IntentService 源码分析

一般使用

1.自定义一个耗时的IntentService

public class MyIntentService extends IntentService {

   
    /**
     * Creates an IntentService.  Invoked by your subclass's constructor.
     * @param name Used to name the worker thread, important only for debugging.
     */
    public MyIntentService(String name) {
        super(name);
    }
    ...
    

    @Override
    protected void onHandleIntent(Intent intent) {
        Log.e("MyIntentService--", Thread.currentThread().getName() + "--" + intent.getStringExtra("info") );
        for(int i = 0; i < 100; i++){ //耗时操作
            Log.i("onHandleIntent--",  i + "--" + Thread.currentThread().getName());
        }
    }

}

2.启动IntentService

Intent intent = new Intent(this, MyIntentService.class);
intent.putExtra("info", "test");
startService(intent);

源码分析

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

    /**
    * 创建一个Handler 来接受处理onHandleIntent
    * 处理完耗时onHandleIntent后调用stopSelf停止掉Service
    * 所以IntentService 的执行时一次性的
    */
    private final class ServiceHandler extends Handler {
        public ServiceHandler(Looper looper) {
            super(looper);
        }

        @Override
        public void handleMessage(Message msg) {
            //处理onHandleIntent
            onHandleIntent((Intent)msg.obj);
            //停止掉Service
            stopSelf(msg.arg1);
        }
    }

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

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

    @Override
    public void onCreate() {
       
        super.onCreate();
        //创建一个HandlerThread
        HandlerThread thread = new HandlerThread("IntentService[" + mName + "]");
        //开启HandlerThread线程
        thread.start();
        //获取到HandlerThread的Looper
        mServiceLooper = thread.getLooper();
         //创建一个ServiceHandler
        mServiceHandler = new ServiceHandler(mServiceLooper);
    }

    /**
    *开始时候像mServiceHandler发送一个message
    */
    @Override
    public void onStart(@Nullable Intent intent, int startId) {
        Message msg = mServiceHandler.obtainMessage();
        msg.arg1 = startId;
        msg.obj = intent;
        mServiceHandler.sendMessage(msg);
    }

  
    @Override
    public int onStartCommand(@Nullable Intent intent, int flags, int startId) {
        onStart(intent, startId);
        return mRedelivery ? START_REDELIVER_INTENT : START_NOT_STICKY;
    }

   /**
     * 销毁service时候 停止掉mServiceLooper
     */
    @Override
    public void onDestroy() {
        mServiceLooper.quit();
    }

    /**
     * Unless you provide binding for your service, you don't need to implement this
     * method, because the default implementation returns null.
     * @see android.app.Service#onBind
     */
    @Override
    @Nullable
    public IBinder onBind(Intent intent) {
        return null;
    }

    /**
     * 模板设计模式的思想 通过子类去实现该方法来执行子类耗时操作
     */
    @WorkerThread
    protected abstract void onHandleIntent(@Nullable Intent intent);
}

通过源码可以很清楚看出: 通过调用startService 启动 IntentService，调用IntentService的onStart方法，向mServiceHandler发送一个消息，然后处理子类的onHandleIntent 然后调用stopSelf停止掉service然后调用onDestroy 然后mServiceLooper.quit()停止掉HandlerThread的looper

总结

IntentService是继承并处理异步请求的一个类，在IntentService内有一个工作线程来处理耗时操作，启动IntentService的方式和启动传统的Service一样，同时，当任务执行完后，IntentService会自动停止，而不需要我们手动去控制或stopSelf()。另外，可以启动IntentService多次，而每一个耗时操作会以工作队列的方式在IntentService的onHandleIntent回调方法中执行，并且，每次只会执行一个工作线程，执行完第一个再执行第二个。