In essence, JetBrains has caught up to where Xamarin was prior to the announcement of Xamarin.Forms: the ability from one solution to have separate iOS and Android UI applications with a business logic library shared between the two, all written in C# or F# (the two languages supported by the Mono compiler). The main difference is that one of the vendors actually supports the language in question (Kotlin) as a first-class citizen.
And going the other way, there's been noise for a couple years that Android apps could be written in Swift, achieving the same effect in reverse.
Windows isn't a mobile platform. They tried 2.5 times and have given up. In mobile it's iOS and Android, and neither Apple nor Google recognize C# as a first-class language. If you can write a compiler that emits code that LLVM can compile to ARM binary with Xcode or package your MSIL with a micro .NET VM on Android, then more power to you but Apple and Google aren't going to help you if you get stuck.
The thing that I still don't know about are how would things like data persistence be handled in a cross platform manner?
I recently built a kotlin Android app for work, and our architecture is tightly coupled to Android's Room database and LiveData objects. Obviously if we build it to be cross platform we wouldn't be able to use a Room database or LiveData objects on an iOS device. Would we have to roll our own persistence layer in a cross platform application? Or would we share business logic but still write a persistence layer using platform specific code?
It's not just persistence too. Any lower level API provided by the platform would still need to be written twice, right? Accessing the camera, the devices GPS location, or anything hardware related still needs an implementation for both platforms. Or would we eventually see libraries that would abstract this layer out, similar to react native?
Edit: Another thought...I haven't done much iOS development but the whole async nature of Android apps with the UI thread and background threads also seems like it would be a nightmare to deal with in a cross platform way. Does iOS involve a lot of async threads?
I think the way is to write libraries for these use-cases. There is already a persistence lib for Kotlin Native called KNArch.db https://github.com/touchlab/knarch.db and it supports Android too.
We are already using libraries to make easier to use background threads (RxJava, RxSwift) so I don't think it's that hard to implement a cross platform lib for that purpose. JetBrains is already trying to tackle the task with Coroutines for Kotlin Native: https://github.com/Kotlin/kotlinx.coroutines/tree/master/nat...
Looks great! My biggest concern and one of the reasons I'm not using Swift or C++ for a cross platform library is that most of the dependencies you (at least I need) need don't support those languages (Auth0, Firebase, Crashlytics etc...). So you end up writing more complex code to make that also work. If Kotlin native can bring those types of libraries to be supported it will be huge IMO.
In a nutshell this has the same limitation has Xamarin.
The Business Logic is shared , but the UI Logic and the Technical Logic aren't shared or not completely.
The Xamarin community has been struggling with this issue for half a decade and they ended up re-writting their own rendering engine (similar to Flutter) in C# on top of Xamarin to obtain truly MVVM Cross-Platform Framework.
My point here is very simple , getting Kotlin to run on iOS is great, but it's somewhat a waste of time because of how much time and effort it would talk to create a Runtime or Rendering Engine to normalize UI/UX on differents platforms.
It's similar, but not the same. The details matter. They're different because you don't need to deal with a complex abstraction layer to share logic. As in, you can expose an iOS Framework and call it from swift/Objc just like any other library. That lets you share tested logic and architecture, and do so optionally. It's not all-or-nothing. Xamarin is a different approach. Flutter is a very different approach.
Part of the issue when evaluating frameworks is expectations and not understand the plusses/minuses. If you are looking for a framework that will do 1 codebase for all logic and UI, without sacrificing any UX or capabilities, you'll probably be let down. Kotlin Multiplatform will be great for sharing logic and architecture. UI is somewhat of a different case. Why Xamarin wasn't great here is you need to do EVERYTHING in Xamarin, and write custom bridge code when not. It's an entirely different world, which bad IDE support for most of it's history. Jetbrains makes excellent tools, and if you understand that the UI will be "native", then there's a lot of efficiencies you can leverage here. If you get frustrated because you can't make one thing do all things, then yeah, it'll let you down.
The difference is that Kotlin has first class support on Android. Aside from that I agree, Kotlin is obviously second class on iOS. IMHO for simple multi-platform projects I'd use either plain webtechs or react-native. The impedance mismatch between Kotlin and Swift/ObjC is going to be an hindrance no matter what.
I wouldn't call manually exporting Java methods to the WebWidget "no effort whatsover", plus the performance hit of doing cross-language, inter-process calls, in a dynamic language while the platform languages are static.
> I wouldn't call manually exporting Java methods to the WebWidget "no effort whatsover", plus the performance hit of doing cross-language, inter-process calls, in a dynamic language while the platform languages are static.
Well like it or not JS is first class on both platforms as they both have a JS engine at the developer's disposal, Kotlin or C# aren't.
That's not what first class means to you. You can't just make up the definition you want just because it's convenient for your. First class means it runs on the platform without any form of external or third party runtime.
So, so excited for this. I would love nothing more than to be able to create Model and ViewModel code a domain specific cross platform SDK, and have a View implementation on a platform by platform basis for android, iOS, and web. Possible? I sure hope so!