Android Background Processing

To finish off the WorkManager and DownloadManager practice, you first have to solve a challenge! In this challenge, you have to replace the SynchronizeImageWorker code, with the DownloadManager. Here’s a hint, you can extract the code for the DownloadManager, to the FileUtils, and then reuse it for each image you have to download!

That’s it, now pause the video, and solve the challenge, then once you’re done, unpause the video, and compare the two solutions! :] Good luck!

Let’s start off by creating two functions to help out with queueing work. Open the FileUtils class, and add the following code:

  fun queueImagesForDownload(context: Context, images: Array<String>) {
    if (images.isNotEmpty()) {
      val downloadManager = context.getSystemService(DownloadManager::class.java)

      val requests = images.mapNotNull { imageUrl ->
        val file = File(context.externalMediaDirs.first(), imageUrl)

        buildDownloadManagerRequest(file, imageUrl)
      }

      requests.forEach { request -> downloadManager?.enqueue(request) }
    }
  }
  

This function will prepare the DownloadManager and iterate over the files, preparing the requests for the manager.

To finish this off, create the buildDownloadManagerRequest() function, like so:

private fun buildDownloadManagerRequest(file: File, imageUrl: String): DownloadManager.Request? {
    return DownloadManager.Request(Uri.parse("$BASE_URL/files/$imageUrl"))
        .setTitle("Image download")
        .setDescription("Downloading")
        .setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE)
        .setDestinationUri(Uri.fromFile(file))
        .setAllowedOverMetered(true)
        .setAllowedOverRoaming(false)
  }

It is very simple, as you’ve just extrapolated the code from the previous examples you’ve had to download images.

Now head over to the SynchronizeImagesWorker, and replace the download code with the next function call:

FileUtils.queueImagesForDownload(applicationContext, images)

This will cover the synchronization part of the app. Head over to the ImagesFragment, and replace the DownloadManager call, with the following:

FileUtils.queueImagesForDownload(requireContext(), arrayOf(imageUrl))

Way to go! :] Now run the app, and check that everything works correctly!