Hi all, I’ve worked on a project where we used a B...

# android

[Michael Pohl]

Hi all, I’ve worked on a project where we used a BaseFragment that looked like this:

abstract class ViewModelFragment<VM : BaseViewModel>(@LayoutRes val layout: Int, private val viewModelClass: KClass<VM>) :
    BaseFragment() {

    open lateinit var viewModel: VM

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        viewModel = getViewModel(viewModelClass)
        return inflater.inflate(layout, container, false)
    }
}

The idea was to remove as much boilerplate noise in the fragment classes as possible. This project also used Koin for DI, this class uses Koin's getViewModel() to set the viewModel.

What I don’t like about this approach is that subclasses of this have a constructor that looks like this:

class AudioPlayerFragment : ViewModelFragment<AudioPlayerViewModel>(R.layout.fragment_audio_player, AudioPlayerViewModel::class)

As you can see, for this to work, you need a type annotation and still have to hand in the KClass type, which is just ugly.

So I’m wondering if there is any way to get this to just look like this:

class MyFragment<MyViewModel> : ViewModelFragment(myLayout) {}

I understand that there is a limitation as to what Kotlin can do with generics and that I’m basically looking for what `reified`functions can do, but on a class, and that that’s no new question. I was hoping to find a solution like this here: https://stackoverflow.com/a/48398303/8746644

But I can’t figure out a way that would work with Fragments and sub classes . I could also see writing a custom getViewModel function to deal with the type, but I don’t know how. Does anybody have a suggestion how I could achieve what I want in a reasonable way?

[wasyl]

I believe you’d need https://youtrack.jetbrains.com/issue/KT-33213 for that

[Michael Pohl]

Yes that would make sense, but as far as I see this doesn’t exist yet in any proper way to use it in a production grade Android app.
I was hoping there is some kind of different approach that would allow me to inject my viewModel and maintain compatibility with the Android APIs while having a simple constructor structure like I wrote above, maybe through some helper structure or so.
Anyway, I don’t see how to do it properly with what I have at hand currently, it’s possible that the status quo is: this doesn’t work.