IntentService原理

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最新推荐文章于 2025-01-24 08:00:10 发布

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分类专栏： android 中级

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本文介绍了Android中的IntentService组件，它是一种简化任务队列处理模式的服务类。文章详细解析了IntentService如何通过创建独立的工作线程处理请求，并在完成任务后自动停止自身。

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介绍
* IntentService is a base class for {@link Service}s that handle asynchronous
* requests (expressed as {@link Intent}s) on demand.  Clients send requests
* through {@link 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.
*
* <p>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 {@link #onHandleIntent(Intent)}.  IntentService
* will receive the Intents, launch a worker thread, and stop the service as
* appropriate.
*
* <p>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.

看以下IntentService 的oncreate方法干了什么

首先开了一个线程，其次创建了这个线程的Looper，然后又把创建的Looper与Handler进行了绑定。

@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);
}

再看一下onStart()方法，通过mServiceHandler发送消息

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

接下来再看一下自定义的ServiceHandler的实现。收到消息后调用了抽象方法onHandlerIntent();这个方法执行完毕会调用

stopSelf()终止本服务。

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startService开始

创建线程，

创建该线程的Looper,

把自定义Handler与Looper绑定

在StartComment通过handler发送消息

在handlerMessage中处理消息回调onHandleIntent