AsyncTask in Android with Kotlin

Question

How to make an API call in Android with Kotlin?

I have heard of Anko . But I want to use methods provided by Kotlin like in Android we have Asynctask for background

Answer 1

I spent a full day trying to figure how to get back the result produced by an Async Task : co-routines was my solution !!!

First, create your AsyncTask Object ... Do not forget to use corrects parameter type instead all Any

@SuppressLint("StaticFieldLeak")
class AsyncTaskExample(private var activity: MainActivity?) : AsyncTask<Any, Int, Any?>() {

    override fun onPreExecute() {
        super.onPreExecute()
        // do pre stuff such show progress bar
    }

    override fun doInBackground(vararg req: Any?): Any? {

        // here comes your code that will produce the desired result
        return result 

    }

    // it will update your progressbar
    override fun onProgressUpdate(vararg values: Int?) {
        super.onProgressUpdate(*values)

    }


    override fun onPostExecute(result: Any?) {
        super.onPostExecute(result)

        // do what needed on pos execute, like to hide progress bar
        return
    }

}

and Then, call it ( in this case, from main activity )

var task = AsyncTaskExample(this)
var req = { "some data object or whatever" }

GlobalScope.launch( context = Dispatchers.Main){

   task?.execute(req)
}

GlobalScope.launch( context = Dispatchers.Main){

   println( "Thats the result produced by doInBackgorund: " +  task?.get().toString() )
}

Answer 2

Here is an example that will also allow you to update any UI or progress displayed to the user.

Async Class

class doAsync(val handler: () -> Unit) : AsyncTask<Void, Void, Void>() {
    init {
        execute()
    }

    override fun doInBackground(vararg params: Void?): Void? {
        handler()
        return null
    }
}

Simple Usage

doAsync {
    // do work here ...

    myView.post({
        // update UI of myView ...
    })
}

Answer 3

if in the case you want to do it without using Anko and the correct way is to use the following way

open class PromotionAsyncTask : AsyncTask<JsonArray, Void, MutableList<String>>() {

private lateinit var out: FileOutputStream
private lateinit var bitmap: Bitmap
private lateinit var directory: File
private var listPromotion: MutableList<String> = mutableListOf()

override fun doInBackground(vararg params: JsonArray?): MutableList<String> {

    directory = Environment.getExternalStoragePublicDirectory("Tambo")

    if (!directory.exists()) {
        directory.mkdirs()
    }

    for (x in listFilesPromotion(params[0]!!)) {
        bitmap = BitmapFactory.decodeStream(URL(x.url).content as InputStream)
        out = FileOutputStream(File(directory, "${x.name}"))

        bitmap.compress(Bitmap.CompressFormat.PNG, 100, out)
        out.flush()
        out.close()

        listPromotion.add(File(directory, "${x.name}").toString())
    }

    return listPromotion
}

private fun listFilesPromotion(jsonArray: JsonArray): MutableList<Promotion> {
    var listString = mutableListOf<Promotion>()

    for (x in jsonArray) {
        listString.add(Promotion(x.asJsonObject.get("photo")
                .asString.replace("files/promos/", "")
                , "https://tambomas.pe/${x.asJsonObject.get("photo").asString}"))
    }

    return listString}
}

and the way to execute it is as follows

promotionAsyncTask = object : PromotionAsyncTask() {
                    override fun onPostExecute(result: MutableList<String>?) {
                        super.onPostExecute(result)
                        listFile = result!!

                        contentLayout.visibility = View.VISIBLE
                        progressLottie.visibility = View.GONE
                    }
                }
                promotionAsyncTask.execute(response!!.body()!!.asJsonObject.get("promos").asJsonArray)

Answer 4

You can get a similar syntax to Anko's fairly easy. If you just wan't the background task you can do something like

class doAsync(val handler: () -> Unit) : AsyncTask<Void, Void, Void>() {
    override fun doInBackground(vararg params: Void?): Void? {
        handler()
        return null
    }
}

And use it like

doAsync {
    yourTask()
}.execute()

Answer 5

package com.irontec.kotlintest

import android.os.AsyncTask
import android.os.Bundle
import android.support.v7.app.AppCompatActivity
import android.view.Menu
import android.view.MenuItem
import android.widget.TextView
import kotlinx.android.synthetic.main.activity_main.*
import org.json.JSONObject
import java.io.BufferedInputStream
import java.io.BufferedReader
import java.io.InputStreamReader
import java.net.HttpURLConnection
import java.net.URL


class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        GetWeatherTask(this.text).execute()
    }

    class GetWeatherTask(textView: TextView) : AsyncTask<Unit, Unit, String>() {

        val innerTextView: TextView? = textView

        override fun doInBackground(vararg params: Unit?): String? {
            val url = URL("https://raw.githubusercontent.com/irontec/android-kotlin-samples/master/common-data/bilbao.json")
            val httpClient = url.openConnection() as HttpURLConnection
            if (httpClient.responseCode == HttpURLConnection.HTTP_OK) {
                try {
                    val stream = BufferedInputStream(httpClient.inputStream)
                    val data: String = readStream(inputStream = stream)
                    return data
                } catch (e: Exception) {
                    e.printStackTrace()
                } finally {
                    httpClient.disconnect()
                }
            } else {
                println("ERROR ${httpClient.responseCode}")
            }
            return null
        }

        fun readStream(inputStream: BufferedInputStream): String {
            val bufferedReader = BufferedReader(InputStreamReader(inputStream))
            val stringBuilder = StringBuilder()
            bufferedReader.forEachLine { stringBuilder.append(it) }
            return stringBuilder.toString()
        }

        override fun onPostExecute(result: String?) {
            super.onPostExecute(result)

            innerTextView?.text = JSONObject(result).toString()

            /**
             * ... Work with the weather data
             */

        }
    }

    override fun onCreateOptionsMenu(menu: Menu): Boolean {
        menuInflater.inflate(R.menu.menu_main, menu)
        return true
    }

    override fun onOptionsItemSelected(item: MenuItem): Boolean {
        val id = item.itemId
        if (id == R.id.action_settings) {
            return true
        }
        return super.onOptionsItemSelected(item)
    }
}

link - Github Irontec

Answer 6

AsyncTask is an Android API, not a language feature that is provided by Java nor Kotlin. You can just use them like this if you want:

class someTask() : AsyncTask<Void, Void, String>() {
    override fun doInBackground(vararg params: Void?): String? {
        // ...
    }

    override fun onPreExecute() {
        super.onPreExecute()
        // ...
    }

    override fun onPostExecute(result: String?) {
        super.onPostExecute(result)
        // ...
    }
}

Anko's doAsync is not really 'provided' by Kotlin, since Anko is a library that uses language features from Kotlin to simplify long codes. Check here:

• https://github.com/Kotlin/anko/blob/d5a526512b48c5cd2e3b8f6ff14b153c2337aa22/anko/library/static/commons/src/Async.kt

If you use Anko your code will be similar to this:

doAsync {
    // ...
}