从片段开始服务

Question

我在从片段启动服务时遇到问题。服务已启动，但未在前台显示，我不知道为什么将 isCancelled 变量设置为 true（因此未处理 doInBackground 任务） .

当我从 FragmentActivity 启动它时，它可以工作：startService(new Intent(this, Recorder.class));。但是，当我尝试从 Fragment getActivity().startService(new Intent(getActivity(), Recorder.class)); 启动它时，它并没有按预期工作（如上所述）。

Recorder.class：

public class Recorder extends Service {

boolean isCancelled = false;


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


@Override
public int onStartCommand(Intent intent, int flags, int startId) {

    Log.v("service","started");
    Intent intent1 = new Intent(this, MainActivity.class);
    intent1.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_SINGLE_TOP);
    PendingIntent pendIntent = PendingIntent.getActivity(this, 0, intent1, 0);

    Notification noti = new NotificationCompat.Builder(this)
            .setContentTitle("Recorder")
            .setContentText("running")
            .setSmallIcon(R.drawable.ic_launcher)
            .setContentIntent(pendIntent)
            .setPriority(Notification.PRIORITY_MIN)
            .build();

    startForeground(12345, noti);


    new RecordTask().execute("http://path");

    return START_STICKY;
}

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

   isCancelled = true;
}

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


private class RecordTask extends AsyncTask<String, Void, Boolean> {
    protected Boolean doInBackground(String... StringUrls) {

     // do something
                Log.v("isCancelled", String.valueOf(isCancelled));  
                   // <-- why isCancelled = true?
                if (isCancelled) break;  

            }


        } catch (IOException e) {
            System.err.println("Caught IOException: " + e.getMessage());
        }

       return true;
    }

    protected void onProgressUpdate(Integer... progress) {

    }

    protected void onPostExecute(Boolean result) {

    }
  }

}

AddNewRecordFragment：

public class AddNewRecordFragment extends Fragment implements View.OnClickListener {

//   @Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    setRetainInstance(true);
    // Inflate the layout for this fragment
    View v = inflater.inflate(R.layout.addnewrecordfragment, container, false);

    Button b = (Button) v.findViewById(R.id.button);
    Button b2 = (Button) v.findViewById(R.id.button2);
    b.setOnClickListener(this);
    b2.setOnClickListener(this);
    return v;


}


@Override
public void onClick(View view) {
    switch (view.getId()) {
        case R.id.button:
            Log.v("start ", "clicked");
            getActivity().startService(new Intent(getActivity(), Recorder.class));

        case R.id.button2:

            getActivity().stopService(new Intent(getActivity(), Recorder.class));

            break;
    }
}

@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);
    Log.v("fragment", "onAttach");
}

@Override
public void onDetach() {
    super.onDetach();

    Log.v("fragment", "onDetach");
}

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

    Log.v("fragment", "onDestroy");
  }
}

Answer 1

您的问题与从fragment 启动service 无关。如果您将 isCancelled 设置为 true 的唯一时间是在 onDestroy 中，那么服务将按照您的意图启动，它也会在您的 AsyncTask 完成之前被杀死。看看this post。在某些情况下可以终止服务。问题是为什么会调用onDestroy。如果你在它自己的进程上运行这个service，那么service 可能会被杀死，因为你所做的只是设置一个AsyncTask。如果这与托管活动在同一进程上运行，则不完全清楚为什么要调用onDestroy（通常是因为系统需要内存，但在这种情况下我不知道这是否属实）。