AsyncTaskのサンプルコード(http://androidpala.com/kotlin-asynctask-android/ )をもとに、AsyncTaskを定期実行する機能を実装。アプリ起動後、AsyncTaskで2秒おきに現在時刻を取得する。トグルボタンをオフにすると現在時刻の取得が止まる。トグルボタンオンで再開する

activity_main.xml

<?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">

    <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_constraintRight_toRightOf="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" />

    <ToggleButton
        android:id="@+id/MyToggleButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginEnd="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="32dp"
        android:checked="true"
        android:text="ToggleButton"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/MyProgressBar" />

</android.support.constraint.ConstraintLayout>

MainActivity.kt

package com.example.asynctaskpractice

import android.os.AsyncTask
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.os.Handler
import android.util.Log
import android.view.View
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() {

    val Tag = "MainActivity"
    val handler = Handler()

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

        val runnable = object: Runnable {
            override fun run() {
                AsyncTaskExample().execute()
                handler.postDelayed(this, 2000)
            }
        }
        handler.post(runnable)

        MyToggleButton.setOnCheckedChangeListener { buttonView, isChecked ->
            if (isChecked) {
                Log.d(Tag, "Toggle Button is $isChecked -> Start GET Access")
                handler.post(runnable)
            } else {
                Log.d(Tag, "Toggle Button is $isChecked -> Stop GET Access")
                handler.removeCallbacks(runnable)
            }
        }
    }

    inner class AsyncTaskExample: AsyncTask<String, String, String>() {

        override fun onPreExecute() {
            super.onPreExecute()
            MyProgressBar.visibility = View.VISIBLE
        }

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

            var Result = ""
            val API_URL = "http://androidpala.com/tutorial/http.php?get=1"

            try {
                val URL = URL(API_URL)
                val connect = URL.openConnection() as HttpURLConnection

                connect.readTimeout = 8000
                connect.connectTimeout = 8000
                connect.requestMethod = "GET"
                connect.doOutput = true
                connect.connect()

                val ResponseCode = connect.responseCode
                Log.d(Tag, "ResponseCode $ResponseCode")

                if (ResponseCode == 200) {
                    val tempStream = connect.inputStream
                    if (tempStream != null) {
                        Result = ConvertToString(tempStream)
                    }
                }
            } catch (Ex: Exception) {
                Log.e("", "Error in doInBackground ${Ex.message}")
            }
            return Result
        }

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

            MyProgressBar.visibility = View.INVISIBLE
            if (result == "") {
                my_text.text = "Network Error"
            } else {
                my_text.text = result
            }
        }
    }

    fun ConvertToString(inStream: InputStream):String {
        var Result = ""
        val isReader = InputStreamReader(inStream)
        var bReader = BufferedReader(isReader)
        var temp_str: String?
        try {
            while (true) {
                temp_str = bReader.readLine()
                if (temp_str == null) { break }
                Result += temp_str
            }
        } catch (Ex: Exception) {
            Log.e(Tag, "Error in ConvertToString ${Ex.printStackTrace()}")
        }
        return Result
    }
}