Threaded Download Bound Service Demo (Assignment 5)

Overview

This assignment builds upon the various Android concurrency models from the third assignment and fourth assignment to give you experience with two variants of an Android Bound Service to download bitmap images from a web server and display them via an Activity that communicates to the Bound Services via AIDL. This Activity has a similar user interface as assignment 4 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="DownloadBoundServiceSync"
      android:process=":my_process/>

  <service android:name="DownloadBoundServiceASync"
      android:process=":my_process/>
  </activity>

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 three Button objects with the labels "Run Sync AIDL", "Run Async AIDL", and "Reset Image" to run the corresponding hook methods that use the URL provided by the user to start the appropriate Bound Service that downloads the designated bitmap file via the following two Android concurrency and AIDL models:
- Sync AIDL model ("Run Sync AIDL"). In this model the DownloadActivity spawns a Thread (or an AsyncTask), binds to a DownloadBoundServiceSync process, and uses a synchronous twoway AIDL method invocation to request that this service (1) download a designated bitmap file, (2) store it in the Android file system, and (3) use the return value from the synchronous AIDL method invocation to return the filename back to thread, which opens the file and causes the bitmap to be displayed on the screen. You'll need a single *.aidl file with a single AIDL interface for this model.
- Async AIDL model ("Run Async AIDL"). In this model the DownloadActivity binds to a DownloadBoundServiceAsync process and uses an asynchronous oneway AIDL method invocation to request that this service (1) download a designated bitmap file, (2) store it in the Android file system, and use another oneway AIDL interface passed as a parameter to the original oneway AIDL method invocation to return the filename back to DownloadActivity as a callback, which opens the file and causes the bitmap to be displayed on the screen. You'll need a two *.aidl files with two AIDL interfaces (one for the callback interface and one for the callback registration interface) for this model.
See the Services handout for more discussions of these models.
The DownloadBoundServiceSync and DownloadBoundServiceAsync components must run in different processes 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.

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.

Implementation Considerations

The following are implementation considerations for assignment 5:

AIDL Files -- The following are the AIDL files you'll need for this assignment.

Sync AIDL AIDL model. This model requires just one AIDL interface in a single file:
```
interface DownloadCall 
{
    String downloadImage (in Uri uri);
}
```

Async AIDL AIDL model. This model requires two AIDL interfaces in two AIDL different files:


interface DownloadCallback {
    oneway void sendPath (in String imageFilePath); 
}

interface DownloadRequest {
    oneway void downloadImage (in Uri uri, in DownloadCallback callback); 
}

Concluding Remarks

This programming assignment builds upon the previous two assignments, but should actually be somewhat less code to write since AIDL and the Android Binder will do more of the work for you (once you figure out how they work). I'm not providing any skeleton code this time, so feel free to design your solution as you see fit.

There's a great deal of useful information on Android AIDL and Binder available on the web and in your textbook, but make sure not to blindly copy and paste it..

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