Using native code in a Flutter application is done through Platform Channels, FFI, or Platform Plugins. Below is a clear, step-by-step guide explaining all approaches.

✅ 1. Using Platform Channels (Most Common Way)

Use MethodChannel in Flutter to communicate with Kotlin/Java (Android) and Swift/Objective-C (iOS).

🔹 Step 1: Create a MethodChannel in Flutter

import 'package:flutter/services.dart';

class NativeHelper {
  static const platform = MethodChannel('com.example/native');

  static Future<String> getNativeMessage() async {
    final message = await platform.invokeMethod('getMessage');
    return message;
  }
}

🔹 Step 2: Call Native Method from Flutter

ElevatedButton(
  onPressed: () async {
    final msg = await NativeHelper.getNativeMessage();
    print(msg);
  },
  child: Text("Call Native Code"),
)

✅ 2. Add Native Code in Android (Kotlin/Java)

Android → Kotlin Example

Path: android/app/src/main/kotlin/.../MainActivity.kt

package com.example.nativecode

import io.flutter.embedding.android.FlutterActivity
import io.flutter.embedding.engine.FlutterEngine
import io.flutter.plugin.common.MethodChannel

class MainActivity: FlutterActivity() {

    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
        super.configureFlutterEngine(flutterEngine)

        MethodChannel(flutterEngine.dartExecutor.binaryMessenger, "com.example/native")
            .setMethodCallHandler { call, result ->
                if (call.method == "getMessage") {
                    result.success("Hello from Android Native Code!")
                } else {
                    result.notImplemented()
                }
            }
    }
}

✅ 3. Add Native Code in iOS (Swift)

Path: ios/Runner/AppDelegate.swift

import UIKit
import Flutter

@UIApplicationMain
class AppDelegate: FlutterAppDelegate {

  override func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
  ) -> Bool {

    let controller = window?.rootViewController as! FlutterViewController
    let channel = FlutterMethodChannel(name: "com.example/native", binaryMessenger: controller.binaryMessenger)

    channel.setMethodCallHandler { (call, result) in
        if call.method == "getMessage" {
            result("Hello from iOS Native Code!")
        } else {
            result(FlutterMethodNotImplemented)
        }
    }

    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
  }
}

🎉 Output

When Flutter calls getNativeMessage():

• Android returns → “Hello from Android Native Code!”
• iOS returns → “Hello from iOS Native Code!”

✅ 4. Using FFI (Dart → C/C++ native code)

Use when performance is critical (like encryption, video processing, audio processing).

Example structure:

/flutter_project
  /native_lib
    - mylib.c

Dart side:

import 'dart:ffi';
import 'dart:io';

typedef NativeAddFunc = Int32 Function(Int32, Int32);
typedef AddFunc = int Function(int, int);

final dylib = Platform.isAndroid
    ? DynamicLibrary.open('libmylib.so')
    : DynamicLibrary.process();

final addPointer = dylib.lookup<NativeFunction<NativeAddFunc>>('add');
final add = addPointer.asFunction<AddFunc>();

void main() {
  print(add(10, 20)); // prints 30
}

✅ 5. Create a Flutter Plugin (Reusable native code)

Use when your native feature will be reused in multiple apps.

flutter create --template=plugin my_native_plugin

This scaffolds native code folders for Android & iOS.

📌 Summary Table