Fast Prototypes with Flutter + Kotlin/Native JB Lorenzo OLX Group, Berlin 

we fuel local economies by making it super easy for anyone to buy or sell almost anything through our platforms Our Mission 

Who We Are we operate a network of market-leading trading platforms in over 40 countries that are used by more than 350 million people every month to buy and sell almost anything 

Our Numbers brands 17 + people 500 0+ daily listings 1M + offices 35 daily events 4B + daily notifications 50M + monthly users 350M + countries 43 shopping app (20+ markets) #1 

The Story OLX P&Tech Conference App The Team 

The Story 

Outline: - Why? - How? (to Setup) - How? (to use it) - What? (pitfalls, considerations) 

Why Flutter + Kotlin/Native 

Architecture 

How do I start What project structure works? 

What project structure works? - Kotlin/Native_version = ‘0.8.2’ - kotlin_version = ‘1.2.31' - flutter: sdk: flutter - google_sign_in: 3.0.5 - url_launcher: ^3.0.3 - device_calendar: 0.0.6 

Flutter project structure 

settings.gradle Flutter project structure How do I + Kotlin/Native 

settings.gradle Flutter project structure Kotlin/Native 

// settings.gradle include ':app' def flutterProjectRoot =rootProject.projectDir.parentFile.toPath() def plugins =new Properties() def pluginsFile =new File(flutterProjectRoot.toFile(), '.flutter-plugins') if (pluginsFile.exists()) { pluginsFile.withReader('UTF-8') { reader -> plugins.load(reader) } } plugins.each { name, path -> def pluginDirectory=flutterProjectRoot.resolve(path).resolve('android').toFile() include":$name" project(":$name").projectDir =pluginDirectory } 

// settings.gradle include ':app' // ... some flutter directives include ':common' includė ':ios' project(":ios").projectDir = new File("ios") project(":common").projectDir = new File("common") 

// android/build.gradle rootProject.buildDir = '../build' subprojects { project.buildDir = "${rootProject.buildDir}/${project.name}" } 

// ios/build.gradle buildscript { // ... kotlin-native classpath and repositories } apply plugin: 'konan' konan.targets = ['iphone', 'iphone_sim'] konanArtifacts { framework('YourFrameworkName') { enableMultiplatform true } } dependencies { expectedBy project(':common') } 

// common/build.gradle // ... kotlin-gradle classpath apply plugin: 'kotlin-platform-common' group = 'com.olxgroup.olxconf' // ... repositories dependencies { compile "org.jetbrains.kotlin:kotlin-stdlib-common: $kotlin_version" } 

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Now we've setup - settings.gradle - android/build.gradle - ios/build.gradle - common/build.gradle - framework in iOS 

* For Glueing code 

Now we can start coding in Flutter + Kotlin/Native ... How to use it? 

iOS // AppDelegate.swift import YourFrameworkName // from Kotlin-Native // ... let channel = FlutterMethodChannel.init(name: "/channel", binaryMessenger: controller) channel.setMethodCallHandler({(call: FlutterMethodCall, result: @escaping FlutterResult) -> Void in // Process call.method and result }); GeneratedPluginRegistrant.register(with: self) 

Android // MainActivity.kt GeneratedPluginRegistrant.registerWith(this) MethodChannel(flutterView, CHANNEL).setMethodCallHandler { call, result -> when (call.method) { "methodName" -> doSomethingWith(result) } } 

Pitfalls * Packing and Unpacking (Object passing into FlutterChannel) * Kotlin Companion objects in Swift * Kotlin-Native version dependent support (e.g. for arm32) * Kotlin-Native without JVM is not typical (missing standard libraries, e.g. url parsing) 

The Result 

Takeaways * Flutter is awesome for fast prototypes * Flutter and Kotlin/Native are still in beta but is usable already though with some limitations * Kotlin/Native works well to reduce the amount of platform specific code * Some glue code needs to be written to pass around/ serialize objects * Don’t be afraid to try out new technologies (but …) 

THANK YOU! Questions? Get in touch with us olxgroup.com tech.olx.com olxtechberlin [email protected] jblorenzo