Flutter + Kotlin Multiplatform = Klutter

Having worked with Flutter I can say I really like it. Dart was a breeze to learn coming from Java. Hot reload is the best thing since sliced bread, writing a native looking and feeling UI for iOS and Android once is a godsend and the speed with which you can churn out an MVP is ridiculous. While Flutter can be a bit too verbose to my liking, it still is a nice declarative way of building a UI.

Yet after a year I still decided to move to Kotlin Multiplatform. Why? For starters, I have to say dependency management in Flutter/Dart is not very good. Once you start making something a bit more complex than a simple MVP, you probably want to start using native functionality. As an efficient (lazy?) developer you will first check if there are libraries available. Using one or two of them is fine, but keep adding more, and soon you will get caught in a dependency nightmare. In this regard Kotlin Multiplatform is not all that much better, mostly because of the lack of available libraries.

However, that’s much less of an issue in KMP than it is in Flutter. If you’re focussed on Flutter you will be using Dart as a programming language. When you want to use native functionality you can either choose to use 3rd party libraries (which can be a bad choice as said above) or you can write the native code yourselves. Doing that means writing code in Kotlin or Java for Android and in Objective-C or Swift for iOS. So if you want to be in full control of your app and write as much as possible yourself then you have no other option than to write in 3 different programming languages. When using KMP you can use Kotlin for both Android and iOS native functionality, making it a lot more accessible.

These points are relevant for the backend code but looking at the frontend things are a little different. In contrast to what is discussed above, Flutter is a lot more accessible for frontend development than Kotlin Multiplatform. Both Flutter and KMP can create native (looking/feeling) UI. With Flutter, you will however only have to do this once. Using KMP you will have to create a UI with Kotlin for Android and for iOS with Swift. Now Kotlin and Swift are very similar programming languages, so it won’t be hard for a Kotlin programmer to start using Swift. A very nice comparison can be read on https://www.raywenderlich.com.

Kotlin and Swift might be very similar, but it does not take away the fact you will have to write code twice instead of once. I initially chose to work with Flutter because I did not want to write a UI twice so was I really going to do this? I created a little MVP with KMP, but I was not convinced this was the way. I don’t want to write a UI twice. I don’t want to write backend code twice. I got Flutter… I got KMP. Why not use both? Why not use both? And that’s when I stated. on Klutter. I did a POC manually hooking up a KMP library into a Flutter app and after a few headaches it worked. At first, I wanted to publish a template to create a Flutter + KMP app from scratch. Since then, it has evolved to a little framework consisting of annotations, a Gradle plugin and a Pub plugin. Curious?

For a step-by-step guide, see the battery app with Klutter tutorial.

Written on January 2, 2022