I came across an odd thing (and didn’t find anything on :google: ) I have a delegate property. Insid...

# android

[pablisco]

I came across an odd thing (and didn’t find anything on google )
I have a delegate property. Inside this property I call a method that requires API 23. I’ve marked the property with: @get:RequiresApi(23) however, I’m still getting a lint about the use of a new API level.
I’ll add more details as a thread…

[pablisco]

This is the delegate:

fun <V: View, T> shared(
    block: V.() -> T
): ReadOnlyProperty<V, T> =
    object : ReadOnlyProperty<V, T> {

        override fun getValue(thisRef: V, property: KProperty<*>): T =
            restoreOrCreate(thisRef, block)
                .also { thisRef.setTag(R.id.view_cache, it) }

        @Suppress("UNCHECKED_CAST")
        private fun restoreOrCreate(thisRef: V, block: V.() -> T) =
            thisRef.getTag(R.id.view_cache) as? T ?: thisRef.block()
    }

It’s a bit like by lazy but relies on the view’s tag

[pablisco]

Then the code where I’m getting the error is written like this:

@get:RequiresApi(VERSION_CODES.M)
val <V : View> V.plusDrawable: Flow<Pair<ScrollBy, ScrollBy>> by shared {
    callbackFlow {
        setOnScrollChangeListener { _, x, y, oX, oY ->
            offer((x to y) to (oX to oY))
        }
    }
}

[pablisco]

image.png

[pablisco]

I’m very puzzled since it has the annotation 🤔

[pablisco]

If I remove the getter modifier I get this error, which is understandable tbh

[Giorgos Neokleous]

🤔 interesting, I am going to wildly guess that it has to do with callbackFlow unwrapping. Does the lint persist if you move the setOnScrollChangeListener outside of the callback flow?

[pablisco]

Yeah, same problem. I’m thinking that something in the delegate shared is confusing Lint 🤔

[pablisco]

And even adding @get:SuppressLint(“NewApi”) has zero effect 😭

[pablisco]

I ended adding this:

@SuppressLint("NewApi")
private fun View.setOnScrollChangeListenerUnsafe(listener: OnScrollChangeListener?) =
    setOnScrollChangeListener(listener)

Not sure if it’s a problem with Lint or Kotlin 🤔

[Ryan Mentley]

delegates and annotations get very weird sometimes

[Ryan Mentley]

the short version is that they don't necessarily end up applied to the spot you'd expect

[Ryan Mentley]

not quite the same thing, but in the vein of this: https://youtrack.jetbrains.com/issue/KT-32770