flutter/docs/wiki_archive/Experimental-Use-old-plugins-with-new-embedding.md

Flutter's v2 Android embedding includes reflection code that should find and register all plugins listed in your pubspec.yaml file without any intervention on your part. If your desired plugins are not registered automatically, please file an issue.

Partial plugin registration

To prevent Flutter from registering all plugins and instead register only specific plugins of your choosing, do the following.

First, construct a FlutterEngine either as a cached FlutterEngine, or by overriding provideFlutterEngine() in FlutterActivity or FlutterFragment such that the FlutterEngine instance doesn't automatically register plugins.

FlutterEngine flutterEngine = new FlutterEngine(
  context,
  FlutterLoader.getInstance(),
  new FlutterJNI(),
  dartVmArgs, // or an empty array if no args needed
  false // this arg instructs the FlutterEngine NOT to register plugins automatically
);

Second, register the plugins that you want. If you overrode provideFlutterEngine() in FlutterActivity or FlutterFragment then override configureFlutterEngine() to add plugins:

public void configureFlutterEngine(FlutterEngine engine) {
  // The ShimPluginRegistry is how the v2 embedding works with v1 plugins.
  ShimPluginRegistry shimPluginRegistry = new ShimPluginRegistry(
    flutterEngine,
    new PlatformViewsController()
  );

  // Add any v1 plugins to the shim
  // MyV1Plugin.registerWith(
  //   shimPluginRegistry.registrarFor("com.my.package.MyV1Plugin")
  // );

  // Add any v2 plugins that you want
  // engine.getPlugins().add(new MyPlugin());
}

If you went with the cached FlutterEngine approach instead of FlutterActivity and FlutterFragment method overrides, then you can add plugins whenever you'd like. You can even add them immediately after instantiating your FlutterEngine. However, be advised that some v1 plugins expect an Activity to be available immediately upon registration. This will not be the case unless you add plugins in configureFlutterEngine() as shown earlier.

// Instantiate cached FlutterEngine.
FlutterEngine flutterEngine = new FlutterEngine(
  context,
  FlutterLoader.getInstance(),
  new FlutterJNI(),
  dartVmArgs, // or an empty array if no args needed
  false // this arg instructs the FlutterEngine NOT to register plugins automatically
);

// Immediately add plugins to the cached FlutterEngine.
// The ShimPluginRegistry is how the v2 embedding works with v1 plugins.
ShimPluginRegistry shimPluginRegistry = new ShimPluginRegistry(
  flutterEngine,
  new PlatformViewsController()
);

// Add any v1 plugins to the shim
// MyV1Plugin.registerWith(
//   shimPluginRegistry.registrarFor("com.my.package.MyV1Plugin")
// );

// Add any v2 plugins that you want
// engine.getPlugins().add(new MyPlugin());