AppController.kt

class AppController : Application() {

    lateinit var engine: FlutterEngine

    override fun onCreate() {
        super.onCreate()

        // Instantiate a FlutterEngine.
        engine = FlutterEngine(this)

        // Start executing Dart code to pre-warm the FlutterEngine.
        engine.dartExecutor.executeDartEntrypoint(
                DartExecutor.DartEntrypoint.createDefault()
        )

        // Cache the FlutterEngine to be used by FlutterActivity.
        FlutterEngineCache
                .getInstance()
                .put("my_engine_id", engine)

    }
}