Automatically register plugins for FlutterFragmentActivity

shell/platform/android/io/flutter/embedding/android/FlutterFragmentActivity.java

@@ -41,6 +41,7 @@
 import io.flutter.embedding.engine.FlutterShellArgs;
 import io.flutter.plugin.platform.PlatformPlugin;
 import io.flutter.view.FlutterMain;
+import java.lang.reflect.Method;
 
 /**
  * A Flutter {@code Activity} that is based upon {@link FragmentActivity}.
@@ -555,13 +556,18 @@ public FlutterEngine provideFlutterEngine(@NonNull Context context) {
   }
 
   /**
-   * Hook for subclasses to easily configure a {@code FlutterEngine}, e.g., register plugins.
+   * Hook for subclasses to easily configure a {@code FlutterEngine}.
    *
    * <p>This method is called after {@link #provideFlutterEngine(Context)}.
+   *
+   * <p>All plugins listed in the app's pubspec are registered in the base implementation of this
+   * method. To avoid automatic plugin registration, override this method without invoking super().
+   * To keep automatic plugin registration and further configure the flutterEngine, override this
+   * method, invoke super(), and then configure the flutterEngine as desired.
    */
   @Override
   public void configureFlutterEngine(@NonNull FlutterEngine flutterEngine) {
-    // No-op. Hook for subclasses.
+    registerPlugins(flutterEngine);
   }
 
   /**
@@ -698,4 +704,34 @@ protected BackgroundMode getBackgroundMode() {
   private boolean isDebuggable() {
     return (getApplicationInfo().flags & ApplicationInfo.FLAG_DEBUGGABLE) != 0;
   }
+
+  /**
+   * Registers all plugins that an app lists in its pubspec.yaml.
+   *
+   * <p>The Flutter tool generates a class called GeneratedPluginRegistrant, which includes the code
+   * necessary to register every plugin in the pubspec.yaml with a given {@code FlutterEngine}. The
+   * GeneratedPluginRegistrant must be generated per app, because each app uses different sets of
+   * plugins. Therefore, the Android embedding cannot place a compile-time dependency on this
+   * generated class. This method uses reflection to attempt to locate the generated file and then
+   * use it at runtime.
+   *
+   * <p>This method fizzles if the GeneratedPluginRegistrant cannot be found or invoked. This
+   * situation should never occur, but if any eventuality comes up that prevents an app from using
+   * this behavior, that app can still write code that explicitly registers plugins.
+   */
+  private static void registerPlugins(@NonNull FlutterEngine flutterEngine) {
+    try {
+      Class<?> generatedPluginRegistrant =
+          Class.forName("io.flutter.plugins.GeneratedPluginRegistrant");
+      Method registrationMethod =
+          generatedPluginRegistrant.getDeclaredMethod("registerWith", FlutterEngine.class);
+      registrationMethod.invoke(null, flutterEngine);
+    } catch (Exception e) {
+      Log.w(
+          TAG,
+          "Tried to automatically register plugins with FlutterEngine ("
+              + flutterEngine
+              + ") but could not find and invoke the GeneratedPluginRegistrant.");
+    }
+  }
 }