Android中使用IntentService執行背景工作

Android中使用IntentService執行背景工作

IntentService提供了一種在後台線程中執行任務的方式，適合處理執行時間較長的背景工作。

優點：

（1）IntentService運行在單獨的線程中，不會阻塞UI線程

（2）IntentService不受生命週期的影響

缺點：

（1）不能與UI直接進行互動，可以用Broadcast

（2）順序執行請求，第二個請求只有在第一個請求執行完以後才能執行

（3）請求不能被中斷

 

使用IntentService的步驟：

（1）在Activity中通過startService啟動service，並傳遞參數。

（2）Service中接收參數，做耗時的處理，處理完畢，發送Broadcat，並把處理結果傳遞出來

（3）Activity中註冊BroadcastReceiver，監聽廣播，更新UI。

 

看一個例子：

 

public class MainActivity extends Activity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);Button btn = (Button) this.findViewById(R.id.btn);btn.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {//通過startService啟動service，並傳遞參數。Intent mServiceIntent = new Intent(MainActivity.this,RSSPullService.class);mServiceIntent.setData(Uri.parse(http://www.baidu.com/));MainActivity.this.startService(mServiceIntent);}});//註冊BroadcastReceiver，監聽廣播IntentFilter statusIntentFilter = new IntentFilter(Constants.BROADCAST_ACTION);        // Sets the filter's category to DEFAULT        statusIntentFilter.addCategory(Intent.CATEGORY_DEFAULT);DownloadStateReceiver mDownloadStateReceiver = new DownloadStateReceiver();// Registers the DownloadStateReceiver and its intent filtersLocalBroadcastManager.getInstance(this).registerReceiver(mDownloadStateReceiver, statusIntentFilter);}private class DownloadStateReceiver extends BroadcastReceiver {@Overridepublic void onReceive(Context context, Intent intent) {String data = intent.getStringExtra(Constants.EXTENDED_DATA);Log.e(test, data);Toast.makeText(context, data, Toast.LENGTH_SHORT).show();}}}

public class RSSPullService extends IntentService {public RSSPullService() {super(RSSPullService);}@Overrideprotected void onHandleIntent(Intent workIntent) {//接收參數，做耗時的處理，處理完畢，發送BroadcatString localUrlString = workIntent.getDataString();String data = download(localUrlString);Intent localIntent = new Intent(Constants.BROADCAST_ACTION);    // Puts the status into the IntentlocalIntent.putExtra(Constants.EXTENDED_DATA, data);    // Broadcasts the Intent to receivers in this app.    LocalBroadcastManager.getInstance(this).sendBroadcast(localIntent);}private String download(String localUrlString){try{URL url = new URL(localUrlString);HttpURLConnection conn = (HttpURLConnection)url.openConnection();InputStream in = conn.getInputStream();ByteArrayOutputStream out = new ByteArrayOutputStream();byte[] buff = new byte[1024];int len = 0;while((len = in.read(buff)) != -1){out.write(buff,0,len);}in.close();return new String(out.toByteArray());}catch(Exception e){e.printStackTrace();return ;}}}

public class Constants {// Defines a custom Intent actionpublic static final String BROADCAST_ACTION = com.example.android.threadsample.BROADCAST;// Defines the key for the status extra in an Intentpublic static final String EXTENDED_DATA_STATUS = com.example.android.threadsample.STATUS;public static final String EXTENDED_DATA = com.example.android.threadsample.DATA;}

AndroidManifest.xml: