Support loading assets from Android dynamic feature modules (flutter#21504)

Initialize the AssetManager from the application context so that assets from dynamic feature modules can be loaded.

Author: chingjun

shell/platform/android/io/flutter/embedding/engine/FlutterEngine.java

@@ -5,6 +5,8 @@
 package io.flutter.embedding.engine;
 
 import android.content.Context;
+import android.content.pm.PackageManager.NameNotFoundException;
+import android.content.res.AssetManager;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import io.flutter.FlutterInjector;
@@ -264,7 +266,13 @@ public FlutterEngine(
       @Nullable String[] dartVmArgs,
       boolean automaticallyRegisterPlugins,
       boolean waitForRestorationData) {
-    this.dartExecutor = new DartExecutor(flutterJNI, context.getAssets());
+    AssetManager assetManager;
+    try {
+      assetManager = context.createPackageContext(context.getPackageName(), 0).getAssets();
+    } catch (NameNotFoundException e) {
+      assetManager = context.getAssets();
+    }
+    this.dartExecutor = new DartExecutor(flutterJNI, assetManager);
     this.dartExecutor.onAttachedToJNI();
 
     accessibilityChannel = new AccessibilityChannel(dartExecutor, flutterJNI);

shell/platform/android/test/io/flutter/embedding/engine/FlutterEngineTest.java

@@ -4,13 +4,15 @@
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
 import static org.mockito.Mockito.any;
+import static org.mockito.Mockito.anyInt;
 import static org.mockito.Mockito.atLeast;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
 import android.content.Context;
+import android.content.pm.PackageManager.NameNotFoundException;
 import io.flutter.FlutterInjector;
 import io.flutter.embedding.engine.FlutterEngine;
 import io.flutter.embedding.engine.FlutterJNI;
@@ -127,8 +129,11 @@ public void itNotifiesPlatformViewsControllerAboutJNILifecycle() {
   }
 
   @Test
-  public void itUsesApplicationContext() {
+  public void itUsesApplicationContext() throws NameNotFoundException {
     Context context = mock(Context.class);
+    Context packageContext = mock(Context.class);
+
+    when(context.createPackageContext(any(), anyInt())).thenReturn(packageContext);
 
     new FlutterEngine(
         context,
@@ -141,12 +146,32 @@ public void itUsesApplicationContext() {
   }
 
   @Test
-  public void itCanUseFlutterLoaderInjectionViaFlutterInjector() {
+  public void itUsesPackageContextForAssetManager() throws NameNotFoundException {
+    Context context = mock(Context.class);
+    Context packageContext = mock(Context.class);
+    when(context.createPackageContext(any(), anyInt())).thenReturn(packageContext);
+
+    new FlutterEngine(
+        context,
+        mock(FlutterLoader.class),
+        flutterJNI,
+        /*dartVmArgs=*/ new String[] {},
+        /*automaticallyRegisterPlugins=*/ false);
+
+    verify(packageContext, atLeast(1)).getAssets();
+    verify(context, times(0)).getAssets();
+  }
+
+  @Test
+  public void itCanUseFlutterLoaderInjectionViaFlutterInjector() throws NameNotFoundException {
     FlutterInjector.reset();
     FlutterLoader mockFlutterLoader = mock(FlutterLoader.class);
     FlutterInjector.setInstance(
         new FlutterInjector.Builder().setFlutterLoader(mockFlutterLoader).build());
     Context mockContext = mock(Context.class);
+    Context packageContext = mock(Context.class);
+
+    when(mockContext.createPackageContext(any(), anyInt())).thenReturn(packageContext);
 
     new FlutterEngine(mockContext, null, flutterJNI);