Coming from C++/Qt/QML land, just got started on Kotlin/Compose about 2 weeks ago. So far so good, I believe this is a really nice and powerful library. Most difficult part to understand for me is how do you expose some of your business logic to the UI? Say I have a service for making grpc calls. How do i access the services from my Composable functions? Do I need to create some sort of Service Locator? Use Dependency injection? What is the right pattern to use for exposing backend services or adapters to the frontend?

Hi! There are many ways to do this. The two most simple solutions: • either instantiate your services in the main function, and pass them down through the composable calls as parameters • or you can use

remember

to instantiate your services directly in the composables

Right. But I just need my services to be instantiated once, not mutlitplied by the number of functions.

I’d explore using an architecture pattern like MVVM coupled with a dependency injection framework like Koin or Dagger - these allow for handling the instantiation of single/multiple instances of services 👍

I don't to pass the services down to all my functions... That would be terrible!

Because Compose was created by Android devs, and the ecosystem is not yet completely in place for non-Android environments 😕

My advice is using a state management and/or navigation library.

A lot of this will be simpler with context receivers, but that's not for the near future

Don't pass services down to all your functions. Instead, structure your App in pages or screens or sections. Each of the above will represent and operate on a corresponding State class(sealed class most of the time). Said state is usually called ViewModel, it will be served to your first function or the root function in your screen. Then each part/section of your screen will map to a section in that big encapsulating State, that precisely does that, encapsulates smaller states. All the grpc, network, whatever logic and state mutation happens in that ViewModel or parent State. You then update the section of the State and the compose machinery will call the corresponding composable function that renders the recently updated state, the way you wanted to render it

> Why do you always need to use extra libraries for such simple things as a Service Locator? Because they make it easy? I'm not sure what your expectation is here. In any other scenario, you'd still be using some sort of a library to handle your deps for you. In Java land, Guice is an example, as is Spring. Handrolling your own DI/locator is too much boilerplate and it's never worth it.

Nice. Like the idea of the ViewModel indeed, which I already tried. But wanted some expert feedback first 🙂

There’s plenty of toolings within androidx.compose for testing: https://developer.android.com/jetpack/compose/testing

All of this is Android-only, no?

Ahh for Kotlin Mutliplatform compose you can use *`org.jetbrains.compose.uk:ui-test-junit4`* instead

ok thanks a lot!