Download Content Provider Demo (Assignment 6)

Overview

This assignment gives you experience with several variants of an Android ContentProvider to download bitmap images from a web server and display them via an Activity that communicates to the ContentProvider via a ContentResolver. This Activity has a similar user interface as previous assignments 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.
After entering the desired URL, the user can select one of several buttons that provide different ways to download the image.
After the URL download has completed it will be displayed in an ImageView.
The user can reset the image to its default contents by clicking the "Reset Image" button.

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>
 
  <provider android:name=".DownloadContentProvider"
      android:process=":my_process/>

  <service android:name=".DownloadService"
      android:process=":my_process/>
</application>

It contains a DownloadActivity class that extends 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 five Button objects with the labels "Download File", "Query via query()", "Query via CursorLoader", "Query via AsyncQueryHandler", and "Reset Image" to run the corresponding hook methods that use the URL provided by the user to download and display the designated bitmap file as follows:
- Download File. Activity uses the Async AIDL model from assignment 5 to request a Bound Service download the bitmap at the designated URL and store it in the application's internal storage. The Service should then create a URI for the file that indicates file metadata (e.g., the timestamp for when the file was downloaded represented as a long) and insert the corresponding URI for the file into an SQLite database in the ContentProvider (defined in your AndroidManifest.xml file) along with metadata about the file. The callback AIDL method returns the URI to the Activity, which displays the URI as a Toast to indicate the bitmap was downloaded successfully (but don't display the actual bitmap at this point).
- Query via query(). The DownloadActivity spawns a Thread (or an AsyncTask) that calls query() on the ContentResolver to request that the associated ContentProvider to provide a Cursor containing the file that matches the URI back to thread, which opens the file and causes the bitmap to be displayed on the screen.
- Query via CursorLoader. The DownloadActivity uses a CursorLoader to return a Cursor containing the file that matches the URI back to thread, which opens the file and causes the bitmap to be displayed on the screen back to DownloadActivity as an onLoadFinished() callback, which opens the file and causes the bitmap to be displayed on the screen.
- Query via AsyncQueryHandler. The DownloadActivity uses an AsyncQueryHandler to return a Cursor containing the file that matches the URI back to thread, back to DownloadActivity as an onQueryComplete() callback, which opens the file and causes the bitmap to be displayed on the screen.
See the Services handout for more discussions of these models.
The ContentProvider 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.

Concluding Remarks

This programming assignment builds upon the previous assignments. I'm not providing any skeleton code, so feel free to design your solution as you see fit. We may also change the program specification as we learn more about how these Android features work.

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

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