IntentService通过HandlerThread单独开启一个线程来处理所有Intent请求对象

英文原文： http://developer.android.com/reference/android/app/IntentService.html

参照文章： http://android.tgbus.com/Android/tutorial/201106/355229.shtml

　 IntentService 是Service类的子类，用来处理异步请求。客户端可以通过startService(Intent)方法传递请求给 IntentService 。 IntentService 在 onCreate() 函数中通过 HandlerThread 单独开启一个线程来处理所有Intent请求对象（通过startService的方式发送过来的）所对应的任务，这样以免事务处理阻塞主线程。 执行完所一个Intent请求对象所对应的工作之后，如果没有新的Intent请求达到，则自动停止Service；否则执行下一个Intent请求所对应的任务。

　　 IntentService在处理事务时，还是采用的Handler方式，创建一个名叫 ServiceHandler 的内部Handler，并把它直接绑定到 HandlerThread所对应的子线程。  ServiceHandler把处理 一个intent所对应的事务都封装到叫做 onHandleInten t的虚函数；因此我们直接实现 虚函数 onHandleIntent ，再在里面根据Intent的不同进行不同的事务处理就可以了。

另外， IntentService默认实现了Onbind（）方法，返回值为null。

　　使用IntentService需要两个步骤：

　　 1 、写构造函数

　　 2 、 实现 虚函数 onHandleIntent ，并在里面根据Intent的不同进行不同的事务处理就可以了。

好处：处理异步请求的时候可以减少写代码的工作量，比较轻松地实现项目的需求

注意： IntentService的构造函数一定是参数为空的构造函数，然后再在其中调用 super("name")这种形式的构造函数。

因为Service的实例化是系统来完成的，而且系统是用 参数为空的 构造函数来 实例化 Service的

关于Handler和Service的更多知识请阅读《 Looper和Handler 》，《 关于Handler技术 》，《 Service简介 》，《 AIDL和Service实现两进程通信 》

Public Constructors
	IntentService(String name) Creates an IntentService.

Public Methods
IBinder	onBind(Intent intent) Unless you provide binding for your service, you don't need to implement this method, because the default implementation returns null.
void	onCreate() Called by the system when the service is first created.
void	onDestroy() Called by the system to notify a Service that it is no longer used and is being removed.
void	onStart(Intent intent, int startId) This method is deprecated. Implement onStartCommand(Intent, int, int) instead.
int	onStartCommand(Intent intent, int flags, int startId) You should not override this method for your IntentService.
void	setIntentRedelivery(boolean enabled) Sets intent redelivery preferences. If enabled is true, onStartCommand(Intent, int, int) will return START_REDELIVER_INTENT, so if this process dies before onHandleIntent(Intent)returns, the process will be restarted and the intent redelivered. If multiple Intents have been sent, only the most recent one is guaranteed to be redelivered. If enabled is false (the default), onStartCommand(Intent, int, int) will return START_NOT_STICKY, and if the process dies, the Intent dies along with it. 设置为true时， onStartCommand 返回 START_REDELIVER_INTENT，否则返回 START_NOT_STICKY 关于此的更多内容请参考《 Service简介 》

Protected Methods

abstract void

onHandleIntent(Intent intent) This method is invoked on the worker thread with a request to process. This method is invoked on the worker thread with a request to process. Only one Intent is processed at a time, but the processing happens on a worker thread that runs independently from other application logic. So, if this code takes a long time, it will hold up other requests to the same IntentService, but it will not hold up anything else. When all requests have been handled, the IntentService stops itself, so you should not call  stopSelf() . 该函数用于针对Intent的不同进行不同的事务处理就可以了.执行完所一个Intent请求对象所对应的工作之后，如果没有新的Intent请求达到， 则自动停止Service；否则 ServiceHandler会取得 下一个Intent请求传人该函数来处理其所对应的任务。

实例1

public class MyIntentService extends IntentService {
final static String TAG="robin";
 public MyIntentService() {
  super("com.lenovo.robin.test.MyIntentService");
  Log.i(TAG,this+" is constructed");
 }
 @Override
 protected void onHandleIntent(Intent arg0) {
  Log.i(TAG,"begin onHandleIntent() in "+this);
  try {
   Thread.sleep(10*1000);
  } catch (InterruptedException e) {
     e.printStackTrace();
  }
  Log.i(TAG,"end onHandleIntent() in "+this);
 }
 public void onDestroy()
 {
  super.onDestroy();
  Log.i(TAG,this+" is destroy");
 }
}

启动MyIntentServic的代码片段

Intent intent=new Intent(this,MyIntentService.class);
   startService(intent);
   startService(intent);
   startService(intent);
   

AndroidManifest.xml文件代码片段

Android:name=".MyIntentService"/>

MyIntentService.java文件运行结果

09-14 22:23:34.730: I/robin(30943): com.lenovo.robin.test.MyIntentService@40541370 is  constructed

09-14 22:23:34.730: I/robin(30943):  begin  onHandleIntent() in com.lenovo.robin.test.MyIntentService@ 40541370

09-14 22:23:44.730: I/robin(30943):  end  onHandleIntent() in com.lenovo.robin.test.MyIntentService@ 40541370

09-14 22:23:44.730: I/robin(30943):  begin  onHandleIntent() in com.lenovo.robin.test.MyIntentService@ 40541370

09-14 22:23:54.740: I/robin(30943):  end  onHandleIntent() in com.lenovo.robin.test.MyIntentService@ 40541370

09-14 22:23:54.740: I/robin(30943):  begin  onHandleIntent() in com.lenovo.robin.test.MyIntentService@ 40541370

09-14 22:24:04.739: I/robin(30943):  end  onHandleIntent() in com.lenovo.robin.test.MyIntentService@ 40541370

09-14 22:24:04.739: I/robin(30943): com.lenovo.robin.test.MyIntentService@40541370 is  destroy

IntentService源码

package android.app;


import android.content.Intent;
import android.os.Handler;
import android.os.HandlerThread;
import android.os.IBinder;
import android.os.Looper;
import android.os.Message;


public abstract class IntentService extends Service {
    private volatile Looper mServiceLooper;
    private volatile ServiceHandler mServiceHandler;
    private String mName;
    private boolean mRedelivery;


    private final class ServiceHandler extends Handler {
        public ServiceHandler(Looper looper) {
            super(looper);
        }


        @Override
        public void handleMessage(Message msg) {
            onHandleIntent((Intent)msg.obj);
            stopSelf(msg.arg1);
        }
    }


    public IntentService(String name) {
        super();
        mName = name;
    }


    public void setIntentRedelivery(boolean enabled) {
        mRedelivery = enabled;
    }


    @Override
    public void onCreate() {
        // TODO: It would be nice to have an option to hold a partial wakelock
        // during processing, and to have a static startService(Context, Intent)
        // method that would launch the service & hand off a wakelock.


        super.onCreate();
        HandlerThread thread = new HandlerThread("IntentService[" + mName + "]");
        thread.start();


        mServiceLooper = thread.getLooper();
        mServiceHandler = new ServiceHandler(mServiceLooper);
    }


    @Override
    public void onStart(Intent intent, int startId) {
        Message msg = mServiceHandler.obtainMessage();
        msg.arg1 = startId;
        msg.obj = intent;
        mServiceHandler.sendMessage(msg);
    }


    /**
     * You should not override this method for your IntentService. Instead,
     * override {@link #onHandleIntent}, which the system calls when the IntentService
     * receives a start request.
     * @see android.app.Service#onStartCommand
     */
    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        onStart(intent, startId);
        return mRedelivery ? START_REDELIVER_INTENT : START_NOT_STICKY;
    }


    @Override
    public void onDestroy() {
        mServiceLooper.quit();
    }
    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }


   protected abstract void onHandleIntent(Intent intent);

}