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Implement an AsyncTask

The student materials have been reviewed and are updated as of SEPTEMBER 2022.

Implement an AsyncTask, the notorious wholesome API for background processing and returning values from the background.

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Even though the AlarmManager is the first API that came in Android, for scheduling work in some way, you’ll cover the AsyncTask first.

class DownloadImageTask(private val onImageLoaded: (Bitmap) -> Unit) : AsyncTask<String, String, Bitmap>() {

}
class DownloadImageTask(private val onImageLoaded: (Bitmap) -> Unit) : AsyncTask<String, String, Bitmap>() {

  override fun doInBackground(vararg params: String?): Bitmap {
    val imagePath = params[0] ?: throw IllegalArgumentException("No url provided!")
    val imageUrl = URL(imagePath)
    val connection = imageUrl.openConnection() as HttpURLConnection
  }
}
class DownloadImageTask(private val onImageLoaded: (Bitmap) -> Unit) : AsyncTask<String, String, Bitmap>() {

  override fun doInBackground(vararg params: String?): Bitmap {
    val imagePath = params[0] ?: throw IllegalArgumentException("No url provided!")
    val imageUrl = URL(imagePath)
    val connection = imageUrl.openConnection() as HttpURLConnection

    connection.doInput = true
    connection.connect()

    val inputStream = connection.inputStream
    try {
      return BitmapFactory.decodeStream(inputStream)
    } catch (error: Throwable) {
      error.printStackTrace()
    }

    throw IllegalArgumentException("No image")
  }
}
...
  override fun onPostExecute(result: Bitmap?) {
    super.onPostExecute(result)

    if (result != null) {
      onImageLoaded(result)
    }
  }
...
val imagePath = "https://cdn.pixabay.com/photo/2017/11/30/11/57/barn-owl-2988291_960_720.jpg"
val task = DownloadImageTask { bitmap ->
  image.setImageBitmap(bitmap)
}

task.execute(imagePath)

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