IntentService,可以看做是Service和HandlerThread的結合體,在完成了使命之後會自動停止,適合需要在工作線程處理UI無關任務的場景。
IntentService內部使用的是HandlerThread 和Handler,
HandlerThread是在Thread的run方法中初始化loop,調用Loop.prepare(),Loop.loop(),線程中有了loop,就可以在該線程中創建handler了,通過Handler來處理任務;
回到IntentService中,它是service,所以比一般的線程優先級高,所以可以執行高優先級的任務;在onCreate()中實例化handlerThread,利用HandlerThread創建handler,然後通過handler發送消息來執行後臺任務。
不建議通過 bindService() 啓動 IntentService,因爲onBind()默認return null;
第一次啓動IntentService,會調用onCreate(),onStartCommand,後面再次啓動,只會調用onStartCommand(),在onStartCommand()方法中
/** * 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(@Nullable Intent intent, int flags, int startId) { onStart(intent, startId); return mRedelivery ? START_REDELIVER_INTENT : START_NOT_STICKY; } 會調用onStart(intent, startId);
@Override public void onStart(@Nullable Intent intent, int startId) { Message msg = mServiceHandler.obtainMessage(); msg.arg1 = startId; msg.obj = intent; mServiceHandler.sendMessage(msg); }
serviceHandler繼承與handler,
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); } }
onHandleIntent是個抽象方法,所以在子類中,實現此方法,也就是後臺任務邏輯在此方法中執行 ;