How to communicate with native code from flutter?

AppDelegate.swift

/// iOS Swift Code

import Flutter

let CHANNEL = "com.example.native_calls"

class ViewController: UIViewController {
  override func viewDidLoad() {
    super.viewDidLoad()

    let methodChannel = FlutterMethodChannel(name: CHANNEL, binaryMessenger: self.binaryMessenger)
    methodChannel.setMethodCallHandler({ [weak self] (call: FlutterMethodCall, result: FlutterResult) -> Void in
        guard call.method == "getNativeString" else {
            result(FlutterMethodNotImplemented)
            return
        }

        let nativeString = "Hello from native code!"
        result(nativeString)
    })
  }
}

flutter_native_communication.dart

/// Flutter Code

import 'package:flutter/services.dart';

final platform = MethodChannel('com.example.native_calls');

Future<String> getNativeString() async {
  String result = await platform.invokeMethod('getNativeString');
  return result;
}

MainActivity.kt

/// Android Code

class MainActivity: FlutterActivity() {
    private val CHANNEL = "com.example.native_calls"
  
    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
        super.configureFlutterEngine(flutterEngine)
        MethodChannel(flutterEngine.dartExecutor.binaryMessenger, CHANNEL).setMethodCallHandler {
            call, result ->
            if (call.method == "getNativeString") {
                val nativeString = "Hello from native code!"
                result.success(nativeString)
            } else {
                result.notImplemented()
            }
        }
    }
}