Interacting with native code in Flutter For iOS & Android 

Hello, I’m Alek @MisterAlek github.com/MrAlek CTO @ doneservices.co 

Discount Code FLUTTER300 

Agenda • Flutter under the hood • Why interact with native? • Different ways of interacting with native code • Platform Channel • Dart:ffi (bonus) • Creating a plugin (w/ live coding!) • Considerations & Learnings 

Flutter Internals • Flutter is built with Dart on top of a C++ engine • Does its own drawing with Skia – no platform UI 

No native rendering needed High performance scrolling 60fps animations No bridge hopping when listening to scroll events No drawing / layout bugs between platforms 

Why interact with platform native code? Platform-specific functionality & APIs e.g. Notifications Access hardware e.g. Camera, GPS, Speaker Irreproducible native views (like Maps) Existing libraries, e.g. SQLite, Intercom, Firebase ⛔ Not for drawing / layout, unlike React Native 

Examples 

How do Flutter apps run? • Flutter apps are hosted as frameworks inside native apps • The hosts are regular native apps. • FlutterView (Android) + FlutterViewController (iOS) is the bridge, only one per app. https://flutter.dev/docs/development/platform-integration/platform-channels 

FlutterViewController & FlutterView • Forwards touches, keyboard, lifecycle events • Handles communication with native plugins • Passes messages between Dart and platform native code (Objective-C/Swift/Java/Kotlin) • …using Platform Channels https://flutter.dev/docs/development/platform-integration/platform-channels 

Plugin The thing you get when combining Flutter, iOS & Android code together into a dart package 

pub.dev 

pubspec.yaml 

Creating a plugin • Creates a package with iOS, Android and Dart code • + an example Flutter app for both platforms • Publish with 

Creating a plugin • Creates a package with iOS, Android and Dart code • + an example Flutter app for both platforms • Publish with Android iO S Flutter 

Platform Channels https://flutter.dev/docs/development/platform-integration/platform-channels • Identified by name e.g. ”flutter/lifecycle” • Passes binary messages • Uses a codec for serialization / deserialization • Can both send and receive • Used only on the main thread A simple mechanism for communicating between Dart code and platform code inside a hosted Flutter app. 

BasicMessageChannel 

BasicMessageChannel Swift Kotlin 

Method Channels ✅ • Used to invoke different methods on the same channel to group functionality • Sends a ”method” name and parameters • Uses StandardMessageCodec to parse params & return values https://flutter.dev/docs/development/platform-integration/platform-channels 

MethodChannel 

MethodChannel Swift Kotlin 

Event Channels ✅ • Used to send events over a stream • Example: Listening to device sensors (GPS, Accelerometer, Gyro) • Uses StandardMessageCodec just like method channels 

EventChannel 

Plugin dependencies Your plugins can have dependencies! 1. Other Dart packages (pubspec.yaml) 2. iOS CocoaPods (Podfile) 3. Gradle modules (build.gradle) Common Flutter plugins include SDK wrappers for native 3rd party frameworks • Intercom, Firebase, AWS 

Learnings & Considerations • Use the host app where you run into plugin limitations • Platform channels have built in mocking. Use them for testing • channel.setMockMethodCallHandler • Be wary of Dart types 

Bonus – Dart:ffi • A mechanism for directly calling functions exposed to the C/C++ runtime • Currently in beta (flutter channel dev; flutter upgrade) • Used to interact directly with native frameworks & functions, such as sqlite 

Read more • https://flutter.dev/docs/development/platform-integration/platform-channels • https://github.com/flutter/flutter/ • https://github.com/flutter/plugins/tree/master/packages/battery • https://medium.com/flutter/flutter-platform-channels-ce7f540a104e ”Flutter Platform Channels” by Mikkel Ravn 

Thank you! done. Psst, we’re still hiring @MisterAlek github.com/mralek