执行后台任务并与活动通信

Question

我有一个Activity，用户可以启动一个后台网络任务。 Activity 需要与任务通信（双向）。

如果 Activity 被终止并且任务需要用户输入，则任务应该抛出重新启动 Activity 的通知。

所以。什么项目应该是“任务？服务？意图服务？

Answer 1

任务可以是广播接收器来重新启动活动。检查这个：

Android - launch app from broadcast receiver

BroadCast Receiver Documentation

Answer 2

后台任务可以是 Service、IntentService 或 AsyncTask。问题是接收用户输入，这必须在活动中完成。所以你必须告诉活动从后台线程重新启动。这可以通过广播接收器或处理程序（使用弱引用）来完成。

我将使用如下服务、活动和处理程序：

public class ActivityMain extends Activity 
{
    public static MyService myService;    
    private MyHandler myHandler = new MyHandler(this);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    protected void onResume() {
        super.onResume();
        startService(MyService.class, myConnection, null); 
    }

    private static class MyHandler extends Handler {
        private final WeakReference<ActivityMain> activityMain;

        public MyHandler(ActivityMain activity) {
            activityMain = new WeakReference<>(activity);
        }

        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case MyService.NEED_USER_INPUT:
                    final Intent i = new Intent(activityMain, ActivityMain.class);
                    i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_SINGLE_TOP);
                    startActivity(i);                   
                    break;
            }
        }
    } 

    private final ServiceConnection myConnection = new ServiceConnection()
    {
        @Override
        public void onServiceConnected(ComponentName arg0, IBinder arg1)
        {
            myService = ((MyService.UsbBinder) arg1).getService();
            myService.setHandler(myHandler);
        }

        @Override
        public void onServiceDisconnected(ComponentName arg0)
        {
            myService = null;
        }
    };

    private void startService(Class<?> service, ServiceConnection serviceConnection, Bundle extras)
    {
        if(MyService.SERVICE_CONNECTED == false)
        {
            Intent startService = new Intent(this, service);
            if(extras != null && !extras.isEmpty())
            {
                Set<String> keys = extras.keySet();
                for(String key: keys)
                {
                    String extra = extras.getString(key);
                    startService.putExtra(key, extra);
                }
            }
            startService(startService);
        }
        Intent bindingIntent = new Intent(this, service);
        bindService(bindingIntent, serviceConnection, Context.BIND_AUTO_CREATE);
    }
}

和服务：

 public class MyService extends Service
    {
        public static final int NEED_USER_INPUT = 0;
        public static boolean SERVICE_CONNECTED = false;
        private IBinder binder = new UsbBinder();
        private Context context;
        private Handler myHandler;

        @Override
        public void onCreate()
        {
            this.context = this;
        }

        @Override
        public IBinder onBind(Intent intent) 
        {
            return binder;
        }

        @Override
        public int onStartCommand(Intent intent, int flags, int startId)
        {
            return Service.START_NOT_STICKY;
        }

        @Override
        public void onDestroy()
        {
            super.onDestroy();
        }

        public void setHandler(Handler myHandler)
        {
            this.myHandler = myHandler;
        }

        public class UsbBinder extends Binder
        {
            public MyService getService()
            {
                return MyService.this;
            }
        }

        private needUserInput() //call when you need to restart activity
        {
            if(myHandler != null)
                myHandler.obtainMessage(NEED_USER_INPUT).sendToTarget();

        }
    }