Hey everyone :wave::skin-tone-2: we’re trying out ...

# koin

[Cody Engel]

Hey everyone 👋🏻 we’re trying out Koin for a project and are coming from Dagger 2. I’m wondering if there is any equivalent for @Inject constructor(...) in Koin? I’d like to avoid defining every dependency in modules/components but unsure if that’s possible.

[Casey Brooks]

Yes, there is experimental support for this in koin-core-ext artifact. There are additional DSL functions which inject the primary constructor via reflection (don't need the @Inject annotation) https://insert-koin.io/docs/2.0/documentation/reference/index.html#_extensions_experimental_features

[Marko Mitic]

(I just started typing that there's no support for that 😄)

[Cody Engel]

🙇🏻 awesome thank you so much!

[Cody Engel]

@Casey Brooks actually I’m not sure if this is what I was looking for. It looks like you still have to define it in a Module?

[Marko Mitic]

I personally prefer not marking constructors as it mixes up production code with DI framework's elements. Using only modules allows for easy switching of DI frameworks/libs

[Marko Mitic]

You still have to define that class is part of DI tree but you don't have to call constructor explicitly

[Marko Mitic]

You'd still have to to that for every class used as interface with @Binds in Dagger

[Casey Brooks]

@Cody Engel Sorry, i misread the original question. Yes, I believe you will still need to register each class in a module, Koin won't automatically register classes as it constructs the graph. But it does make it significantly simpler to register classes

[Cody Engel]

Gotcha, we’re going to roll with it and see how we feel. I personally liked just defining the top level dependencies and then allowing other classes to just do their injection through the javax Inject annotation, I think it minimized the amount of ceremony.

I agree though, Koin makes it far easier to register things and get up and running.

[Casey Brooks]

You might be able to use ClassGraph to find those annotations and build those modules dynamically (https://github.com/classgraph/classgraph). It also supports build-time scanning for use on Android or for minimal runtime impact (https://github.com/classgraph/classgraph/wiki/Build-Time-Scanning)

[arnaud.giuliani]

also use koin-android-ext or koin-androidx-ext if you want automatic constructor injection for ViewModel