How To Do AsyncTask In Kotlin

 

Introduction

 

In this article, we will learn how to perform AsyncTask in Android with Kotlin. AsyncTask is used to perform some asynchronous tasks without blocking the main thread. It is very useful in Android development. Similar to Java, the same code can be used in Kotlin with some minor modifications.

 

Coding Part

 

I have divided the coding part into 3 steps as shown in the following.

• Creating a new project with Kotlin's support.
• Setting up the project with
• Implementing Async tasks with Kotlin.

Without any delay, we will start coding for Kotlin AsyncTask.

 

Step 1 - Creating a new project with Kotlin

1. Open Android Studio and select Create a new project.
2. Name the project as your wish and tick the Kotlin checkbox support.
3. Then Select your Activity type (For Example Navigation Drawer Activity, Empty Activity, etc.).
    
    
4. Then click “Finish” button to create a new project in Android Studio.

Step 2 - Setting up the project with AndroidManifest

 

Now, we will add internet permission in the Android Manifest file. Because we will see the example with the URL Connection. Just open your AndroidManifest.xml file and add the following line.

<uses-permission android:name="android.permission.INTERNET"/>

Step 3 - Implementing Async tasks with Kotlin

 

We will start coding. Here, I have used the following simple API to retrieve android version details.

 

http://demosmushtaq.16mb.com/api/post_sample.php?version_index=14

1. I have included a Button and TextView in my layout (activity_main.xml) Here, Button and TextView is used to call the API and display the result from the API

   <?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=".MainActivity"
       tools:layout_editor_absoluteX="0dp"
       tools:layout_editor_absoluteY="81dp">
   
       <TextView
           android:id="@+id/my_text"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:layout_marginEnd="8dp"
           android:layout_marginStart="8dp"
           android:layout_marginTop="72dp"
           android:text="AsyncTask Example"
           android:textSize="18sp"
           android:textStyle="bold"
           app:layout_constraintEnd_toEndOf="parent"
           app:layout_constraintStart_toStartOf="parent"
           app:layout_constraintTop_toTopOf="parent" />
   
       <ProgressBar
           android:id="@+id/MyprogressBar"
           style="?android:attr/progressBarStyle"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:layout_marginEnd="8dp"
           android:layout_marginStart="8dp"
           android:layout_marginTop="32dp"
           android:visibility="invisible"
           app:layout_constraintEnd_toEndOf="parent"
           app:layout_constraintStart_toStartOf="parent"
           app:layout_constraintTop_toBottomOf="@+id/my_text" />
   
       <Button
           android:id="@+id/CallBtn"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:layout_marginEnd="8dp"
           android:layout_marginStart="8dp"
           android:layout_marginTop="36dp"
           android:text="Execute AsyncTask"
           app:layout_constraintEnd_toEndOf="parent"
           app:layout_constraintStart_toStartOf="parent"
           app:layout_constraintTop_toBottomOf="@+id/MyprogressBar" />
   
   </android.support.constraint.ConstraintLayout>

2. Then open your Activity file (in my case kt) and create a class with AsynTask as a parent.
    
   • AsyncTask has three main methods.
      
     1. onPreExecute – State before task performance
     2. doInBackground – State for task performance
     3. onPostExecute – State after task performance

• Add the following code with your AsyncTask class.

  class AsyncTaskExample(private var activity: MainActivity?) : AsyncTask<String, String, String>() {
  
          override fun onPreExecute() {
              super.onPreExecute()
              activity?.MyprogressBar?.visibility = View.VISIBLE
          }
  
          override fun doInBackground(vararg p0: String?): String {
  
              var result = ""
              try {
                  val url = URL("http://demosmushtaq.16mb.com/api/post_sample.php?version_index=14")
                  val httpURLConnection = url.openConnection() as HttpURLConnection
  
                  httpURLConnection.readTimeout = 8000
                  httpURLConnection.connectTimeout = 8000
                  httpURLConnection.doOutput = true
                  httpURLConnection.connect()
  
                  val responseCode: Int = httpURLConnection.responseCode
                  Log.d(activity?.tag, "responseCode - " + responseCode)
  
                  if (responseCode == 200) {
                      val inStream: InputStream = httpURLConnection.inputStream
                      val isReader = InputStreamReader(inStream)
                      val bReader = BufferedReader(isReader)
                      var tempStr: String?
  
                      try {
  
                          while (true) {
                              tempStr = bReader.readLine()
                              if (tempStr == null) {
                                  break
                              }
                              result += tempStr
                          }
                      } catch (Ex: Exception) {
                          Log.e(activity?.tag, "Error in convertToString " + Ex.printStackTrace())
                      }
                  }
              } catch (ex: Exception) {
                  Log.d("", "Error in doInBackground " + ex.message)
              }
              return result
          }
  
          override fun onPostExecute(result: String?) {
              super.onPostExecute(result)
              activity?.MyprogressBar?.visibility = View.INVISIBLE
              if (result == "") {
                  activity?.my_text?.text = activity?.getString(R.string.network_error)
              } else {
                  var parsedResult = ""
                  var jsonObject: JSONObject? = JSONObject(result)
                  jsonObject = jsonObject?.getJSONObject("data")
                  parsedResult += "Code Name : " + (jsonObject?.get("code_name")) + "\n"
                  parsedResult += "Version Number : " + (jsonObject?.get("version_number")) + "\n"
                  parsedResult += "API Level : " + (jsonObject?.get("api_level"))
                  activity?.my_text?.text = parsedResult
              }
          }
      }

3. Here I have used

“HttpURLConnection” to access the API Link.

 

“BufferedReader” to read the response output of the API Link.

 

“JSONObject” to parse the response from the server.

4. Class can be called in the following method.

   AsyncTaskExample(this).execute()

Full Code of MainActivity

 

You can find the full code implementation of MainActivty.kt in the following.

class MainActivity : AppCompatActivity() {

    private val tag: String = "MainActivity"

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

        CallBtn.setOnClickListener {
            AsyncTaskExample(this).execute()
        }
    }

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

        override fun onPreExecute() {
            super.onPreExecute()
            activity?.MyprogressBar?.visibility = View.VISIBLE
        }

        override fun doInBackground(vararg p0: String?): String {

            var result = ""
            try {
                val url = URL("http://demosmushtaq.16mb.com/api/post_sample.php?version_index=14")
                val httpURLConnection = url.openConnection() as HttpURLConnection

                httpURLConnection.readTimeout = 8000
                httpURLConnection.connectTimeout = 8000
                httpURLConnection.doOutput = true
                httpURLConnection.connect()

                val responseCode: Int = httpURLConnection.responseCode
                Log.d(activity?.tag, "responseCode - " + responseCode)

                if (responseCode == 200) {
                    val inStream: InputStream = httpURLConnection.inputStream
                    val isReader = InputStreamReader(inStream)
                    val bReader = BufferedReader(isReader)
                    var tempStr: String?

                    try {

                        while (true) {
                            tempStr = bReader.readLine()
                            if (tempStr == null) {
                                break
                            }
                            result += tempStr
                        }
                    } catch (Ex: Exception) {
                        Log.e(activity?.tag, "Error in convertToString " + Ex.printStackTrace())
                    }
                }
            } catch (ex: Exception) {
                Log.d("", "Error in doInBackground " + ex.message)
            }
            return result
        }

        override fun onPostExecute(result: String?) {
            super.onPostExecute(result)
            activity?.MyprogressBar?.visibility = View.INVISIBLE
            if (result == "") {
                activity?.my_text?.text = activity?.getString(R.string.network_error)
            } else {
                var parsedResult = ""
                var jsonObject: JSONObject? = JSONObject(result)
                jsonObject = jsonObject?.getJSONObject("data")
                parsedResult += "Code Name : " + (jsonObject?.get("code_name")) + "\n"
                parsedResult += "Version Number : " + (jsonObject?.get("version_number")) + "\n"
                parsedResult += "API Level : " + (jsonObject?.get("api_level"))
                activity?.my_text?.text = parsedResult
            }
        }
    }
}

Download Code

 

You can download the sample code from the following GitHub link.