Android AsyncTask: You can interact with the UI thread (Main Thread) with AsynTask when you have to do some background task. AsyncTask class performs background operations and publishes results on the UI thread without having to manipulate threads.
In your application, you can use the android AsyncTask class for short operations or tasks ( few seconds), for the long-running operation you have to choose another option.
AysnTask performs an operation (or any task) in the background and publishes results in UI Thread. An asynchronous task is defined by 3 generic types, called,ParamsProgress and Result.
Params, the parameters sent to the task upon execution.Progress, the progress units published during the background computation.Result, the result of the background computation.
if you don’t want to pass any value then pass parameters Void.
private class MyTask extends AsyncTask<Void, Void, Void> {... }There are 4 methods in Async task: onPreExecute, doInBackground, onProgressUpdate and onPostExecute.
onPreExecute(), invoked on the UI thread before the task is executed.doInBackground(Params...), invoked on the background thread immediately afteronPreExecute()finishes executing.onProgressUpdate(Progress...), invoked on the UI thread after a call topublishProgress(Progress...).onPostExecute(Result), invoked on the UI thread after the background computation finishes.
How to cancel AsyncTask
A task can be canceled at any time by invoking cancel(boolean) method. Invoking this method will cause subsequent calls to isCancelled() to return true. So you can check Task has canceled or not.
Rules of Using AsyncTask
- The first rule AsyncTask class must be loaded on the UI thread, it will be done automatically.
execute(Params...)must be invoked on the UI thread.- Do not call
onPreExecute(),onPostExecute(Result),doInBackground(Params...),onProgressUpdate(Progress...)manually. - The task can be executed only once (an exception will be thrown if a second execution is attempted.)
How to Use – Let’s Build AsyncTask android example
This example we are downloading data from GitHub API in string format and showing in TextView.
Step 1. Create new project “Build Your First Android App in Kotlin“
Step 2. add internet permissions in manifest.xml, for internet connection
<manifest>
<uses-permission android:name="android.permission.INTERNET"/>
....
</manifest>Step 3. Add flowing code in resource file main_activity.xml
TextView -> will show result
ProgressBar will visible when downloading start and invisible after the task has completed
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="in.eyehunt.androidasynctaskkotlin.MainActivity">
<TextView
android:id="@+id/tv_result"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:text="Data will show !"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.029"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<ProgressBar
android:id="@+id/progressBar"
style="?android:attr/progressBarStyleHorizontal"
android:layout_width="213dp"
android:layout_height="26dp"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="220dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.503"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
android:visibility="gone"
android:indeterminate="true"/>
</android.support.constraint.ConstraintLayout>
Step 4. Create an inner class in MainActivity kotlin class and extend AsyncTask class
package `in`.eyehunt.androidasynctaskkotlin
import android.app.AlertDialog
import android.app.Dialog
import android.app.ProgressDialog
import android.opengl.Visibility
import android.os.AsyncTask
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.util.Log
import android.view.View
import android.widget.ProgressBar
import kotlinx.android.synthetic.main.activity_main.*
import java.io.BufferedReader
import java.io.InputStream
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)
val url = URL("https://api.github.com/search/users?q=eyehunt")
MyAsyncTask().execute(url)
}
// AsyncTask inner class
inner class MyAsyncTask : AsyncTask<URL, Int, String>() {
private var result: String = "";
override fun onPreExecute() {
super.onPreExecute()
progressBar.visibility = View.VISIBLE
}
override fun doInBackground(vararg params: URL?): String {
val connect = params[0]?.openConnection() as HttpURLConnection
connect.readTimeout = 8000
connect.connectTimeout = 8000
connect.requestMethod = "GET"
connect.connect();
val responseCode: Int = connect.responseCode;
if (responseCode == 200) {
result = streamToString(connect.inputStream)
}
return result
}
override fun onProgressUpdate(vararg values: Int?) {
super.onProgressUpdate(*values)
}
override fun onPostExecute(result: String?) {
super.onPostExecute(result)
progressBar.visibility = View.GONE
//set result in textView
tv_result.text = result
}
}
fun streamToString(inputStream: InputStream): String {
val bufferReader = BufferedReader(InputStreamReader(inputStream))
var line: String
var result = ""
try {
do {
line = bufferReader.readLine()
if (line != null) {
result += line
}
} while (line != null)
inputStream.close()
} catch (ex: Exception) {
}
return result
}
}
Step 4. Run the application, in the emulator or on your android device
Output screenshot Android AsyncTask example in kotlin
Download Android AsyncTask example source code :
https://github.com/EyeHunts/AndroidAsyncTaskKotlin/
Note : This example (Project) is developed in Android Studio 3.0.1 ,tested on Android 7.1.1 ( Android Nougat), compile SDK version API 26: Android 8.0 (Oreo)
MinSdkVersion=”15″
TargetSdkVersion=”26″
Coding in Kotlin