Kotlin annotation - Require a parameter is a Constant variable from specific class

Question

I have a function filter here

fun filter(category: String) {
...
}

and a Class with many constant string

object Constants {
    val CAT_SPORT = "CAT_SPORT"
    val CAT_CAR = "CAT_CAR"
    ...
}

How to ensure the parameter category is a constant string from Constants (or throw warning)?

I am looking for something like @StringRes.

I know Enum may do the trick but prefer not to code refactor at this moment.

perhaps you can program that on your own, it's easy with annotation processor — apksherlock
– apksherlock, Commented Jul 30, 2019 at 8:43

gpunto · Accepted Answer · 2019-07-30 08:44:30Z

7

Using androidx.annotation you can do something like this:

object Constants {
    @Retention(AnnotationRetention.SOURCE)
    @StringDef(CAT_SPORT, CAT_CAR)
    annotation class Category

    const val CAT_SPORT = "CAT_SPORT"
    const val CAT_CAR = "CAT_CAR"
}

fun filter(@Constants.Category category: String) {
    ...
}

answered Jul 30, 2019 at 8:44

gpunto

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