Thursday, July 16, 2020

android kotlin - Coroutines start undispatched

MainActivity.kt

package com.example.coroutine

import android.graphics.Color
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import kotlinx.android.synthetic.main.activity_main.*
import kotlinx.coroutines.*


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

        button.setOnClickListener {
            // set text color by checkbox checked state
            if (checkBox.isChecked){
                textView.setTextColor(Color.parseColor("#800020"))
                textView.text = "1. CoroutineStart.UNDISPATCHED"
            }
            else{
                textView.setTextColor(Color.parseColor("#8DB600"))
                textView.text = "1. CoroutineStart.DEFAULT"
            }


            GlobalScope.launch(
                Dispatchers.Main ,
                if (checkBox.isChecked){
                    // immediately executes coroutine until its first
                    // suspension point in the current thread
                    CoroutineStart.UNDISPATCHED
                }else{
                    // immediately schedules coroutine for execution
                    // according to its context
                    CoroutineStart.DEFAULT
                }
            ) {
                textView.append("\n\n2. Inside coroutine, before delay.")
                delay(5000)
                textView.append("\n\n3. Delayed 5 seconds.")
            }

            textView.append("\n\n4. Outside coroutine, after coroutine.")
        }
    }
}
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.textview.MaterialTextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="16dp"
        tools:text="Hello World!"
        style="@style/TextAppearance.MaterialComponents.Headline6"
        app:layout_constraintHorizontal_bias="0.534"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button" />

    <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="Click Me"
        android:backgroundTint="#4B5320"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <CheckBox
        android:id="@+id/checkBox"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="32dp"
        android:text="UNDISPATCHED"
        app:layout_constraintBottom_toBottomOf="@+id/button"
        app:layout_constraintStart_toEndOf="@+id/button"
        app:layout_constraintTop_toTopOf="@+id/button" />

</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'