Completion Handler Android Kotlin

Question

I´m sorry if this question has been asked previously, I really couldn´t find anything not even simillar! I´m as well sorry if the question is dumb, I´m an iOS Developer and I´m a bit lost here in Android...

So I´m using Fuel Library(https://github.com/kittinunf/Fuel) to GET JSON data from an API... In Swift there´s something called completion handler that whenever the function finished, it will return it and immediately run the code inside it. This is an example of it in Swift:

func hardProcessingWithString(input: String, completion: (result: String) -> Void) {
    ...
    completion("we finished!")
}

What I need is to do something similar with this following function that I have in Kotlin.

fun recomendationsData() {

    Fuel.get("https://rss.itunes.apple.com/api/v1/us/apple-music/hot-tracks/10/explicit.json").response { request, response, result ->
                    println(request)
                    println(response)
                    val (bytes, error) = result
                    if (bytes != null) {
                        val str = String(bytes)
                        val obj = JSONObject(str)
                        val resultsP = obj.getJSONObject("feed")
                        val results = resultsP.getJSONArray("results")

                        for (i in 0..(results.length() - 1)) {
                            val o = results.getJSONObject(i)
                            trackName1.add(o.getString("name"))
                            trackArtist1.add(o.getString("artistName"))
                            trackImage1.add(o.getString("artworkUrl100"))
                        }


                    }
                }
}

I´ve read about something called "callback" but I really don´t understand how it works, nor how to implement it(The task must be done Asynchronously).

Thank you very much again!

Regards

Answer 1

In this case the syntax is similar to swift:

fun recommendationsData(callback: (String) -> Unit) {

Then in your function you have a function called callback that you can call with the result (change String to whatever you're returning).

Then change your function invocation from recommendationsData() to either recommendationsData(doSomething) or

recommendationsData {
    doSomethingWith(it) // or you can get named argument
    // do some more stuff
}