| There are many ways to download files. Following I will post most common ways; it is up to you to decide which method is better for your app. 1. Use AsyncTask and show the download progress in a dialog This method will allow you to execute some background processes and update the UI at the same time (in this case, we'll update a progress bar). This is an example code: // declare the dialog as a member field of your activityProgressDialog mProgressDialog;// instantiate it within the onCreate methodmProgressDialog = new ProgressDialog(YourActivity.this);mProgressDialog.setMessage("A message");mProgressDialog.setIndeterminate(true);mProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);mProgressDialog.setCancelable(true);// execute this when the downloader must be firedfinal DownloadTask downloadTask = new DownloadTask(YourActivity.this);downloadTask.execute("the url to the file you want to download");mProgressDialog.setOnCancelListener(new DialogInterface.OnCancelListener() { @Override public void onCancel(DialogInterface dialog) { downloadTask.cancel(true); }});
The AsyncTask will look like this: // usually, subclasses of AsyncTask are declared inside the activity class.// that way, you can easily modify the UI thread from hereprivate class DownloadTask extends AsyncTask<String, Integer, String> { private Context context; private PowerManager.WakeLock mWakeLock; public DownloadTask(Context context) { this.context = context; } @Override protected String doInBackground(String... sUrl) { InputStream input = null; OutputStream output = null; HttpURLConnection connection = null; try { URL url = new URL(sUrl[0]); connection = (HttpURLConnection) url.openConnection(); connection.connect(); // expect HTTP 200 OK, so we don't mistakenly save error report // instead of the file if (connection.getResponseCode() != HttpURLConnection.HTTP_OK) { return "Server returned HTTP " + connection.getResponseCode() + " " + connection.getResponseMessage(); } // this will be useful to display download percentage // might be -1: server did not report the length int fileLength = connection.getContentLength(); // download the file input = connection.getInputStream(); output = new FileOutputStream("/sdcard/file_name.extension"); byte data[] = new byte[4096]; long total = 0; int count; while ((count = input.read(data)) != -1) { // allow canceling with back button if (isCancelled()) { input.close(); return null; } total += count; // publishing the progress.... if (fileLength > 0) // only if total length is known publishProgress((int) (total * 100 / fileLength)); output.write(data, 0, count); } } catch (Exception e) { return e.toString(); } finally { try { if (output != null) output.close(); if (input != null) input.close(); } catch (IOException ignored) { } if (connection != null) connection.disconnect(); } return null; }
The method above (doInBackground) runs always on a background thread. You shouldn't do any UI tasks there. On the other hand, the onProgressUpdate and onPreExecute run on the UI thread, so there you can change the progress bar: @Override protected void onPreExecute() { super.onPreExecute(); // take CPU lock to prevent CPU from going off if the user // presses the power button during download PowerManager pm = (PowerManager) context.getSystemService(Context.POWER_SERVICE); mWakeLock = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, getClass().getName()); mWakeLock.acquire(); mProgressDialog.show(); } @Override protected void onProgressUpdate(Integer... progress) { super.onProgressUpdate(progress); // if we get here, length is known, now set indeterminate to false mProgressDialog.setIndeterminate(false); mProgressDialog.setMax(100); mProgressDialog.setProgress(progress[0]); } @Override protected void onPostExecute(String result) { mWakeLock.release(); mProgressDialog.dismiss(); if (result != null) Toast.makeText(context,"Download error: "+result, Toast.LENGTH_LONG).show(); else Toast.makeText(context,"File downloaded", Toast.LENGTH_SHORT).show(); }
For this to run, you need the WAKE_LOCK permission. <uses-permission android:name="android.permission.WAKE_LOCK" />
2. Download from Service The big question here is: how do I update my activity from a service?. In the next example we are going to use two classes you may not be aware of: ResultReceiver and IntentService. ResultReceiver is the one that will allow us to update our thread from a service; IntentService is a subclass of Service which spawns a thread to do background work from there (you should know that a Service runs actually in the same thread of your app; when you extends Service, you must manually spawn new threads to run CPU blocking operations). Download service can look like this: public class DownloadService extends IntentService { public static final int UPDATE_PROGRESS = 8344; public DownloadService() { super("DownloadService"); } @Override protected void onHandleIntent(Intent intent) { String urlToDownload = intent.getStringExtra("url"); ResultReceiver receiver = (ResultReceiver) intent.getParcelableExtra("receiver"); try { URL url = new URL(urlToDownload); URLConnection connection = url.openConnection(); connection.connect(); // this will be useful so that you can show a typical 0-100% progress bar int fileLength = connection.getContentLength(); // download the file InputStream input = new BufferedInputStream(connection.getInputStream()); OutputStream output = new FileOutputStream("/sdcard/BarcodeScanner-debug.apk"); byte data[] = new byte[1024]; long total = 0; int count; while ((count = input.read(data)) != -1) { total += count; // publishing the progress.... Bundle resultData = new Bundle(); resultData.putInt("progress" ,(int) (total * 100 / fileLength)); receiver.send(UPDATE_PROGRESS, resultData); output.write(data, 0, count); } output.flush(); output.close(); input.close(); } catch (IOException e) { e.printStackTrace(); } Bundle resultData = new Bundle(); resultData.putInt("progress" ,100); receiver.send(UPDATE_PROGRESS, resultData); }}
Add the service to your manifest: <service android:name=".DownloadService"/>
And the activity will look like this: // initialize the progress dialog like in the first example// this is how you fire the downloadermProgressDialog.show();Intent intent = new Intent(this, DownloadService.class);intent.putExtra("url", "url of the file to download");intent.putExtra("receiver", new DownloadReceiver(new Handler()));startService(intent);
Here is were ResultReceiver comes to play: private class DownloadReceiver extends ResultReceiver{ public DownloadReceiver(Handler handler) { super(handler); } @Override protected void onReceiveResult(int resultCode, Bundle resultData) { super.onReceiveResult(resultCode, resultData); if (resultCode == DownloadService.UPDATE_PROGRESS) { int progress = resultData.getInt("progress"); mProgressDialog.setProgress(progress); if (progress == 100) { mProgressDialog.dismiss(); } } }}
2.1 Use Groundy library Groundy is a library that basically helps you run pieces of code in a background service, and it is based on the ResultReceiver concept shown above. This library is deprecated at the moment. This is how the whole code would look like: The activity where you are showing the dialog... public class MainActivity extends Activity { private ProgressDialog mProgressDialog; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); findViewById(R.id.btn_download).setOnClickListener(new View.OnClickListener() { public void onClick(View view) { String url = ((EditText) findViewById(R.id.edit_url)).getText().toString().trim(); Bundle extras = new Bundler().add(DownloadTask.PARAM_URL, url).build(); Groundy.create(DownloadExample.this, DownloadTask.class) .receiver(mReceiver) .params(extras) .queue(); mProgressDialog = new ProgressDialog(MainActivity.this); mProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL); mProgressDialog.setCancelable(false); mProgressDialog.show(); } }); } private ResultReceiver mReceiver = new ResultReceiver(new Handler()) { @Override protected void onReceiveResult(int resultCode, Bundle resultData) { super.onReceiveResult(resultCode, resultData); switch (resultCode) { case Groundy.STATUS_PROGRESS: mProgressDialog.setProgress(resultData.getInt(Groundy.KEY_PROGRESS)); break; case Groundy.STATUS_FINISHED: Toast.makeText(DownloadExample.this, R.string.file_downloaded, Toast.LENGTH_LONG); mProgressDialog.dismiss(); break; case Groundy.STATUS_ERROR: Toast.makeText(DownloadExample.this, resultData.getString(Groundy.KEY_ERROR), Toast.LENGTH_LONG).show(); mProgressDialog.dismiss(); break; } } };}
A GroundyTask implementation used by Groundy to download the file and show the progress: public class DownloadTask extends GroundyTask { public static final String PARAM_URL = "com.groundy.sample.param.url"; @Override protected boolean doInBackground() { try { String url = getParameters().getString(PARAM_URL); File dest = new File(getContext().getFilesDir(), new File(url).getName()); DownloadUtils.downloadFile(getContext(), url, dest, DownloadUtils.getDownloadListenerForTask(this)); return true; } catch (Exception pokemon) { return false; } }}
And just add this to the manifest: <service android:name="com.codeslap.groundy.GroundyService"/>
It couldn't be easier I think. Just grab the latest jar from Github and you are ready to go. Keep in mind that Groundy's main purpose is to make calls to external REST apis in a background service and post results to the UI with easily. If you are doing something like that in your app, it could be really useful. 2.2 Use https://github.com/koush/ion 3. Use DownloadManager class (GingerBread and newer only) GingerBread brought a new feature, DownloadManager, which allows you to download files easily and delegate the hard work of handling threads, streams, etc. to the system. First, let's see a utility method: /** * @param context used to check the device version and DownloadManager information * @return true if the download manager is available */public static boolean isDownloadManagerAvailable(Context context) { if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.GINGERBREAD) { return true; } return false;}
Method's name explains it all. Once you are sure DownloadManager is available, you can do something like this: String url = "url you want to download";DownloadManager.Request request = new DownloadManager.Request(Uri.parse(url));request.setDescription("Some descrition");request.setTitle("Some title");// in order for this if to run, you must use the android 3.2 to compile your appif (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) { request.allowScanningByMediaScanner(); request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);}request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, "name-of-the-file.ext");// get download service and enqueue fileDownloadManager manager = (DownloadManager) getSystemService(Context.DOWNLOAD_SERVICE);manager.enqueue(request);
Download progress will be showing in the notification bar. | 