@@ -144,3 +144,98 @@ private class DownloadTask extends AsyncTask<String, Integer, String> {
144144```
145145
146146### 从服务器上下载文件
147+ 148+ 这里有个最大的问题:* 我怎么从service来更新我的activity?* 。
149+ 在下一个例子当中我们会使用两个你可能不熟悉的类:`ResultReceiver `和`IntentService `。`ResultReceiver `是一个可以允许我们用Service 来更新线程的类;`IntentService `是一个可以生成用来处理后台任务的线程的`Service `子类(你需要知道,`Service `实际上是和你的应用运行在同一个线程的;当你继承了`Service `之后,你必须手动生成一个新的线程来处理费时操作)。
150+ 151+ 一个提供下载功能的`Service `看起来像这样:
152+ 153+ ```java
154+ public class DownloadService extends IntentService {
155+ public static final int UPDATE_PROGRESS = 8344 ;
156+ public DownloadService () {
157+ super (" DownloadService"
158+ }
159+ @Override
160+ protected void onHandleIntent (Intent intent ) {
161+ String urlToDownload = intent. getStringExtra(" url"
162+ ResultReceiver receiver = (ResultReceiver ) intent. getParcelableExtra(" receiver"
163+ try {
164+ URL url = new URL (urlToDownload);
165+ URLConnection connection = url. openConnection();
166+ connection. connect();
167+ // 这对你在进度条上面显示百分比很有用
168+ int fileLength = connection. getContentLength();
169+ 170+ // download the file
171+ InputStream input = new BufferedInputStream (connection. getInputStream());
172+ OutputStream output = new FileOutputStream (" /sdcard/BarcodeScanner-debug.apk"
173+ 174+ byte data[] = new byte [1024 ];
175+ long total = 0 ;
176+ int count;
177+ while ((count = input. read(data)) != - 1 ) {
178+ total += count;
179+ // 更新进度条....
180+ Bundle resultData = new Bundle ();
181+ resultData. putInt(" progress" int ) (total * 100 / fileLength));
182+ receiver. send(UPDATE_PROGRESS , resultData);
183+ output. write(data, 0 , count);
184+ }
185+ 186+ output. flush();
187+ output. close();
188+ input. close();
189+ } catch (IOException e) {
190+ e. printStackTrace();
191+ }
192+ 193+ Bundle resultData = new Bundle ();
194+ resultData. putInt(" progress" 100 );
195+ receiver. send(UPDATE_PROGRESS , resultData);
196+ }
197+ }
198+ ```
199+ 200+ 把这个`Service `添加到清单文件中:
201+ ```
202+ < service android: name= " .DownloadService" / >
203+ ```
204+ 205+ activity里面的代码:
206+ 207+ ```java
208+ // 像第一个例子里面一样初始化ProgressBar
209+ 210+ // 在这里启动下载
211+ mProgressDialog.show ();
212+ Intent intent = new Intent (this , DownloadService . class);
213+ intent.putExtra ("url ", "url of the file to download ");
214+ intent.putExtra ("receiver ", new DownloadReceiver (new Handler ()));
215+ startService (intent );
216+ ```
217+ 218+ 然后像这样来使用`ResultReceiver `:
219+ 220+ ```java
221+ private class DownloadReceiver extends ResultReceiver {
222+ public DownloadReceiver (Handler handler ) {
223+ super (handler);
224+ }
225+ 226+ @Override
227+ protected void onReceiveResult (int resultCode , Bundle resultData ) {
228+ super . onReceiveResult(resultCode, resultData);
229+ if (resultCode == DownloadService . UPDATE_PROGRESS
230+ int progress = resultData. getInt(" progress"
231+ mProgressDialog. setProgress(progress);
232+ if (progress == 100 ) {
233+ mProgressDialog. dismiss();
234+ }
235+ }
236+ }
237+ }
238+ ```
239+ 240+ #### 使用Groundy 库
241+ [Groundy](http:// casidiablo.github.com/groundy)
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