how to create a native bridge between flutter and android

Introduction

We will look at how to create a native bridge between Flutter and Android Native (Kotlin) in this article. I will make this brief and straight to the point.

It should be noted that this bridge will transfer integer data from Flutter to Android and string data from Android to Flutter, but you can use this to transfer other data as well.

Building Native Bridge

One-way communication

Build a native bridge in Flutter
1. Add services.dart import
```
 import 'package:flutter/services.dart';
```
2. Add NativeBridge class
```
 class NativeBridge {
   static const MethodChannel _channel = MethodChannel('com.example/native');

   static void getNativeData() async {
     await _channel.invokeMethod('getNativeData').then((value) => print(value));
   }
 }
```
  First, we are going to create a NativeBridge class in which we will write our connection code. The bridge in the native code will be identified by the same name that we are using to create a static MethodChannel. The getNativeData method in our Kotlin file will be called by the static method getNativeData(), which will then print the log statement.
3. Call getNativeData() method
```
 NativeBridge.getNativeData();
```
  Call the static method getNativeData() anywhere sensible in your Dart code.

Connect it's counterpart in MainActivity.kt

Add necessary imports

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

Add this code snippet to MainActivity class

 private val CHANNEL = "com.example/native"

     override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
         super.configureFlutterEngine(flutterEngine)
         MethodChannel(flutterEngine.dartExecutor.binaryMessenger, CHANNEL).setMethodCallHandler {
             call, result ->
             if (call.method == "getNativeData") {
                 val data = getNativeData()
                 result.success(data)
             } else {
                 result.notImplemented()
             }
         }
     }

     private fun getNativeData(): String {
         // Implement your native code logic here
         return "Native Data from Android"
     }

The CHANNEL name in this case needs to match the MethodChannel name in our dart file in order to connect the two channels. For the purpose of determining which method to execute, we now write a simple if-check statement and then execute the required method.

Final code files for one-way communication between Flutter and Android

main.dart

  // ignore_for_file: avoid_print

  import 'package:flutter/material.dart';
  import 'package:flutter/services.dart';

  void main() => runApp(const MyApp());

  class MyApp extends StatelessWidget {
    const MyApp({super.key});

    @override
    Widget build(BuildContext context) {
      return MaterialApp(
        title: 'My App',
        theme: ThemeData(
          colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
          useMaterial3: true,
        ),
        home: const HomePage(),
      );
    }
  }

  class NativeBridge {
    static const MethodChannel _channel = MethodChannel('com.example/native');

    static void getNativeData() async {
      await _channel.invokeMethod('getNativeData').then((value) => print(value));
    }
  }

  class HomePage extends StatelessWidget {
    const HomePage({super.key});

    @override
    Widget build(BuildContext context) {
      NativeBridge.getNativeData();

      return Scaffold(
        appBar: AppBar(
          backgroundColor: Theme.of(context).colorScheme.inversePrimary,
          title: const Text('My App'),
        ),
        body: const Center(
          child: Text('data'),
        ),
      );
    }
  }

MainActivity.kt

  package com.example.bridge

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

  class MainActivity: FlutterActivity() {
      private val CHANNEL = "com.example/native"

      override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
          super.configureFlutterEngine(flutterEngine)
          MethodChannel(flutterEngine.dartExecutor.binaryMessenger, CHANNEL).setMethodCallHandler {
              call, result ->
              if (call.method == "getNativeData") {
                  val data = getNativeData()
                  result.success(data)
              } else {
                  result.notImplemented()
              }
          }
      }

      private fun getNativeData(): String {
          // Implement your native code logic here
          return "Native Data from Android"
      }
  }

Here, we have managed to successfully create a one-way connection between Android and Flutter. In this case, a log statement stating "Native Data from Android," which is coming from Android to Flutter, is printed when the app runs.

Two-way communication

Two-way communication can be achieved by adding a few data type parameters to _channel.invokeMethod and making minor adjustments to getNativeData method. The finished Dart and Kotlin files are below.

main.dart

  // ignore_for_file: avoid_print

  import 'package:flutter/material.dart';
  import 'package:flutter/services.dart';

  void main() => runApp(const MyApp());

  class MyApp extends StatelessWidget {
    const MyApp({super.key});

    @override
    Widget build(BuildContext context) {
      return MaterialApp(
        title: 'My App',
        theme: ThemeData(
          colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
          useMaterial3: true,
        ),
        home: const HomePage(),
      );
    }
  }

  class NativeBridge {
    static const MethodChannel _channel = MethodChannel('com.example/native');

    static void getNativeData(int num) async {
      await _channel.invokeMethod('getNativeData', <String, int>{
        "num": num,
      }).then((value) => print(value));
    }
  }

  class HomePage extends StatelessWidget {
    const HomePage({super.key});

    @override
    Widget build(BuildContext context) {
      int i = 0;

      return Scaffold(
        appBar: AppBar(
          backgroundColor: Theme.of(context).colorScheme.inversePrimary,
          title: const Text('My App'),
        ),
        body: Center(
          child: ElevatedButton(
            onPressed: () {
              NativeBridge.getNativeData(++i);
            },
            child: const Text('Click me'),
          ),
        ),
      );
    }
  }

MainActivity.kt

  package com.example.bridge

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

  class MainActivity: FlutterActivity() {
      private val CHANNEL = "com.example/native"

      override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
          super.configureFlutterEngine(flutterEngine)
          MethodChannel(flutterEngine.dartExecutor.binaryMessenger, CHANNEL).setMethodCallHandler {
              call, result ->
              if (call.method == "getNativeData") {
                  if (!call.hasArgument("num")) {
                      result.error("MissingArgumentError", "You must provide num parameter", null)
                  }
                  val num: Int = call.argument<Int>("num")!!
                  val data = getNativeData(num)
                  result.success(data)
              } else {
                  result.notImplemented()
              }
          }
      }

      private fun getNativeData(num: Int): String {
          // Implement your native code logic here
          return "From Native: $num"
      }
  }

Here, we have successfully created a two-way communication channel between Flutter and Android. When we click the on-screen button, we send integer data to Android and receive a different string each time (in the form of a log statement).

The complete project source code for the one-way and two-way communication codes is maintained commit-wise; you can view it by clicking this link.

Thank you

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Feel free to connect with me. 👋

Native Bridge between Flutter and Android

Establishing two-way communication in Flutter

Table of contents

Introduction

Building Native Bridge

One-way communication

Two-way communication

Thank you