IntentService 源碼分析

一般使用

1.自定義一個耗時的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++){ //耗時操作
            Log.i("onHandleIntent--",  i + "--" + Thread.currentThread().getName());
        }
    }

}

2.啓動IntentService

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

源碼分析

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

    /**
    * 創建一個Handler 來接受處理onHandleIntent
    * 處理完耗時onHandleIntent後調用stopSelf停止掉Service
    * 所以IntentService 的執行時一次性的
    */
    private final class ServiceHandler extends Handler {
        public ServiceHandler(Looper looper) {
            super(looper);
        }

        @Override
        public void handleMessage(Message msg) {
            //處理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();
        //創建一個HandlerThread
        HandlerThread thread = new HandlerThread("IntentService[" + mName + "]");
        //開啓HandlerThread線程
        thread.start();
        //獲取到HandlerThread的Looper
        mServiceLooper = thread.getLooper();
         //創建一個ServiceHandler
        mServiceHandler = new ServiceHandler(mServiceLooper);
    }

    /**
    *開始時候像mServiceHandler發送一個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;
    }

   /**
     * 銷燬service時候 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;
    }

    /**
     * 模板設計模式的思想 通過子類去實現該方法來執行子類耗時操作
     */
    @WorkerThread
    protected abstract void onHandleIntent(@Nullable Intent intent);
}

通過源碼可以很清楚看出: 通過調用startService 啓動 IntentService，調用IntentService的onStart方法，向mServiceHandler發送一個消息，然後處理子類的onHandleIntent 然後調用stopSelf停止掉service然後調用onDestroy 然後mServiceLooper.quit()停止掉HandlerThread的looper

總結

IntentService是繼承並處理異步請求的一個類，在IntentService內有一個工作線程來處理耗時操作，啓動IntentService的方式和啓動傳統的Service一樣，同時，當任務執行完後，IntentService會自動停止，而不需要我們手動去控制或stopSelf()。另外，可以啓動IntentService多次，而每一個耗時操作會以工作隊列的方式在IntentService的onHandleIntent回調方法中執行，並且，每次只會執行一個工作線程，執行完第一個再執行第二個。