Android Background Processing
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Next episode: 04. Expect a Result From Workers
Notes: 03. Implement a Simple Worker
The student materials have been reviewed and are updated as of SEPTEMBER 2022. Image url has changed.
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After the brief revision of threading, you’re ready to start learning about more concepts in Android backround processing. The first concept you’ll cover is the WorkManager API.
implementation "androidx.work:work-runtime-ktx:2.3.4"
compileOptions {
sourceCompatibility JavaVersion.VERSION_1_8
targetCompatibility JavaVersion.VERSION_1_8
}
kotlinOptions {
jvmTarget = JavaVersion.VERSION_1_8
}
class DownloadWorker(context: Context, workerParameters: WorkerParameters) :
Worker(context, workerParameters) {
override fun doWork(): Result {
}
}
class DownloadWorker(context: Context, workerParameters: WorkerParameters) :
Worker(context, workerParameters) {
override fun doWork(): Result {
val imageUrl = URL("https://cdn.pixabay.com/photo/2018/01/14/23/12/nature-3082832__480.jpg")
val connection = imageUrl.openConnection() as HttpURLConnection
connection.doInput = true
connection.connect()
val imagePath = "owl_image.jpg"
val inputStream = connection.inputStream
val file = File(applicationContext.externalMediaDirs.first(), imagePath)
}
}
class DownloadWorker(context: Context, workerParameters: WorkerParameters) :
Worker(context, workerParameters) {
override fun doWork(): Result {
val imageUrl = URL("https://cdn.pixabay.com/photo/2018/01/14/23/12/nature-3082832__480.jpg")
val connection = imageUrl.openConnection() as HttpURLConnection
connection.doInput = true
connection.connect()
val imagePath = "owl_image.jpg"
val inputStream = connection.inputStream
val file = File(applicationContext.externalMediaDirs.first(), imagePath)
val outputStream = FileOutputStream(file)
outputStream.use { output ->
val buffer = ByteArray(4 * 1024)
var byteCount = inputStream.read(buffer)
while (byteCount > 0) {
output.write(buffer, 0, byteCount)
byteCount = inputStream.read(buffer)
}
output.flush()
}
return Result.success()
}
}
private fun downloadImage() {
val constraints = Constraints.Builder()
.setRequiresBatteryNotLow(true)
.setRequiresStorageNotLow(true)
.setRequiredNetworkType(NetworkType.NOT_ROAMING)
.build()
}
private fun downloadImage() {
val constraints = Constraints.Builder()
.setRequiresBatteryNotLow(true)
.setRequiresStorageNotLow(true)
.setRequiredNetworkType(NetworkType.NOT_ROAMING)
.build()
val downloadRequest = OneTimeWorkRequestBuilder<DownloadWorker>()
.setConstraints(constraints)
.build()
}
private fun downloadImage() {
val constraints = Constraints.Builder()
.setRequiresBatteryNotLow(true)
.setRequiresStorageNotLow(true)
.setRequiredNetworkType(NetworkType.NOT_ROAMING)
.build()
val downloadRequest = OneTimeWorkRequestBuilder<DownloadWorker>()
.setConstraints(constraints)
.build()
val workManager = WorkManager.getInstance(this)
workManager.enqueue(downloadRequest)
}
private fun downloadImage() {
val constraints = Constraints.Builder()
.setRequiresBatteryNotLow(true)
.setRequiresStorageNotLow(true)
.setRequiredNetworkType(NetworkType.NOT_ROAMING)
.build()
val downloadRequest = OneTimeWorkRequestBuilder<DownloadWorker>()
.setConstraints(constraints)
.build()
val workManager = WorkManager.getInstance(this)
workManager.enqueue(downloadRequest)
workManager.getWorkInfoByIdLiveData(downloadRequest.id).observe(this, Observer { info ->
if (info.state.isFinished) {
val imageFile = File(externalMediaDirs.first(), "owl_image.jpg")
displayImage(imageFile.absolutePath)
}
})
}
private fun displayImage(imagePath: String) {
GlobalScope.launch(Dispatchers.Main) {
val bitmap = loadImageFromFile(imagePath)
image.setImageBitmap(bitmap)
}
}
private suspend fun loadImageFromFile(imagePath: String): Bitmap =
withContext(Dispatchers.IO) { BitmapFactory.decodeFile(imagePath) }