Android传感器侦听器未响应，且未在Backstack中添加和删除片段

Question

I have an Android handheld app and an Android wear app that both use fragments and listen for shaking gestures using the sensor manager and custom listeners that I have made.

On each app I have a main fragment that contains a menu and a sensor manager with my custom listeners registered. When a user selects a menu item, the main fragment is replaced with the menu item fragment (the menu item fragment has it's own sensor manager with different custom listeners), and when you go back from the menu item fragment, popBackStackImmediate() is called to return to the main fragment.

This works perfectly on the handheld app, and on the wear app it works fine too, for a while; if you open the menu item fragment and then go back to the main fragment continuously, after 5 or 6 times doing this the sensor listeners become sluggish, and eventually stop working. Does anyone know what might be causing this?

This is how I handle registering and unregistering the listeners with the sensorManager in each of the fragments:

Main Fragment

public class MainFragment extends Fragment {

    private MainWearActivity mMainWearActivity;
    View view;

    private SensorManager mSensorMgr;
    private ShakeListener shakeListener;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mMainWearActivity = (MainWearActivity) getActivity();
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        view = inflater.inflate(R.layout.fragment_main, container, false);

        mSensorMgr = (SensorManager) mMainWearActivity.getSystemService(Activity.SENSOR_SERVICE);
        shakeListener = new ShakeListener();

        shakeListener.setOnShakeListener(new OnShakeListener() {
            @Override
            public void onShake() {
                    MenuItemFragment mif = new MenuItemFragment();
                    mMainWearActivity.replaceFragment(mif, "menuFrag");
                }
            }
        });

        startListening();
        return view;
    }

    @Override
    public void onPause() {
        stopListening();
        super.onPause();
    }

    @Override
    public void onResume() {
        super.onResume();
        startListening();
    }

    @Override
    public void onDestroyView() {
        stopListening();
        super.onDestroyView();
    }


    private void startListening(){
        mSensorMgr.registerListener(shakeListener, mSensorMgr.getDefaultSensor(Sensor.TYPE_GYROSCOPE), SensorManager.SENSOR_DELAY_GAME);
    }

    private void stopListening(){
        mSensorMgr.unregisterListener(shakeListener);
    }
}

Menu Item Fragment

public class MenuItemFragment extends Fragment {

    private View view;
    private MainWearActivity mMainWearActivity;
    private SensorManager mSensorMgr;
    private FragmentManager fManager;
    private ShakeListener shakeListener;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mMainWearActivity = (MainWearActivity) getActivity();
        fManager = getFragmentManager();
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        view = inflater.inflate(R.layout.fragment_menu_item, container, false);

        mSensorMgr = (SensorManager) mMainWearActivity.getSystemService(Activity.SENSOR_SERVICE);
        shakeListener = new ShakeListener();

        shakeListener.setOnShakeListener(new OnShakeListener() {
            @Override
            public void onShake() {
                fManager.popBackStackImmediate();
            }
        });

        startListening();
        return view;
    }

    @Override
    public void onPause() {
        stopListening();
        super.onPause();
    }

    @Override
    public void onResume() {
        super.onResume();
        startListening();
    }

    @Override
    public void onDestroyView() {
        stopListening();
        super.onDestroyView();
    }

    private void startListening(){
        mSensorMgr.registerListener(shakeListener, mSensorMgr.getDefaultSensor(Sensor.TYPE_GYROSCOPE), SensorManager.SENSOR_DELAY_GAME);
    }

    private void stopListening(){
        mSensorMgr.unregisterListener(shakeListener);
    }
}

Method to Replace Fragment

public void replaceFragment(Fragment frag, String fragTag) {
    mFragmentTransaction = mFragmentManager.beginTransaction();
    mFragmentTransaction.replace(R.id.fragmentContainer, frag, fragTag);
    mFragmentTransaction.addToBackStack(null);
    mFragmentTransaction.commit();
}

Like I say, this set up works fine on the handheld app, but on the watch the sensor listener malfunctions after loading and going back from the menu item fragment. Any help would be greatly appreciated, thanks.

EDIT

So as per the suggestions, I have moved my fragments to the MainActivity class so that they can be re-used. I have also changed the replaceFragment method to this instead:

public void replaceFragment(Fragment frag, String fragTag) {
    Fragment currentFrag = mFragmentManager.findFragmentById(R.id.fragmentContainer);
    mFragmentManager.beginTransaction()
            .remove(currentFrag)
            .add(R.id.fragmentContainer, frag, fragTag)
            .addToBackStack(null)
            .commit();
}

I have placed Logs in the onResume() and onPause() methods of the MainFragment and the MenuItemFragments to check whether they are being called and can confirm that they are.

I have also moved the SensorManager to the MainActivity and use that to register/unregister listeners, which themselves have been moved to the OnCreate() method of each fragment so that new listeners are not being created every time the view is created.

After all this the same problem persists. I can go into a MenuItemFragment and back to the MainFragment maybe 8-10 times before the listeners/sensors stop working. I have also looked at the memory tab of AndroidMonitor in Android Studio as I am going into and out of the fragments, and it appears to fill up steadily until the allocated amount reaches about 5MB before the sensors crash.

Answer 1

My testing indicates that onResume() and onPause() don't get called by FragmentTransaction.replace() , so it wouldn't surprise me if they also don't get called when that transaction is popped off the back stack. You can confirm this in your own code by adding some logging to your onResume() and onPause() methods and watching when they get called.

If this is indeed the case, the workaround I've used is to call FragmentTransaction.remove() and add() instead of replace() . So your replaceFragment method body would then look like this:

Fragment currentFrag = fragMgr.findFragmentById(R.id.fragmentContainer);
mFragmentManager.beginTransaction()
    .remove(currentFrag)
    .add(R.id.fragmentContainer, frag, fragTag)
    .addToBackStack(null)
    .commit();