android kotlin - Coroutines with timeout or null







MainActivity.kt



package com.example.coroutine

import android.graphics.Bitmap
import android.graphics.BitmapFactory
import android.os.Bundle
import android.view.View
import androidx.appcompat.app.AppCompatActivity
import androidx.lifecycle.*
import kotlinx.android.synthetic.main.activity_main.*
import kotlinx.coroutines.*
import java.io.IOException
import java.net.MalformedURLException
import java.net.URL


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

// url of image to download
val urlImage:URL? = try {
URL("https://images.pexels.com/photos/298246/" +
"pexels-photo-298246.jpeg?" +
"auto=compress&cs=tinysrgb&dpr=2&h=750&w=1260")
}catch (e:MalformedURLException){
button.isEnabled = false
button2.isEnabled = false
textView.text = e.message
null
}


button.setOnClickListener {
urlImage?.apply {
asyncImageDownload(this, 600)
}
}


button2.setOnClickListener {
urlImage?.apply {
asyncImageDownload(this, 12000)
}
}
}


// asynchronously download image from url with predefined timeout value
private fun asyncImageDownload(url:URL,timeout:Long){
textView.text = "Image downloading. Timeout $timeout milliseconds.\n"
progressBar.visibility = View.VISIBLE

val result : Deferred<Bitmap?> = lifecycleScope.async(Dispatchers.IO) {
url.toBitmap()
}

lifecycleScope.launch(Dispatchers.Main){
// coroutine with a specified timeout and
// returns null if this timeout was exceeded
val bitmap : Bitmap? = withTimeoutOrNull(timeout){
result.await()
}

if (bitmap == null){
textView.append("\nTimed out. Download failed.")
imageView.setImageBitmap(null)
progressBar.visibility = View.INVISIBLE
}else{
textView.append("\nDownload finish.")
imageView.setImageBitmap(bitmap)
progressBar.visibility = View.INVISIBLE
}
}
}
}


// extension function to get / download bitmap from url
fun URL.toBitmap(): Bitmap?{
return try {
BitmapFactory.decodeStream(openStream())
}catch (e: IOException){
null
}
}





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"
android:background="#ECEBBD"
tools:context=".MainActivity">

<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:backgroundTint="#FF2400"
android:text="Download 600 ms"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />

<com.google.android.material.button.MaterialButton
android:id="@+id/button2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:backgroundTint="#FF2400"
android:text="12000 ms"
app:layout_constraintBottom_toBottomOf="@+id/button"
app:layout_constraintStart_toEndOf="@+id/button"
app:layout_constraintTop_toTopOf="parent" />

<ProgressBar
android:id="@+id/progressBar"
style="?android:attr/progressBarStyle"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:visibility="invisible"
app:layout_constraintBottom_toBottomOf="@+id/button2"
app:layout_constraintStart_toEndOf="@+id/button2"
app:layout_constraintTop_toTopOf="@+id/button2" />

<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:layout_marginTop="12dp"
android:padding="8dp"
android:fontFamily="sans-serif-thin"
android:textColor="#59260B"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/button"
tools:text="TextView" />

<ImageView
android:id="@+id/imageView"
android:layout_width="0dp"
android:layout_height="300dp"
android:layout_marginTop="8dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/textView"
tools:srcCompat="@tools:sample/avatars" />

</androidx.constraintlayout.widget.ConstraintLayout>





build.gradle (app) [code to add]



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

// life cycle
def lifecycle_version = "2.2.0"
implementation "androidx.lifecycle:lifecycle-livedata-ktx:$lifecycle_version"
implementation "androidx.lifecycle:lifecycle-extensions:$lifecycle_version"
implementation "androidx.lifecycle:lifecycle-runtime-ktx:$lifecycle_version"
}










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