Threaded Download Demo (Assignment 3)

Overview

The purpose of this assignment is to give you experience using various Android concurrency models to download bitmap images from a web server. The application 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 the AVD emulator vs. using a real Android smartphone shown in the screenshots above.

Program Description

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

Its AndroidManifest.xml contains the following:


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

It contains a ThreadedDownloadActivity 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 four Button objects with the label "Run Runnable", "Run Messages", "Run Async", and "Reset Image" to run the corresponding hook methods that use the URL provided by the user to download the designated bitmap file via one of the following three Android concurrency models:
- Handlers and Runnables model ("Run Runnables"), which was described in the Handlers and Runnables portion of the Android Concurrency and Synchronization lecture.
- Handlers and Messages model ("Run Messages"), which was described in the Handlers and Messages portion of the Android Concurrency and Synchronization lecture.
- AsyncTask model ("Run Async"), which was described in the AsyncTask portion of the Android Concurrency and Synchronization lecture.
Should any of these downloads fail you should produce a warning indicator via a Toast and/or EditText field. As this is most likely called from the background thread performing the download the toast or field update must forced to the UI Thread via one of the means we discussed in class.
The Button objects that download the bitmap file must be connected to the corresponding ThreadedDownloadActivity.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 ThreadedDownloadActivity 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. Feel free to change this skeleton code if you have a better solution.


package examples.threadeddownloads;

import android.app.Activity;
import android.os.AsyncTask;
import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;

import android.app.ProgressDialog;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.EditText;
import android.widget.ImageView;

import android.widget.ProgressBar;
import android.util.Log;
import java.io.IOException;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.StatusLine;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpUriRequest;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.util.EntityUtils;

public class ThreadedDownloadActivity extends Activity {
    // ... you fill in here

    @Override
    public void onCreate(Bundle savedInstanceState) {
        // ... you fill in here
    }

    Bitmap downloadBitmap (String url) {
        // ... you fill in here
    }

    public void runRunnable(View view) {
        // ... you fill in here
    }

    public void runMessages(View view) {
        // ... you fill in here
    }

    public void runAsyncTask(View view) {
        // ... you fill in here
    }

    public void resetImage(View view) {
        // ... you fill in here
    }
}

Concluding Remarks

This programming assignment is more complicated than the first one. There's a great deal of useful information on Android concurrency models and HTTP client programming available on the web.

Back to CS 282 home page.