Android中使用IntentService运行后台任务

IntentService提供了一种在后台线程中运行任务的方式，适合处理运行时间较长的后台任务。

长处：

（1）IntentService执行在单独的线程中。不会堵塞UI线程

（2）IntentService不受生命周期的影响

缺点：

（1）不能与UI直接进行交互，能够用Broadcast

（2）顺序运行请求，第二个请求仅仅有在第一个请求运行完以后才干运行

（3）请求不能被中断

使用IntentService的步骤：

（1）在Activity中通过startService启动service，并传递參数。

（2）Service中接收參数，做耗时的处理。处理完成，发送Broadcat，并把处理结果传递出来

（3）Activity中注冊BroadcastReceiver，监听广播，更新UI。

看一个样例：

public class MainActivity extends Activity {

@Override
protected 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() {
@Override
public void onClick(View v) {//通过startService启动service。并传递參数。
Intent mServiceIntent = new Intent(MainActivity.this,RSSPullService.class);
mServiceIntent.setData(Uri.parse("http://www.baidu.com/"));
MainActivity.this.startService(mServiceIntent);
}
});
//注冊BroadcastReceiver。监听广播
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 filters
LocalBroadcastManager.getInstance(this).registerReceiver(mDownloadStateReceiver, statusIntentFilter);

}

private class DownloadStateReceiver extends BroadcastReceiver {
@Override
public 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");
}

@Override
protected void onHandleIntent(Intent workIntent) {//接收參数。做耗时的处理。处理完成。发送Broadcat
String localUrlString = workIntent.getDataString();
String data = download(localUrlString);
Intent localIntent = new Intent(Constants.BROADCAST_ACTION);
// Puts the status into the Intent
localIntent.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 action
public static final String BROADCAST_ACTION = "com.example.android.threadsample.BROADCAST";

// Defines the key for the status "extra" in an Intent
public static final String EXTENDED_DATA_STATUS = "com.example.android.threadsample.STATUS";

public static final String EXTENDED_DATA = "com.example.android.threadsample.DATA";

}

AndroidManifest.xml:

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.android.intentservicedemo"
android:versionCode="1"
android:versionName="1.0" >

<uses-sdk
android:minSdkVersion="11"
android:targetSdkVersion="17" />

<!-- Requires this permission to download RSS data from Picasa -->
<uses-permission android:name="android.permission.INTERNET" />

<!--
Defines the application.
-->
<application
android:icon="@drawable/icon"
android:label="@string/app_name">

<activity
android:name="com.example.android.intentservicedemo.MainActivity"
android:label="@string/activity_title" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>

<!--
No intent filters are specified, so android:exported defaults to "false". The
service is only available to this app.
-->
<service
android:name="com.example.android.intentservicedemo.RSSPullService"
android:exported="false"/>

</application>

</manifest>

參考：http://developer.android.com/training/run-background-service/index.html