Your first coroutine with Kotlin

pljp/kotlinx.coroutines

build.gradle (Modlue.app)

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    ・・・
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.1.1'
    implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:1.3.2" // step1
 
}

package com.nekotype.ips.api
 
import android.os.AsyncTask
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.util.Log
import kotlinx.android.synthetic.main.activity_main.*
import kotlinx.coroutines.*　// step2
 
 
class MainActivity : AppCompatActivity() {
 
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
 
         // click
        button.setOnClickListener {
           println("start: ${Thread.currentThread().name}")
            GlobalScope.launch{
                println("coroutine: ${Thread.currentThread().name}")
            }
            println("end: ${Thread.currentThread().name}")
        }
 
    }
}
 
 ↓
start: main
end: main
coroutine: DefaultDispatcher-worker-1

// thread version
import kotlinx.coroutines.*
import java.util.concurrent.atomic.AtomicLong
import kotlin.concurrent.thread
 
fun main() {
    val c = AtomicLong()
 
    for (i in 1..1_000_000L)
// thread だと数秒まっても終了しないので諦めた
        thread(start = true) {
            c.addAndGet(i)
        }
 
    println(c.get())
 
}
 
　↓
// coroutines version
import kotlinx.coroutines.*
import java.util.concurrent.atomic.AtomicLong
import kotlin.concurrent.thread
 
fun main() {
    runBlocking {
        val sum = deferred.sumBy { it.await() }
        println("Sum: $sum")
    }
}
 
val deferred = (1..1_000_000).map { n ->
    GlobalScope.async {
        n
    }
}
 
// Sum: 1784293664

import kotlinx.coroutines.*
import java.util.concurrent.atomic.AtomicLong
import kotlin.concurrent.thread
 
fun main() {
    runBlocking {
        val sum = deferred.sumBy { it.await() }
        println("Sum: $sum")
    }
}
 
val deferred = (1..1_000_000).map { n ->
    GlobalScope.async {
        delay(1000)
 
        n
    }
}
 ↓
Sum: 1784293664

launchやasyncで新しいcoroutineを作成するが、Dispatchers.Mainで簡単にmainスレッドを呼び出せる。
今までのdoInBackgroundでpublishProgressを使ってonProgressUpdateを呼び出すようなことをしなくてよくなる。

package com.nekotype.ips.myapplication
 
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.util.Log
import kotlinx.android.synthetic.main.activity_main.*
import kotlinx.coroutines.*
import java.text.SimpleDateFormat
import java.util.*
 
class MainActivity : AppCompatActivity() {
 
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
 
        val format = SimpleDateFormat("kk:mm:ss")
 
        Log.d("async", "${text1.text} ${format.format(Date())} : ouerLaunch1 : ${Thread.currentThread().name}\n\n")
 
        GlobalScope.launch {
 
            Log.d("async", "${text1.text} ${format.format(Date())} : inLaunch1 : ${Thread.currentThread().name}\n\n")
 
            async{
                delay(3000)
                Log.d("async", "${text1.text} ${format.format(Date())} : async1 : ${Thread.currentThread().name}\n\n")
            }
 
            Log.d("async", "${text1.text} ${format.format(Date())} : inLaunch2 : ${Thread.currentThread().name}\n\n")
 
 
            async(Dispatchers.Main) {
                delay(1000)
                Log.d("async", "${text1.text} ${format.format(Date())} : async2 : ${Thread.currentThread().name}\n\n")
            }
 
            async {
                delay(500)
                Log.d("async","${text1.text} ${format.format(Date())} : async3 : ${Thread.currentThread().name}\n\n")
                async(Dispatchers.Main) {
                    Log.d("async", "${text1.text} ${format.format(Date())} : inAsync3 : ${Thread.currentThread().name}\n\n")
                }
 
            }
 
        }
 
        Log.d("async","${text1.text} ${format.format(Date())} : ouerLaunch2 : ${Thread.currentThread().name}\n\n")
    }
}
 
　↓
 
05:32:14 : ouerLaunch1 : main
05:32:14 : ouerLaunch2 : main
05:32:14 : inLaunch1 : DefaultDispatcher-worker-1
05:32:14 : inLaunch2 : DefaultDispatcher-worker-1
05:32:14 : async3 : DefaultDispatcher-worker-1
05:32:14 : inAsync3 : main // ⇒ worker-1 の内側からmainを呼び出している
05:32:15 : async2 : main
05:32:17 : async1 : DefaultDispatcher-worker-3

        Log.d(  "coroutine","start")
        GlobalScope.launch(Dispatchers.Main) {
                Log.d(  "coroutine","coroutin")
                Text.text="click" // 画面のテキストを変更する
        }
        Log.d(  "coroutine","end")
   ↓
2020-01-14 06:24:17.847 7602-7602/com.nekotype.ips.coroutine D/coroutine: start
2020-01-14 06:24:17.847 7602-7602/com.nekotype.ips.coroutine D/coroutine: end
2020-01-14 06:24:17.849 7602-7602/com.nekotype.ips.coroutine D/coroutine: coroutin

    private var myjob:Job? =null
    private  var myjobs= mutableListOf<Job?>()

    ...
        myjob=GlobalScope.launch {
            progress_countdown.max=1000
    ...
    
    // 画面を閉じた場合にコルーチンをキャンセル
    override fun onPause() {
        super.onPause()
        myjobs.map {
            Log.d("choice","cancel")
            it?.cancel()
        }
    }

コルーチン内で他のコルーチンの終了を待機する。

    fun TestCoroutin(){
        Log.d(  "coroutine","start")
        GlobalScope.launch() {
 
            launch {
                Log.d(  "coroutine","coroutin_inner")
            }
 
            Log.d(  "coroutine","coroutin_outer")
        }
        Log.d(  "coroutine","end")
    }
    ↓
2020-01-14 06:29:12.311 7952-7952/com.nekotype.ips.coroutine D/coroutine: start
2020-01-14 06:29:12.340 7952-7952/com.nekotype.ips.coroutine D/coroutine: end
2020-01-14 06:29:12.347 7952-7998/com.nekotype.ips.coroutine D/coroutine: coroutin_outer
2020-01-14 06:29:12.348 7952-7999/com.nekotype.ips.coroutine D/coroutine: coroutin_inner

　↓

    fun TestCoroutin(){
        Log.d(  "coroutine","start")
        GlobalScope.launch() {
 
            launch {
                Log.d(  "coroutine","coroutin_inner")
            }.join() // 待つ
 
            Log.d(  "coroutine","coroutin_outer")
        }
        Log.d(  "coroutine","end")
    }
    ↓
2020-01-14 06:30:51.472 8058-8058/com.nekotype.ips.coroutine D/coroutine: start
2020-01-14 06:30:51.500 8058-8058/com.nekotype.ips.coroutine D/coroutine: end
2020-01-14 06:30:51.505 8058-8111/com.nekotype.ips.coroutine D/coroutine: coroutin_inner　//順番が変わる
2020-01-14 06:30:51.508 8058-8110/com.nekotype.ips.coroutine D/coroutine: coroutin_outer　//順番が変わる

runBlockingとasyncは戻り値をもつことができる。
asyncは非同期に処理する。asyncにはawaitでまつことができる。