Google Maps Fragment替换当前片段

Question

Background:
Create an app that will center on the user's location and allow for them to text their location to contacts. To do this, we need a simple credential check and server address to test on in the preferences.

Issue:
Whenever the user navigates from the original map fragment that shows their location with a marker, the proper map type (hybrid), etc. to another fragment and then wants to return to the map fragment, it defaults to LatLng 0,0 and a generic map (no indication of user location for example).

My initial thought was to try and save the state of the map fragment upon switching to another fragment and reload that when popping the other fragment from the stack. However I then thought it might be simpler to just replace the current fragment in the MainActivity whenever I need to switch. So on opening the app, MainActivity creates a new MapFragment then replaces it with a Preferences Fragment and when 'saving' creates a new MapFragment to replace the current fragment with. Thought this might fix my problem as on initial load the map functions like I want.

The code for MFragment that contains the Map Fragment:

public class MFragment extends Fragment implements android.location.LocationListener,
                    GooglePlayServicesClient.ConnectionCallbacks, 
                    GooglePlayServicesClient.OnConnectionFailedListener{

private final static int CONNECTION_FAILURE_RESOLUTION_REQUEST = 9000;
private static GoogleMap map;
private static LocationClient lClient;
private final static String TAG = "MFragment";
private String provider;
private Location loc;
private LocationManager lManager;
private LatLng currentLatLng;
private final long MIN_TIME = 1000;
private final float MIN_DIST = 10;
private Update updateMarkers = new Update();
private View view;
private MapFragment mFrag;

public void onCreate(Bundle savedInstanceState){
    super.onCreate(savedInstanceState);
    mFrag = MapFragment.newInstance();
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
        Bundle savedInstanceState)  {
    super.onCreateView(inflater, container, savedInstanceState);
    //sets the layout for this fragment
    view = inflater.inflate(R.layout.fragment_map, container, false);
    //insert MapFragment into this Fragment 
    getActivity().getFragmentManager().beginTransaction()
            .replace(R.id.mapview, mFrag)
            .commit();
    //get a handle on the map from the MapFragment
//      map = mFrag.getMap();
    //instantiates the location manager
    lManager = (LocationManager) getActivity().getSystemService(Context.LOCATION_SERVICE);
    //instantiate the location client
    lClient = new LocationClient(getActivity(), this, this);
    lClient.connect();
    //run through initialization of all objects 
    setUpMapIfNeeded();
    Log.d(TAG, "Successfully created MFragment");
    return view;
}

/**
 * instantiates map from the MapFragment if map is null.  
 */
private void setUpMapIfNeeded() {
    if (getActivity() != null && getActivity().getFragmentManager() != null &&
            map == null)    {
        map = mFrag.getMap();
        Log.d(TAG, "Map generated.");
        setUpMap();
    }   else if (lClient.isConnected()) {
        updateMap();
    }   else    {
        setUpMap();
    }
}

/**
 * sets up the location data for the map.  conditional clause so that the GPS doesn't crash
 * if the app can't get a location straight away.
 */
private void setUpMap() {
    if (map != null) {
        map.setMyLocationEnabled(true);
        map.setMapType(GoogleMap.MAP_TYPE_HYBRID);
        Criteria crit = new Criteria();
        provider = lManager.getBestProvider(crit, false);
        if (lManager.isProviderEnabled(LocationManager.GPS_PROVIDER)) {
            loc = lManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);
        }   else {
            loc = lManager.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
        }
        lManager.requestLocationUpdates(provider, MIN_TIME, MIN_DIST, this);

    }
}


protected void updateMap()  {
    if (servicesConnected())    {
        map.clear();
        currentLatLng = new LatLng(this.loc.getLatitude(), this.loc.getLongitude());
        map.animateCamera(CameraUpdateFactory.newLatLngZoom(currentLatLng, 14));
        map.addMarker(new MarkerOptions()
                    .position(currentLatLng)
                    .title("You"));
        map.setOnMarkerClickListener(new OnMarkerClickListener() {

            @Override
            public boolean onMarkerClick(Marker m) {
                SMSFragment sFrag = new SMSFragment();
                sFrag.setMarker(m);
                getActivity().getFragmentManager().beginTransaction()
                    .replace(android.R.id.content, sFrag)
                    .commit();
                return false;
            }
        });

    }
}

/**
 * checks for connection to google play services
 * @return
 */
private boolean servicesConnected() {
    int resultCode = GooglePlayServicesUtil
            .isGooglePlayServicesAvailable(getActivity().getApplicationContext());
    if (ConnectionResult.SUCCESS == resultCode) {
        Log.d(TAG, getString(R.string.play_available));
        return true;
    } else {
        if (GooglePlayServicesUtil.isUserRecoverableError(resultCode))  {
            GooglePlayServicesUtil
                .getErrorDialog(resultCode, getActivity(), 
                    CONNECTION_FAILURE_RESOLUTION_REQUEST).show();
        }   else    {
            Log.i(TAG, "This device is not supported");
        }
        return false;
    }
}

@Override
public void onConnectionFailed(ConnectionResult connectionResult) {
    if (connectionResult.hasResolution())   {
        try {
            connectionResult
                .startResolutionForResult(getActivity(), CONNECTION_FAILURE_RESOLUTION_REQUEST);
        }   catch (IntentSender.SendIntentException e)  {
            e.printStackTrace();
        }
    }   else    {
        Toast.makeText(getActivity(), R.string.connect_failed, Toast.LENGTH_SHORT).show();
    }
}

/**
 * Called after location client connects
 */
@Override
public void onConnected(Bundle arg0) {
    updateMap();
}

/**
 * simple display message after disconnecting.
 */
@Override
public void onDisconnected() {
    Toast.makeText(getActivity(), R.string.disconnected, Toast.LENGTH_SHORT).show();
}


public void onStart()   {
    super.onStart();
    lClient.connect();
    setUpMapIfNeeded();
}

public void onResume()  {
    super.onResume();
    lClient.connect();
    setUpMapIfNeeded();
}

public void onPause()   {
    lClient.disconnect();
    super.onPause();
}

public void onStop()    {
    lClient.disconnect();
    super.onStop();
}

public void onDestroy() {
    lClient.disconnect();
    super.onDestroy();
}

@Override
public void onLocationChanged(Location location) {
    this.loc = location;
    updateMap();
}

@Override
public void onProviderDisabled(String provider) {
    // TODO Auto-generated method stub

}

@Override
public void onProviderEnabled(String provider) {
    // TODO Auto-generated method stub

}

@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
    // TODO Auto-generated method stub

}


public void updateMarkers(List<Record> records){
    //update map with markers corresponding to each latitude, longitude passed back from records
    for (Record r : records){
        map.addMarker( new MarkerOptions()
                .position(new LatLng(r.getValueOfLatitude(), r.getValueOfLongitude())));
    }
}

private class Update extends AsyncTask<Void, Void, Boolean> {

    private List<Record> records;

    protected Update()  {
        super();
        records = new ArrayList<Record>();
    }

    @Override
    protected Boolean doInBackground(Void... params) {
        Connect conn = new Connect(getActivity());
        try {
            records = conn.getAll();
            return true;
        } catch (IOException e) {
            e.printStackTrace();
        }
        return false;
    }

    protected void onPostExecute(Boolean result)    {
        if (result) {
            updateMarkers(records);
        }   else    {
            Toast.makeText(getActivity(), R.string.rec_fail, Toast.LENGTH_SHORT).show();
        }
    }
}
}

And an example of replacing the Fragment from another Fragment (From PrefsFragment to MFragment):

    register = (Button) v.findViewById(R.id.register);

    save.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            saveToPreferences(v);
            ((MainActivity)getActivity()).replaceFragment();
        }
    });

    register.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            getActivity().getFragmentManager().beginTransaction()
                .replace(android.R.id.content, new RegFragment())
                .commit();
        }
    });

    return v;
}

the save button calls a method in MainActivity to replace the current fragment with a MapFragment as an attempted work-around but doesn't function like I was hoping and using the similar method for the register button using FragmentManager doesn't fix the Map issue either.

Any help is appreciated.

Answer 1

Don't put a fragment inside another fragment unless you really need to. If you choose to do so, you may not use the FragmentManager of the Activity like you do. Instead you must use the child fragment manager of the container fragment to create the fragment transaction that will insert the child fragment by calling getChildFragmentManager() .

This is supported since API level 17 (Android 4.2) or using the most recent Android Support Library. I suggest you to always use the support library by default.