1,用户离开activity后,仍需要继续工作,例如从网络下载文件,播放音乐.
2,无论activity出现或离开,都需要持续工作,例如网络聊天应用.
3,连接网络服务,正在使用一个远程API提供的服务.
4,定时触发的任务
1.因为IntentService是Service子类,所以也需要在manifest中声明服务
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.intentservicedemo"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="21" />
<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name=".MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<service android:name="com.example.intentservicedemo.ServiceDownloader"></service>
</application>
</manifest>
2,新建 ServiceDownloader 继承自 IntentService
public class ServiceDownloader extends IntentService {
//避免出现命名重复，将类的命名空间加在前面
public static final String EXTRA_MESSAGER="com.wei.android.learning.ServiceDownloader.EXTRA_MESSAGER";
public ServiceDownloader() {
super("ServiceDownloader");
}
//命令模式的服务由client请求服务,
private HttpClient client=null;
int result ;
private Intent mIntent;
//client通过startService请求服务时,如果没有开启,则会首先执行onCreate(),在这里做一些初始化的工作,onCreate是在主线程中运行
@Override
public void onCreate() {
super.onCreate();
client=new DefaultHttpClient();
}
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
return super.onStartCommand(intent, flags, startId);
}
//再收到客户端命令,处理完onStartCommand()后执行,onHandleIntent()是在后台线程中运行
@Override
protected void onHandleIntent(Intent i) {
this.mIntent=i;
result = Activity.RESULT_CANCELED;
HttpGet get=new HttpGet(i.getData().toString());
ResponseHandler<byte[]> responseHandler =new ByteArrayResponseHandler();
try {
byte[] responseByte=client.execute(get,responseHandler);
File output=new File(Environment.getExternalStorageDirectory(),i.getData().getLastPathSegment());
if(output.exists()){
output.delete();
}
FileOutputStream fos=new FileOutputStream(output.getPath());
fos.write(responseByte);
fos.close();
result=Activity.RESULT_OK;
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
Bundle extras=i.getExtras();
if(extras!=null){
Messenger messenger =(Messenger) extras.get(EXTRA_MESSAGER);
Message msg=Message.obtain();
msg.arg1=result;
try {
messenger.send(msg);
} catch (RemoteException e) {
e.printStackTrace();
}
}
}
@Override
public void onDestroy() {
Bundle extras=mIntent.getExtras();
if(extras!=null){
Messenger messenger =(Messenger) extras.get(EXTRA_MESSAGER);
Message msg=Message.obtain();
msg.arg1=result;
try {
messenger.send(msg);
} catch (RemoteException e) {
e.printStackTrace();
}
}
client.getConnectionManager().shutdown();
super.onDestroy();
}
private class ByteArrayResponseHandler implements ResponseHandler<byte[]>{
@Override
public byte[] handleResponse(HttpResponse response)
throws ClientProtocolException, IOException {
StatusLine statusLine=response.getStatusLine();
if(statusLine.getStatusCode()>300){
throw new HttpResponseException(statusLine.getStatusCode(),statusLine.getReasonPhrase());
}
HttpEntity entity=response.getEntity();
if(entity==null){
return null;
}
return EntityUtils.toByteArray(entity);
}
}
}
3,在客户端调用服务,开启下载任务,并且在下载完成时,可以收到下载完成的消息
public class MainActivity extends ActionBarActivity {
Button btn_start;
Button btn_stop;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btn_start=(Button) findViewById(R.id.btn_start);
btn_stop=(Button) findViewById(R.id.btn_stop);
btn_start.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
startDownLoader();
}
});
btn_stop.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View arg0) {
stopDownLoader();
}
});
}
private void startDownLoader(){
Intent intent=new Intent(this, ServiceDownloader.class);
intent.setData(Uri.parse("http://commonsware.com/Android/excerpt.pdf"));
intent.putExtra(ServiceDownloader.EXTRA_MESSAGER,new Messenger(mh));
startService(intent);
}
private Handler mh=new Handler(){
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
//下载完成后,将取消服务按钮失效
switch (msg.arg1) {
case Activity.RESULT_OK:
Toast.makeText(MainActivity.this, "Result : OK " , Toast.LENGTH_LONG).show();
break;
case Activity.RESULT_CANCELED:
Toast.makeText(MainActivity.this, "Result : Cancel " , Toast.LENGTH_LONG).show();
break;
default:
break;
}
}
};
private void stopDownLoader(){
stopService(new Intent(this, ServiceDownloader.class));
}
}
4,activity_main.xml
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context="com.example.intentservicedemo.MainActivity" >
<Button
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="start"
android:id="@+id/btn_start"
/>
<Button
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="stop"
android:id="@+id/btn_stop"
/>
</LinearLayout>