Seamless Flutter Native Integration: FFI & Pigeon - Dreamwalker (JaichangPark / 박제창) @FlutterKaigi2024

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Seamless Flutter Native Integration: FFI & Pigeon Dreamwalker (@jaichangpark) 1

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/ Intro Proprietary & Confidential Dreamwalker Park Jai-Chang @jaichangpark @JAICHANGPARK Dreamus Company GDG Golang Korea / Flutter Seoul 2

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Flutter Build for any screen Flutter is an open source framework for building beautiful, natively compiled, multi-platform applications from a single codebase. / overview 3

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/ overview @source: https://dart.dev/overview 4

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AI Artiﬁcial intelligence 6

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AI on a smartphone 7

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AI (On-Device LLM) on a smartphone 8

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@source: https://docs.flutter.dev/resources/architectural-overview 9

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@source: https://docs.flutter.dev/resources/architectural-overview 10

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Platform channels ● Method Channel ○ A named channel for communicating with platform plugins using asynchronous method calls. ● Event Channel ○ A named channel for communicating with platform plugins using event streams. ● Codec ○ A message encoding/decoding mechanism. ■ MessageCodec ■ StandardMessageCodec ■ BinaryCodec ■ JSONMessageCodec ■ StringCodec 11 @source: https://docs.flutter.dev/resources/architectural-overview#integrating-with-other-code

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FlutterActivity package com.dreamwalker.untitled import io.flutter.embedding.android.FlutterActivity class MainActivity: FlutterActivity() 12

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FlutterActivity package com.dreamwalker.untitled import io.flutter.embedding.android.FlutterActivity class MainActivity: FlutterActivity(){ override fun configureFlutterEngine(@NonNull flutterEngine: FlutterEngine) { super.configureFlutterEngine(flutterEngine) // code ... } } 13

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FlutterPlugin import io.flutter.embedding.engine.plugins.FlutterPlugin class CustomFlutterPlugin : FlutterPlugin { override fun onAttachedToEngine(binding: FlutterPlugin.FlutterPluginBinding) { // Initialization and method channel setup for the plugin // code.. } override fun onDetachedFromEngine(binding: FlutterPlugin.FlutterPluginBinding) { methodChannel.setMethodCallHandler(null) } } 14

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FlutterActivity vs FlutterPlugin FlutterActivity FlutterActivity is an Android Activity that displays the Flutter application UI and starts the Flutter engine. You would use FlutterActivity when you want to show Flutter UI within an Android native application. FlutterPlugin FlutterPlugin is an interface for communication between Flutter and the native platform (e.g., Android, iOS). You would implement FlutterPlugin when you want to call native APIs or handle speciﬁc events in a Flutter application. 15

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Platform-Speciﬁc Code Design 16

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/ Platform-Specific Code Design ● plugin_platform_interface ● Pigeon ● FFI(Foreign function interface) → C ● FFIgen ● JNI (Java Native Interface) → Java & Kotlin ● JNIgen (Java Native Interface) ● and other bridges Interoperability 17 Methods : How to

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/ Platform-Specific Code Design Writing a good Flutter plugin 18 ● Think functionality first, then APIs ● Avoid platform-specific API methods ● Avoid supporting only one platform ● Make your plugin easy to navigate and test ● Avoid writing static (or global) methods @sourece : https://medium.com/flutter/writing-a-good-flutter-plugin-1a561b986c9c

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/ Platform-Specific Code Design 1. Requirements Definition 2. Identify required features 3. Data type & structure design 4. Platform code development 5. UI code development Design Checklist 19

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/ Platform-Specific Code 20

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/ Platform-Specific Code Design Channel Name Design Type Detail Channel Name Battery Battery Level MethodChannel com.dreamwalker.flutterkaigi2024/battery ${Common}/battery Battery Charging Status EventChannel com.dreamwalker.flutterkaigi2024/charging Sensor Gyroscope EventChannel com.dreamwalker.flutterkaigi2024/sensors/gyroscope ${Common}/sensors/gyroscope Common package or domain com.dreamwalker.flutterkaigi2024 21

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Common (Flutter, Host(Native)) private val BATT_CHANNEL = "com.dreamwalker.flutterkaigi2024/battery" private val BATT_CHARGING_CHANNEL = "com.dreamwalker.flutterkaigi2024/charging" private val GYROSCOPE_CHANNEL = "com.dreamwalker.flutterkaigi2024/sensors/gyroscope" Host (Native) static const battMethodChannel = MethodChannel('com.dreamwalker.flutterkaigi2024/battery'); static const EventChannel battEventChannel = EventChannel('com.dreamwalker.flutterkaigi2024/charging'); static const EventChannel gyroscopeEventChannel = EventChannel('com.dreamwalker.flutterkaigi2024/sensors/gyroscope); Flutter 22

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/ Platform-Specific Code Design Date Structure & Tpye Design Type Detail Data Type Battery Battery Level INT Sensor Gyroscope X Double Gyroscope Y Double Gyroscope Z Double Gyroscope List 23

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/ Platform-Specific Code Design 24

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Host (Native) - Android / Kotlin MethodChannel( flutterEngine.dartExecutor.binaryMessenger, BATT_CHANNEL, ).setMethodCallHandler { call, result -> if (call.method == "getBatteryLevel") { CoroutineScope(Dispatchers.Main).launch { val batteryLevel = getBatteryLevel() if (batteryLevel != -1) { result.success(batteryLevel) } else { result.error("UNAVAILABLE", "Battery level not available.", null) } } } else { result.notImplemented() } } 25

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● Conﬁgures, bootstraps, and starts executing Dart code. ● Once started, a DartExecutor cannot be stopped. The associated Dart code will execute until it completes, or until the FlutterEngine that owns this DartExecutor is destroyed. ● Creates a FlutterEngine in this group and run its DartExecutor with a default entrypoint of the "main" function in the "lib/main.dart" ﬁle. DartExecutor 27

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Host (Native) - Android / Kotlin class SensorPlugin : FlutterPlugin { override fun onAttachedToEngine(binding: FlutterPlugin.FlutterPluginBinding) { val sensorsManager = binding.applicationContext.getSystemService(Context.SENSOR_SERVICE) as SensorManager gyroscopeChannel = EventChannel(binding.binaryMessenger, GYROSCOPE_CHANNEL) gyroscopeChannel.setStreamHandler(object : EventChannel.StreamHandler { override fun onListen(arguments: Any?, events: EventSink?) { } override fun onCancel(arguments: Any?) { } }) } 32

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Host (Native) - Android / Kotlin FlutterPlugin private fun sensorEventListener(events: EventChannel.EventSink): SensorEventListener { return object : SensorEventListener { override fun onAccuracyChanged(sensor: Sensor, accuracy: Int) {} override fun onSensorChanged(event: SensorEvent) { val sensorValues = DoubleArray(event.values.size) event.values.forEachIndexed { index, value -> sensorValues[index] = value.toDouble() } events.success(sensorValues) } } } 37

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Host (Native) - Android / Kotlin class MainActivity : FlutterActivity() { override fun configureFlutterEngine(@NonNull flutterEngine: FlutterEngine) { super.configureFlutterEngine(flutterEngine) flutterEngine.plugins.add(SensorPlugin()) MethodChannel( flutterEngine.dartExecutor.binaryMessenger, CHANNEL, ).setMethodCallHandler { call, result -> // code .. } } } You can easily add other Flutter plugins 40

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Flutter : MethodChannel 41 Future getBatteryLevel() async { String batteryLevel; try { final result = await platform.invokeMethod('getBatteryLevel'); batteryLevel = 'Battery level at $result % .'; } on PlatformException catch (e) { batteryLevel = "Failed to get battery level: '${e.message}'."; } setState(() { // code.. }); } method channel

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Flutter : MethodChannel 42 Future getBatteryLevel() async { String batteryLevel; try { final result = await platform.invokeMethod('getBatteryLevel'); batteryLevel = 'Battery level at $result % .'; } on PlatformException catch (e) { batteryLevel = "Failed to get battery level: '${e.message}'."; } setState(() { // code.. }); } int int?

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Flutter : MethodChannel 43 Future getBatteryLevel() async { String batteryLevel; try { final result = await platform.invokeMethod('getBatteryLevel'); batteryLevel = 'Battery level at $result % .'; } on PlatformException catch (e) { batteryLevel = "Failed to get battery level: '${e.message}'."; } setState(() { // code.. }); } dynamic

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Flutter : EventChannel 44 Stream? gyroscopeEvents; static const EventChannel gyroscopeEventChannel = EventChannel('com.xxx.xxx/sensors/gyroscope'); gyroscopeEvents ??= gyroscopeEventChannel.receiveBroadcastStream().map((dynamic event) { final list = event.cast(); return GyroscopeEventData( list[0]!, list[1]!, list[2]! ); });

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Flutter : EventChannel 45 Stream? gyroscopeEvents; static const EventChannel gyroscopeEventChannel = EventChannel('com.xxx.xxx/sensors/gyroscope'); gyroscopeEvents ??= gyroscopeEventChannel.receiveBroadcastStream().map((dynamic event) { final list = event.cast(); return GyroscopeEventData( list[0]!, list[1]!, list[2]! ); });

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/ Platform-Specific Code Design Platform-Specific Pattern 01 46

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/ Platform-Specific Code Design Platform-Specific Pattern 02 47

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/ Platform-Specific Code Design Platform-Specific Pattern 03 48

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/ Platform-Specific Code Design Platform-Specific Pattern 04 49

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/ Platform-Specific Code Design Platform-Specific Pattern 05 50 plugin_platform_interface

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/ Platform-Specific Code Design Platform-Specific Pattern 05 51

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/ Platform-Specific Code Design Platform-Specific Pattern 05 52

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53 @source: https://pub.dev/packages/plugin_platform_interface

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type-safe? 54

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/ Pigeon type-safe? 55

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/ Pigeon type-safe? 56 Protocol Buﬀers & JSON

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@jaichangpark, shots on iPhone in Shinjuku Pigeon ハト 57

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Pigeon is a code generator tool to make communication between Flutter and the host platform type-safe, easier, and faster. ● Pigeon removes the necessity to manage strings across multiple platforms and languages. ● It also improves eﬃciency over common method channel patterns. ● Most importantly though, it removes the need to write custom platform channel code, since pigeon generates it for you. Code generator tool Pigeon 58

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Currently pigeon supports generating: ● Kotlin and Java code for Android ● Swift and Objective-C code for iOS and macOS ● C++ code for Windows ● GObject code for Linux Supported Platforms Pigeon 59

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60 @Source ● https://pub.dev/packages/pigeon ● https://github.com/flutter/packages/tree/ main/packages/pigeon ● Access Date: 2024.10

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ﬂutter packages Use Cases 61 ● shared_preferences ● url_launcher ● image_picker ● camera ● in_app_purchase ● video_player ● and so on / Pigeon

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Flutterﬁre Use Cases 62 @source: https://github.com/firebase/flutterfire/pull/8921 from 2022.06~ / Pigeon

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Pigeon 63 Code generator tool

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Mission 64 / Pigeon

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1. Installing Add pigeon as a dev_dependency 65

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66 enum AlgorithmType { sha1, sha2, md5, aesCbc, aesEcb, } class MessageData { MessageData({required this.type, required this.data}); AlgorithmType type; String? data; } 2. Deﬁne Messages

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67 @HostApi() abstract class CustomHostApi { String generateHash(MessageData message); String encrypt(MessageData message); @async String decrypt(MessageData message); } 3. Deﬁne APIs

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@HostApi ● @HostApi() being for procedures that are defined on the host platform. ● When you want to call the host platform from Flutter. @FlutterApi ● @FlutterApi() for procedures that are defined in Dart. ● When you want to call a Flutter app from the host platform. 68 / Pigeon

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69 4. Code Generation dart run pigeon \ --input pigeons/messaging.dart \ --dart_out lib/pigeon.dart \ --objc_header_out ios/Runner/pigeon.h \ --objc_source_out ios/Runner/pigeon.m \ --java_out ./android/app/src/main/java/com/example/xxxx/Pigeon.java \ --java_package "com.example.xxxx"

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70 @ConfigurePigeon(PigeonOptions( dartOut: 'lib/src/messages.g.dart', dartOptions: DartOptions(), cppOptions: CppOptions(namespace: 'flutter_pigeon'), cppHeaderOut: 'windows/runner/messages.g.h', cppSourceOut: 'windows/runner/messages.g.cpp', kotlinOut: 'android/app/src/main/kotlin/com/dreamwalker/flutter_pigeon/Messages.g.kt', kotlinOptions: KotlinOptions(), javaOut: 'android/app/src/main/java/io/flutter/plugins/Messages.java', javaOptions: JavaOptions(), swiftOut: 'ios/Runner/Messages.g.swift', swiftOptions: SwiftOptions(), objcHeaderOut: 'macos/Runner/messages.g.h', objcSourceOut: 'macos/Runner/messages.g.m', objcOptions: ObjcOptions(prefix: 'PGN'), copyrightHeader: 'pigeons/copyright.txt', dartPackageName: 'flutter_pigeon', )) 4. Code Generation message.dart

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71 @ConfigurePigeon(PigeonOptions( dartOut: 'lib/src/messages.g.dart', dartOptions: DartOptions(), cppOptions: CppOptions(namespace: 'flutter_pigeon'), cppHeaderOut: 'windows/runner/messages.g.h', cppSourceOut: 'windows/runner/messages.g.cpp', kotlinOut: 'android/app/src/main/kotlin/com/dreamwalker/flutter_pigeon/Messages.g.kt', kotlinOptions: KotlinOptions(), javaOut: 'android/app/src/main/java/io/flutter/plugins/Messages.java', javaOptions: JavaOptions(), swiftOut: 'ios/Runner/Messages.g.swift', swiftOptions: SwiftOptions(), objcHeaderOut: 'macos/Runner/messages.g.h', objcSourceOut: 'macos/Runner/messages.g.m', objcOptions: ObjcOptions(prefix: 'PGN'), copyrightHeader: 'pigeons/copyright.txt', dartPackageName: 'flutter_pigeon', ))

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72 @ConfigurePigeon(PigeonOptions( dartOut: 'lib/src/messages.g.dart', dartOptions: DartOptions(), cppOptions: CppOptions(namespace: 'flutter_pigeon'), cppHeaderOut: 'windows/runner/messages.g.h', cppSourceOut: 'windows/runner/messages.g.cpp', kotlinOut: 'android/app/src/main/kotlin/com/dreamwalker/flutter_pigeon/Messages.g.kt', kotlinOptions: KotlinOptions(), javaOut: 'android/app/src/main/java/io/flutter/plugins/Messages.java', javaOptions: JavaOptions(), swiftOut: 'ios/Runner/Messages.g.swift', swiftOptions: SwiftOptions(), objcHeaderOut: 'macos/Runner/messages.g.h', objcSourceOut: 'macos/Runner/messages.g.m', objcOptions: ObjcOptions(prefix: 'PGN'), copyrightHeader: 'pigeons/copyright.txt', dartPackageName: 'flutter_pigeon', )) com.dreamwalker.flutter_pigeon

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73 @ConfigurePigeon(PigeonOptions( dartOut: 'lib/src/messages.g.dart', dartOptions: DartOptions(), cppOptions: CppOptions(namespace: 'flutter_pigeon'), cppHeaderOut: 'windows/runner/messages.g.h', cppSourceOut: 'windows/runner/messages.g.cpp', kotlinOut: 'android/app/src/main/kotlin/com/dreamwalker/flutter_pigeon/Messages.g.kt', kotlinOptions: KotlinOptions(), javaOut: 'android/app/src/main/java/io/flutter/plugins/Messages.java', javaOptions: JavaOptions(), swiftOut: 'ios/Runner/Messages.g.swift', swiftOptions: SwiftOptions(), objcHeaderOut: 'macos/Runner/messages.g.h', objcSourceOut: 'macos/Runner/messages.g.m', objcOptions: ObjcOptions(prefix: 'PGN'), copyrightHeader: 'pigeons/copyright.txt', dartPackageName: 'flutter_pigeon', ))

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dart run pigeon --input ./pigeons/message.dart 74

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75 / Pigeon Folder Structure

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76 final CustomHostApi _api = CustomHostApi(); Future genSha2(String input) async { try { final v = await _api.generateHash( MessageData(type: AlgorithmType.sha2, data: input), ); } catch (e) { return "$e"; } } 5. Flutter Side

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77 private class CustomApiImpl : CustomHostApi { override fun generateHash(message: MessageData): String { //code... } override fun encrypt(message: MessageData): String { TODO("Not yet implemented") } override fun decrypt(message: MessageData, callback: (Result) -> Unit) { TODO("Not yet implemented") } } 5. Android (Kotlin) CustomHostApi: Generated Code by pigeon

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78 private class CustomApiImpl : CustomHostApi { override fun generateHash(message: MessageData): String { //code... } override fun encrypt(message: MessageData): String { TODO("Not yet implemented") } override fun decrypt(message: MessageData, callback: (Result) -> Unit) { TODO("Not yet implemented") } } 5. Android (Kotlin) @async

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79 class MainActivity : FlutterActivity() { override fun configureFlutterEngine(flutterEngine: FlutterEngine) { super.configureFlutterEngine(flutterEngine) val api = CustomApiImplementation() CustomHostApi.setUp(flutterEngine.dartExecutor.binaryMessenger, api) } } 5. Android (Kotlin)

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80 / Pigeon

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81 / Pigeon Oops!

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82 private class CustomApiImpl: CustomHostApi { func generateHash(message: MessageData) throws -> String { } func encrypt(message: MessageData) throws -> String { } func decrypt(message: MessageData, completion: @escaping (Result) -> Void) { } } 5. iOS (swift) Using CryptoKit

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83 @main @objc class AppDelegate: FlutterAppDelegate { override func application( _ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]? ) -> Bool { GeneratedPluginRegistrant.register(with: self) let controller = window?.rootViewController as! FlutterViewController let api = CustomApiImpl() CustomHostApiSetup.setUp(binaryMessenger: controller.binaryMessenger, api: api) return super.application(application, didFinishLaunchingWithOptions: launchOptions) } } 5. iOS (swift)

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84 / Pigeon

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Foreign Function Interface ﬃ 85

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86 / Foreign Function Interface ● FFI stands for foreign function interface. ● Dart mobile, command-line, and server apps running on the Dart Native platform can use the dart:ffi library to call native C APIs, and to read, write, allocate, and deallocate native memory. ● ffigen only supports parsing C headers, not C++ headers.

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87 / Foreign Function Interface ● Databases ● Graphic & Image processing ● OS (Native) API → Windows, Linux etc. ● C-based compiled libs

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88 / Foreign Function Interface

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89 ﬁbonacci #ifndef FIBONACCI_H #define FIBONACCI_H int fibonacci(int n); #endif // FIBONACCI_H ﬁbonacci.h @Source https://en.wikipedia.org/wiki/Fibonacci_sequence By Romain - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=114415511

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90 ﬁbonacci int fibonacci(int n) { if (n <= 0) { return 0; } else if (n == 1) { return 1; } else { return fibonacci(n - 1) + fibonacci(n - 2); } } ﬁbonacci.c

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91 ﬁbonacci cmake_minimum_required(VERSION 3.10) project(FibonacciLibrary) include_directories(include) add_library(fibonacci SHARED fibonacci.c) add_executable(fibonacci_app fibonacci.c) target_link_libraries(fibonacci_app fibonacci) CMakeList.txt

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92 ﬁbonacci main.dart var libraryPath = path.join(Directory.current.path, 'lib/fibonacci', 'libfibonacci.dylib'); final dylib = ffi.DynamicLibrary.open(libraryPath);

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93 ! Key Point final DynamicLibrary _dylib = () { if (Platform.isMacOS || Platform.isIOS) { return DynamicLibrary.open('$_libName.framework/$_libName'); } if (Platform.isAndroid || Platform.isLinux) { return DynamicLibrary.open('lib$_libName.so'); } if (Platform.isWindows) { return DynamicLibrary.open('$_libName.dll'); } throw UnsupportedError('Unknown platform: ${Platform.operatingSystem}'); }();

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94 ﬁbonacci main.dart final fibo = dylib .lookup>('fibonacci') .asFunction(); lib(Native) Function Client (Dart) Function function name Data Type of parameters Return Data Type

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95 / Foreign Function Interface ● Rust Programming Language ● Go Programming Language

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96 / Foreign Function Interface

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97 #[no_mangle] pub extern "C" fn fibonacci(n: i32) -> i32 { if n <= 0 { return 0; } else if n == 1 { return 1; } else { let mut a = 0; let mut b = 1; let mut c = 0; for _ in 2..=n { c = a + b; a = b; b = c; } return c; } cargo build --release --target=[target] Android cargo ndk -t [target] -o ./jniLibs build --release ● arm64-v8a ● armeabi-v7a ● x86 ● x86_64

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99 _dylib = () { if (Platform.isAndroid || Platform.isLinux) { return ffi.DynamicLibrary.open('librust_lib.so'); } throw UnsupportedError('Unknown platform: ${Platform.operatingSystem}'); }();

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100 typedef FibonacciFunc = ffi.Int Function(ffi.Int); typedef Fibonacci = int Function(int); final Fibonacci fibonacci = _dylib .lookup>('fibonacci') .asFunction(); int n = 10; int result = fibonacci(n);

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101 / Foreign Function Interface Generator for FFI bindings, using LibClang to parse C, Objective-C, and Swift ﬁles. ﬃgen

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ﬃgen Add ﬃgen as a dev_dependency 102

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103 ﬃgen name: NativeLibrary description: misc output: 'generated_bindings.dart' headers: entry-points: - 'lib/fibonacci/fibonacci.h' include-directives: - 'lib/fibonacci/fibonacci.h' ﬃgen.yaml Class Name

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104 ﬃgen dart run ffigen --config ffigen.yaml

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105 ﬃgen NativeLibrary nativeLibrary = NativeLibrary(dylib); print(nativeLibrary.fibonacci(10)); Generated a Class Using ﬃgen

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106 / Summary ● Platform-Specific Code ○ Method Channel, Event Channel ○ plugin_platform_interface ○ ffi, ffigen, jnigen, pigeon, etc. ● Pigeon ○ Code generator tool ○ type-safe ● FFI ○ FFI stands for foreign function interface. ○ Lookup, asFunction ○ ffigen

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Thank You ご清聴ありがとうございました Flutter Seoul GDG Golang Korea Dreamwalker (@jaichangpark) 107