Threaded Download Started Service Demo (Assignment 4)

Overview

This assignment builds upon the various Android concurrency models from the third assignment to give you experience using an Android Started Service to download bitmap images from a web server and display them via an Activity. This Activity has a similar interface as in assignment 3 and works as follows:

The Activity provides a menu of buttons and displays a default image (configured via the XML resource files). The user is prompted to enter the URL for a new bitmap image, as shown in the following screenshot:
After entering the desired URL, the user can select one of several buttons that provide different ways to download the image concurrently. The following screenshot shows how a progress dialog is displayed when downloading the designated image via the threading model:
After the URL download has completed it will be displayed in an ImageView. The following screenshot shows the displayed image:
The user can reset the image to its default contents by clicking the "Reset Image" button. The following screenshot shows the originally displayed image:

Note that the results will look somewhat different if you use a real Android smartphone vs. using the AVD emulator shown in the screenshots above.

Program Description

This assignment involves writing an Android program that has the following features:

Its AndroidManifest.xml contains (among other things) the following elements:


<uses-permission 
  android:name="android.permission.INTERNET"/>
<uses-permission 
  android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

<application
   android:icon="@drawable/ic_launcher"
   android:label="@string/app_name">
   <activity
     android:name="DownloadActivity"
     android:label="@string/app_name">
     <intent-filter>
       <action android:name="android.intent.action.MAIN"/>
       <category android:name="android.intent.category.LAUNCHER"/%gt;
     </intent-filter>
  </activity>
 
  <service android:name="ThreadedDownloadService"
      android:process=":myProcess1/>

  <service android:name="ThreadPoolDownloadService"
      android:process=":myProcess2/>

  <service android:name="DownloadIntentService"
      android:process=":myProcess3/>
</application>

It contains a DownloadActivity class that inherits from Activity and uses the XML layout containing a TextView object that prompts for the URL of the bitmap file and stores the entered URL in an EditText object.
It uses Button objects with the labels "Run IntentService Messenger", "Run ThreadPool Messenger", "Run Thread PendingIntent", "Run Async Receiver", and "Reset Image" to run the corresponding hook methods that use the URL provided by the user to start Service(s) that download the designated bitmap file via the following Android concurrency and response models:
- IntentService and Messenger model ("Run IntentService Messenger"). In this model the Service process uses an IntentService to download the designated bitmap file, stores it in the Android file system, and use a Messenger to send the filename back to the DownloadActivity process, which opens the file and displays the bitmap on the screen.
- ThreadPool and Messenger model ("Run ThreadPool Messenger"). In this model the Service process uses a ThreadPoolExecutor (e.g., via the ExecutorService configured with at least 4 threads using the newFixedThreadPool() method) to download the designated bitmap file, stores it in the Android file system, and use a Messenger to send the filename back to the DownloadActivity process, which opens the file and displays the bitmap on the screen.
- Thread and PendingIntent model ("Run Thread Pending Intent"). In this model the Service process starts a thread that downloads the designated bitmap file, stores it in the Android file system, and use a PendingIntent to send the filename back to the DownloadActivity process via it's onActivityResult() method, which opens the file and displays the bitmap on the screen.
- AsyncTask with BroadcastReceiver model ("Run Async Receiver"). In this model the Service process executes an AsyncTask that downloads the designated bitmap file, stores it in the Android file system, and use sendBroadcast() to send the filename back to a BroadcastReceiver in the DownloadActivity process, which opens the file and displays the bitmap on the screen.
See the Services handout for more discussions of these models.
The Service component(s) must run in different process(es) than the DownloadActivity component.
The Button objects that initiate the downloading of the bitmap file must be connected to the corresponding DownloadActivity.run*() methods via the appropriate android:onClick="..." attributes.
Make sure that you correctly stop your Services when you're done with them, e.g., in the DownloadActivity's onStop() or onDestroy() method.

The entire layout of the application must be structured by the contents of the Android resource files described via XML, i.e., you must not hard-code any TextView, EditText, or Button objects into your DownloadActivity class.

Skeleton Code

The following code is intended to give you some ideas of how to structure your program based on the solution I wrote. When in doubt refer to the programming assignment description above. Feel free to change this skeleton code if you have a better solution and/or submit fixes for any problems. In particular, you should refactor the code so that as many methods as possible are located in a Utils class.

Concluding Remarks

This programming assignment is more complicated than the previous one since you'll need to figure out how to pass responses back from the Service process(es) to the DownloadActivity process. There's a great deal of useful information on Android Services available on the web, but make sure not to blindly copy and paste it..

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