Thursday, February 13, 2020

android kotlin - Coroutines flow api example

MainActivity.kt 

package com.example.jetpack

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import kotlinx.android.synthetic.main.activity_main.*
import kotlinx.coroutines.*
import kotlinx.coroutines.flow.Flow
import kotlinx.coroutines.flow.collect
import kotlinx.coroutines.flow.flow
import kotlinx.coroutines.flow.flowOn


class MainActivity : AppCompatActivity() {

    lateinit var flow:Flow<String>
    lateinit var colors:List<String>

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

        setupFlow()
        setupClicks()

        colors = listOf(
            "African violet",
            "Air superiority blue",
            "Alloy orange",
            "Antique bronze",
            "Arylide yellow",
            "Atomic tangerine",
            "Bittersweet shimmer"
        )
    }


    @ExperimentalCoroutinesApi
    private fun setupFlow(){
        flow = flow{
           colors.forEach {
               delay(1000)
               emit(it)
           }
        }.flowOn(Dispatchers.Default)
    }


    private fun setupClicks(){
        button.setOnClickListener {
            textView.text = ""
            CoroutineScope(Dispatchers.Main).launch {
                flow.collect{
                    textView.append("\n"+it)
                }
            }
        }
    }
}
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">
    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="16dp"
        android:text="Show Color List"
        android:backgroundTint="#E30022"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:text=""
        android:textAppearance="@style/TextAppearance.AppCompat.Large"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button" />
</androidx.constraintlayout.widget.ConstraintLayout>
build.gradle dependencies [add] 

// Kotlin coroutines
implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:1.3.3"
implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:1.3.3"
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