Thursday, July 16, 2020

android kotlin - Coroutines async

MainActivity.kt

package com.example.coroutine

import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import kotlinx.android.synthetic.main.activity_main.*
import kotlinx.coroutines.*
import java.io.BufferedReader
import java.io.InputStreamReader
import java.net.URL


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

        // url to get html
        val url:URL = URL("https://developer.android.com/")

        button.setOnClickListener {
            // creates a coroutine and returns its future result
            // as an implementation of deferred

            // async task to get html as string from url
            val result: Deferred<String> = GlobalScope.async {
                url.getHtml()
            }


            // global scope is used to launch top-level coroutines which are
            // operating on the whole application lifetime
            GlobalScope.launch(Dispatchers.Main) {
                // show html as string when available
                textView.text = result.await()
            }
        }
    }
}


// extension function to get html from url
fun URL.getHtml():String {
    val reader = BufferedReader(InputStreamReader(this.openStream()))
    var input: String? = ""
    val stringBuffer = StringBuffer()
    while (reader.readLine().also { input = it } != null) {
        stringBuffer.append(input)
    }
    reader.close()
    return stringBuffer.toString ()
}
activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.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"
    android:background="#EDEAE0">

    <com.google.android.material.button.MaterialButton
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:text="Get HTML"
        android:backgroundTint="#665D1E"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <com.google.android.material.textview.MaterialTextView
        android:id="@+id/textView"
        style="@style/TextAppearance.MaterialComponents.Headline6"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:padding="8dp"
        android:layout_marginTop="16dp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button"
        tools:text="Hello World!" />

</androidx.constraintlayout.widget.ConstraintLayout>
build.gradle (app) [dependencies]

// kotlin coroutine
implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-core:1.3.7'
implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.3.7'