Epoxy: EpoxyAttribute generate problem for Kotlin

[minibugdev]

I try to apply EpoxyAttribute to field in Kotlin, like below:

@EpoxyModelClass(layout = R.layout.model_epoxy)
abstract class TestEpoxyModel(@EpoxyAttribute @ColorInt var color: Int) : EpoxyModel<View>() {
    override fun bind(view: View?) {
        view?.setBackgroundColor(color)
    }
}

And got error on compile annotation, like below:

com.airbnb.epoxy.EpoxyProcessorException: EpoxyAttribute annotations must not be on private or static fields. (class: TestEpoxyModel, field: color)
e: Some error(s) occurred while processing annotations. Please see the error messages above.

[geralt-encore]

The problem is that in Kotlin backing fields of properties are private which are not allowed by epoxys annotation processor.

@elihart I've solved the same issue in StorIO.
The solution was to allow annotate not only actual fields but methods as well - getters in our case.
It looks like that:

@StorIOSQLiteType(table = "tweets") data class Tweet @StorIOSQLiteCreator constructor(@get:StorIOSQLiteColumn(name = "author") val author: String,
                                                  @get:StorIOSQLiteColumn(name = "content") val content: String)

I am not sure that it is the best solution, but it was at least the easiest one to integrate into current codebase. As a bonus it also allows to use annotation on AutoValue classes since they can be used on methods.

[minibugdev]

@geralt-encore Thank you for solution but its doesn't work both @get:EpoxyAttribute and @field:EpoxyAttribute.

For my solution, I added @JvmField @EpoxyAttribute to the field and it work properly.

[geralt-encore]

@minibugdev sorry, I wasn't clear enough. It wasn't a solution for you case - it was a proposal to @elihart how it could be possibly solved in a more kotlin way.
@JvmField works as a temporary workaround tho.

[elihart]

@geralt-encore Thanks for chiming in. I don't have much experience with Kotlin unfortunately so I'm glad you know what's going on.

I'm glad it can be solved with JvmField. Very interesting idea to allow annotating getter methods with EpoxyAttribute. I'm not ready to spend the time going down that path myself right now, but would be open to a PR if somebody really wants it.

[geralt-encore]

I can look into it later. I haven't even started with lint check yet, so can't promise anything.

[elihart]

@geralt-encore Thanks! The linting thing isn't a priority, especially since the processor supports configuration options to fail for usage errors now. I think linting would be cool, but it would probably also be a lot of work, so no rush on that :P

Let me know if you think of any other things that could change to better support kotlin. I'm excited by the 1.1 release - I'm just waiting for kotlin support in Buck (which we use to build) before I start using it more.

[geralt-encore]

Kotlin is awesome! I don't really like these @JvmField or annotating getter solutions - they don't feel natural and looks ugly. The only thing that we need to do to be able to annotate Kotlin properties directly is to overcome annotation private fields restriction. I might have an idea how to solve it. Will try to investigate it tomorrow.

[geralt-encore]

@elihart so looks like you are in the middle of huge changes for 2.0 version. Should I wait for it before introducing new stuff to annotation processor?

[elihart]

@geralt-encore yep! although https://github.com/airbnb/epoxy/pull/140 should be the last major change. If you want to work against the 2.0 branch after the PR is merged that could work, I'm not planning any more major conflicts to the processor or generated tests so you probably wouldn't have issues with merge conflicts.

I'd prefer not to take any PR's against master if they touch a lot of processor code or tests since the merge conflicts could be bad against 2.0.

[Leeeyou]

@geralt-encore thank you so much .

    @Inject
    private Observable<RiBao> storyObservable;

Remove the private solution to my problem

[zaihuishou]

@majapw @geralt-encore @elihart I hava same problem,this is my code @EpoxyModelClass(layout = R.layout.item_category) abstract class CategoryModel(@JvmField @EpoxyAttribute var name: String = "") :EpoxyModel<TextView({ override fun bind(view: TextView?) { view?.text = name } }
it can not generate CategoryModel_ class

[elihart]

@zaihuishou You don't need @JvmField

@EpoxyModelClass(layout = R.layout.item_category)
abstract class CategoryModel(@EpoxyAttribute var name: String = "") :EpoxyModel<TextView> { 
      override fun bind(view: TextView?) { view?.text = name }
}

what is the error exactly?

[zaihuishou]

@elihart i solved it. change annotationProcessor 'com.airbnb.android:epoxy-processor:2.2.0' to
kapt 'com.airbnb.android:epoxy-processor:2.2.0'

[elihart]

@zaihuishou oh good! I just made this change to hopefully help other people with that https://github.com/airbnb/epoxy/commit/60dbfd406c538e1d0700d841031081e9d67ff565

[JayyyR]

Was there a solution this without having to add @JvmField? I'm still seeing that as an issue when I want to use @ModelProp to expose something to the Epoxy Model

[elihart]

@JayyyR sounds like you're talking about usage inside a view with @ModelView, which is a separate issue. The one in this issue was solved.

For @ModelView components JvmField is still required - you could open a new issue to track supporting that

[JayyyR]

@elihart ah I see, thanks for pointing that out. Do you know if there's a way to use @ModelProp purely as a way to expose a getter? It doesn't seem to be designed for that and an IllegelArgumentException is thrown if I expose a ModelProp and the setter isn't called.

Basically I need access to a property on the view inside the Epoxy model

[elihart]

No, a model prop is intended mainly as a setter - data should flow from the model to the view, not the other way around.

I'm not sure the use case you have to get a property off the view, but you could try setting a callback via the model

[JayyyR]

yea I see your point. I guess what I really need is access to my generic ViewModel class from the EpoxyModel. I thought I could get an instance of the ViewModel through the View.

Basically trying to do something in the ViewModel when onBind is called

[JayyyR]

Oh hang on I see we have a reference to the view in the OnModelBoundListener. i think I can achieve what I need that way