AsyncTask in Android with Kotlin

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 operations.

Solution 1:

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 {
    // ...
}

Solution 2:

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()

Solution 3:

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 ...
    })
}

Solution 4:

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

Solution 5:

AsyncTask was deprecated in API level 30. To implement similar behavior we can use Kotlin concurrency utilities (coroutines).

Create extension function on CoroutineScope:

fun <R> CoroutineScope.executeAsyncTask(
        onPreExecute: () -> Unit,
        doInBackground: () -> R,
        onPostExecute: (R) -> Unit
) = launch {
    onPreExecute()
    val result = withContext(Dispatchers.IO) { // runs in background thread without blocking the Main Thread
        doInBackground()
    }
    onPostExecute(result)
}

Now it can be used on any CoroutineScope instance, for example, in ViewModel:

class MyViewModel : ViewModel() {

      fun someFun() {
          viewModelScope.executeAsyncTask(onPreExecute = {
              // ...
          }, doInBackground = {
              // ...
              "Result" // send data to "onPostExecute"
          }, onPostExecute = {
              // ... here "it" is a data returned from "doInBackground"
          })
      }
  }

or in Activity/Fragment:

lifecycleScope.executeAsyncTask(onPreExecute = {
      // ...
  }, doInBackground = {
      // ...
      "Result" // send data to "onPostExecute"
  }, onPostExecute = {
      // ... here "it" is a data returned from "doInBackground"
  })

To use viewModelScope or lifecycleScope add next line(s) to dependencies of the app's build.gradle file:

implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:$LIFECYCLE_VERSION" // for viewModelScope
implementation "androidx.lifecycle:lifecycle-runtime-ktx:$LIFECYCLE_VERSION" // for lifecycleScope