Convert javascript code to Kotlin - Android

Support
1

I have an algorithm in javascript that works as a “prioritizer”, where I have an array with items to be priorized, and then, a javascript prompt appears for user choose one of the pair of items that appears and then, the algorithm makes the prioritization. It is here: http://jsfiddle.net/alexandre9865/bq3ey1pc/2/

I’m trying to adapt it to kotlin with an user interface, but I have one problem: the function promptInput called inside the second while in insertionSort function.
The function promptInput in javascript is asynchronous, has any approach in kotlin about that?

override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
): View? {
    val root = inflater.inflate(R.layout.fragment_main, container, false)
    pair1 = root!!.findViewById(R.id.pair1) as Button
    pair2 = root!!.findViewById(R.id.pair2) as Button

    pair1!!.setOnClickListener {
        insertionSort(pair1!!.text.toString())
    }
    pair2!!.setOnClickListener {
        insertionSort(pair2!!.text.toString())
    }

fun main() {
    val arr = arrayOf("homework", "chores", "shopping")
    val result = insertionSort("What needs to be done first", arr)
    println(result.toList())
}

fun promptInput(comparison: String, str1: String, str2: String): String {
    println("$comparison: $str1 or $str2?");// i want to set the buttons pair1 and pair2 with texts of str1 and str2, and when the user click in one of them, the function returns to the while where it was called
    return readLine()!!
}

fun insertionSort(comparison: String, arr: Array<String>): Array<String> {
    println("arr size: ${arr.size}")
    var len = arr.size
    var i = -1
    var j: Int
    var tmp: String

    while (len-- != 0) {
        tmp = arr[++i];
        j = i
        while (j-- != 0 && (promptInput(comparison, arr[j], tmp) == arr[j])) {
            arr[j + 1] = arr[j];
        }
        arr[j + 1] = tmp
    }

    return arr.apply { reverse() }
}
2

Have you tried prompt like in your JS code? It’s available in Kotlin as well.

EDIT: Ah, it looks like from your onCreateView you’re talking about Android. I thought you were talking about Kotlin/JS instead.

1 Like
3

exactly, it is android in my case

4

make both insertionSort and promptInput suspend functions. Then in your onClickListener, wrap the call to insertionSort with lifecycleScope.launch { insertionSort(...) }
Then in insertionSort, wrap all of the function body with withContext(Dispatchers.Default), and in promptInput wrap the body with withContext(Dispatchers.Main)

All of this is basically making sure that all the asynchronous work is done on an appropriate thread/threadpool. Threads might be a bit foreign for a js developer, but think of them kind of like web workers.

6

How can I implement the withContext if the insertionSort has a parameter? @kyay10

    suspend fun insertionSort withContext(Dispatchers.Default) (choice: String): Array<String>  {
    println("arr size: ${arr.size}")
    var len = arr.size
    var i = -1
    var j: Int
    var tmp: String

    while (len-- != 0) {
        tmp = arr[++i];
        j = i
        while (j-- != 0 && (promptInput(comparison, arr[j], tmp) == arr[j])) {
            arr[j + 1] = arr[j];
        }
        arr[j + 1] = tmp
    }

    return arr.apply { reverse() }
}
7

I think it would be helpful to follow the Kotlin Koans if you haven’t already. There’s also a special hands-on for coroutines.

I did the Koans a long time ago so they may have changed (they look like they’ve been updated quite a bit). There are other learning resources available here.

It seems some of your questions are good beginner material-- Instead of waiting for someone to reply to each one, it might be a lot faster and more convenient for you to work through using those tutorials :slight_smile:

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