什么是IntentService? （本文转自 ）
官方的解释是:
Services that handle asynchronous requests (expressed as
Intents) on demand. Clients send requests through
android.content.Context.startService(Intent) calls; the service is started as needed, handles each Intent in turn using a worker thread, and stops itself when it runs out of work.
This "work queue processor" pattern is commonly used to offload tasks from an application's main thread. The IntentService class exists to simplify this pattern and take care of the mechanics. To use it, extend IntentService and implement
onHandleIntent(Intent). IntentService will receive the Intents, launch a worker thread, and stop the service as appropriate.
All requests are handled on a single worker thread -- they may take as long as necessary (and will not block the application's main loop), but only one request will be processed at a time.
意思是说:IntentService是一个通过
Context.startService(Intent)启动可以处理异步请求的Service,使用时你只需要继承IntentService和重写其中的
onHandleIntent(Intent)方法接收一个Intent对象,在适当的时候会停止自己(一般在工作完成的时候). 所有的请求的处理都在一个工作线程中完成,它们会交替执行(但不会阻塞主线程的执行),一次只能执行一个请求.(**本人修改了原文的一些翻译)
下面是要分析的源码:
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);
}
}
从源码可以分析出:
IntentService 实际上是Looper,Handler,Service 的集合体,他不仅有服务的功能,还有处理和循环消息的功能.
下面是onCreate()的源码:
@Override
public
void onCreate() {
super.onCreate();
HandlerThread thread =
new HandlerThread(
"IntentService[" + mName +
"]");
thread.start();
mServiceLooper = thread.getLooper();
mServiceHandler =
new ServiceHandler(mServiceLooper);
}
分析:IntentService创建时就会创建Handler线程(HandlerThread)并且启动,然后再得到当前线程的Looper对象来初始化IntentService的mServiceLooper,接着创建mServicehandler对象.
下面是onStart()的源码:
@Override
public
void onStart(Intent intent,
int startId) {
Message msg = mServiceHandler.obtainMessage();
msg.arg1 = startId;
msg.obj = intent;
mServiceHandler.sendMessage(msg);
}
@Override
public
void handleMessage(Message msg) {
onHandleIntent((Intent)msg.obj);
stopSelf(msg.arg1);
}
当所有的工作执行完后:就会执行onDestroy方法,源码如下:
@Override
public
void onDestroy() {
mServiceLooper.quit();
}
服务结束后调用这个方法 mServiceLooper.quit()使looper停下来.
