod.invoke(currentView).equals(accessibilityId)) {
+        return currentView;
+      }
+    } catch (IllegalAccessException exception) {
+      return null;
+    } catch (InvocationTargetException exception) {
+      return null;
+    }
+    if (currentView instanceof ViewGroup) {
+      for (int i = 0; i < ((ViewGroup) currentView).getChildCount(); i++) {
+        View view =
+            findViewByAccessibilityIdRootedAtCurrentView(
+                accessibilityId, ((ViewGroup) currentView).getChildAt(i));
+        if (view != null) {
+          return view;
+        }
+      }
+    }
+    return null;
+  }
+
   // TODO(mattcarroll): Confer with Ian as to why we need this method. Delete if possible, otherwise
   // add comments.
   private void resetWillNotDraw(boolean isAccessibilityEnabled, boolean isTouchExplorationEnabled) {

engine/src/flutter/shell/platform/android/test/io/flutter/TestUtils.java

@@ -0,0 +1,45 @@
+// 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 io.flutter;
+
+import static org.junit.Assert.assertTrue;
+
+import android.content.res.Configuration;
+import android.os.Build;
+import java.lang.reflect.Field;
+import java.lang.reflect.Modifier;
+import java.util.Locale;
+
+public class TestUtils {
+
+  public static void setApiVersion(int apiVersion) {
+    try {
+      Field field = Build.VERSION.class.getField("SDK_INT");
+
+      field.setAccessible(true);
+      Field modifiersField = Field.class.getDeclaredField("modifiers");
+      modifiersField.setAccessible(true);
+      modifiersField.setInt(field, field.getModifiers() & ~Modifier.FINAL);
+
+      field.set(null, apiVersion);
+    } catch (Exception e) {
+      assertTrue(false);
+    }
+  }
+
+  public static void setLegacyLocale(Configuration config, Locale locale) {
+    try {
+      Field field = config.getClass().getField("locale");
+      field.setAccessible(true);
+      Field modifiersField = Field.class.getDeclaredField("modifiers");
+      modifiersField.setAccessible(true);
+      modifiersField.setInt(field, field.getModifiers() & ~Modifier.FINAL);
+
+      field.set(config, locale);
+    } catch (Exception e) {
+      assertTrue(false);
+    }
+  }
+}

engine/src/flutter/shell/platform/android/test/io/flutter/embedding/android/FlutterViewTest.java

@@ -28,12 +28,15 @@ import android.view.View;
 import android.view.ViewGroup;
 import android.view.WindowInsets;
 import android.view.WindowManager;
+import android.widget.FrameLayout;
+import io.flutter.TestUtils;
 import io.flutter.embedding.engine.FlutterEngine;
 import io.flutter.embedding.engine.FlutterJNI;
 import io.flutter.embedding.engine.loader.FlutterLoader;
 import io.flutter.embedding.engine.renderer.FlutterRenderer;
 import io.flutter.embedding.engine.systemchannels.SettingsChannel;
 import io.flutter.plugin.platform.PlatformViewsController;
+import java.lang.reflect.Method;
 import java.util.concurrent.atomic.AtomicReference;
 import org.junit.Before;
 import org.junit.Test;
@@ -745,6 +748,50 @@ public class FlutterViewTest {
     verify(mockRegion, times(1)).op(0, 0, 0, 0, Region.Op.DIFFERENCE);
   }
 
+  @Test
+  @SuppressLint("PrivateApi")
+  public void findViewByAccessibilityIdTraversal_returnsRootViewOnAndroid28() throws Exception {
+    TestUtils.setApiVersion(28);
+
+    FlutterView flutterView = new FlutterView(RuntimeEnvironment.application);
+
+    Method getAccessibilityViewIdMethod = View.class.getDeclaredMethod("getAccessibilityViewId");
+    Integer accessibilityViewId = (Integer) getAccessibilityViewIdMethod.invoke(flutterView);
+
+    assertEquals(flutterView, flutterView.findViewByAccessibilityIdTraversal(accessibilityViewId));
+  }
+
+  @Test
+  @SuppressLint("PrivateApi")
+  public void findViewByAccessibilityIdTraversal_returnsChildViewOnAndroid28() throws Exception {
+    TestUtils.setApiVersion(28);
+
+    FlutterView flutterView = new FlutterView(RuntimeEnvironment.application);
+    FrameLayout childView1 = new FrameLayout(RuntimeEnvironment.application);
+    flutterView.addView(childView1);
+
+    FrameLayout childView2 = new FrameLayout(RuntimeEnvironment.application);
+    childView1.addView(childView2);
+
+    Method getAccessibilityViewIdMethod = View.class.getDeclaredMethod("getAccessibilityViewId");
+    Integer accessibilityViewId = (Integer) getAccessibilityViewIdMethod.invoke(childView2);
+
+    assertEquals(childView2, flutterView.findViewByAccessibilityIdTraversal(accessibilityViewId));
+  }
+
+  @Test
+  @SuppressLint("PrivateApi")
+  public void findViewByAccessibilityIdTraversal_returnsRootViewOnAndroid29() throws Exception {
+    TestUtils.setApiVersion(29);
+
+    FlutterView flutterView = new FlutterView(RuntimeEnvironment.application);
+
+    Method getAccessibilityViewIdMethod = View.class.getDeclaredMethod("getAccessibilityViewId");
+    Integer accessibilityViewId = (Integer) getAccessibilityViewIdMethod.invoke(flutterView);
+
+    assertEquals(null, flutterView.findViewByAccessibilityIdTraversal(accessibilityViewId));
+  }
+
   /*
    * A custom shadow that reports fullscreen flag for system UI visibility
    */

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

@@ -2,7 +2,6 @@
 package io.flutter.embedding.engine;
 
 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;
@@ -12,15 +11,13 @@ import android.annotation.TargetApi;
 import android.content.Context;
 import android.content.res.Configuration;
 import android.content.res.Resources;
-import android.os.Build;
 import android.os.LocaleList;
+import io.flutter.TestUtils;
 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;
@@ -37,7 +34,7 @@ public class LocalizationPluginTest {
   @Test
   public void computePlatformResolvedLocaleAPI26() {
     // --- Test Setup ---
-    setApiVersion(26);
+    TestUtils.setApiVersion(26);
     FlutterJNI flutterJNI = new FlutterJNI();
 
     Context context = mock(Context.class);
@@ -145,7 +142,7 @@ public class LocalizationPluginTest {
   @Test
   public void computePlatformResolvedLocaleAPI24() {
     // --- Test Setup ---
-    setApiVersion(24);
+    TestUtils.setApiVersion(24);
     FlutterJNI flutterJNI = new FlutterJNI();
 
     Context context = mock(Context.class);
@@ -240,7 +237,7 @@ public class LocalizationPluginTest {
   @Test
   public void computePlatformResolvedLocaleAPI16() {
     // --- Test Setup ---
-    setApiVersion(16);
+    TestUtils.setApiVersion(16);
     FlutterJNI flutterJNI = new FlutterJNI();
 
     Context context = mock(Context.class);
@@ -250,7 +247,7 @@ public class LocalizationPluginTest {
     Locale userLocale = new Locale("es", "MX");
     when(context.getResources()).thenReturn(resources);
     when(resources.getConfiguration()).thenReturn(config);
-    setLegacyLocale(config, userLocale);
+    TestUtils.setLegacyLocale(config, userLocale);
 
     flutterJNI.setLocalizationPlugin(
         new LocalizationPlugin(context, new LocalizationChannel(dartExecutor)));
@@ -268,7 +265,7 @@ public class LocalizationPluginTest {
           "en", "CA", ""
         };
     userLocale = null;
-    setLegacyLocale(config, userLocale);
+    TestUtils.setLegacyLocale(config, userLocale);
     result = flutterJNI.computePlatformResolvedLocale(supportedLocales);
     // The first locale is default.
     assertEquals(result.length, 3);
@@ -286,7 +283,7 @@ public class LocalizationPluginTest {
           "it", "IT", ""
         };
     userLocale = new Locale("fr", "CH");
-    setLegacyLocale(config, userLocale);
+    TestUtils.setLegacyLocale(config, userLocale);
     result = flutterJNI.computePlatformResolvedLocale(supportedLocales);
     assertEquals(result.length, 3);
     assertEquals(result[0], "en");
@@ -302,7 +299,7 @@ public class LocalizationPluginTest {
           "it", "IT", ""
         };
     userLocale = new Locale("it", "IT");
-    setLegacyLocale(config, userLocale);
+    TestUtils.setLegacyLocale(config, userLocale);
     result = flutterJNI.computePlatformResolvedLocale(supportedLocales);
     assertEquals(result.length, 3);
     assertEquals(result[0], "it");
@@ -319,7 +316,7 @@ public class LocalizationPluginTest {
           "it", "IT", ""
         };
     userLocale = new Locale("fr", "CH");
-    setLegacyLocale(config, userLocale);
+    TestUtils.setLegacyLocale(config, userLocale);
     result = flutterJNI.computePlatformResolvedLocale(supportedLocales);
     assertEquals(result.length, 3);
     assertEquals(result[0], "fr");
@@ -452,33 +449,4 @@ public class LocalizationPluginTest {
 
     verify(mockResult).success(null);
   }
-
-  private static void setApiVersion(int apiVersion) {
-    try {
-      Field field = Build.VERSION.class.getField("SDK_INT");
-
-      field.setAccessible(true);
-      Field modifiersField = Field.class.getDeclaredField("modifiers");
-      modifiersField.setAccessible(true);
-      modifiersField.setInt(field, field.getModifiers() & ~Modifier.FINAL);
-
-      field.set(null, apiVersion);
-    } catch (Exception e) {
-      assertTrue(false);
-    }
-  }
-
-  private static void setLegacyLocale(Configuration config, Locale locale) {
-    try {
-      Field field = config.getClass().getField("locale");
-      field.setAccessible(true);
-      Field modifiersField = Field.class.getDeclaredField("modifiers");
-      modifiersField.setAccessible(true);
-      modifiersField.setInt(field, field.getModifiers() & ~Modifier.FINAL);
-
-      field.set(config, locale);
-    } catch (Exception e) {
-      assertTrue(false);
-    }
-  }
 }