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Android: save map state in google map

I have used this code before, but now I got some errors in Resuming map state. I got this code from David Gassner from his tutorial, and now I want to use it again. Confuse a little, I put some catchy message to track. LogCat report indicates an error in RESUME, starting from this line. Does anyone know how to fix this?

map.animateCamera(update); map.setMapType(mgr.getSavedMapType())

heres Code:

 @Override protected void onStop() { super.onStop(); MapStateManager mgr = new MapStateManager(this); mgr.saveMapState(mMap); Toast.makeText(this, "Map State has been save?", Toast.LENGTH_SHORT).show(); } @Override protected void onResume() { super.onResume(); MapStateManager mgr = new MapStateManager(this); CameraPosition position = mgr.getSavedCameraPosition(); if (position != null) { CameraUpdate update = CameraUpdateFactory.newCameraPosition(position); Toast.makeText(this, "entering Resume State", Toast.LENGTH_SHORT).show(); mMap.moveCamera(update); mMap.setMapType(mgr.getSavedMapType()); } } public class MapStateManager { private static final String LONGITUDE = "longitude"; private static final String LATITUDE = "latitude"; private static final String ZOOM = "zoom"; private static final String BEARING = "bearing"; private static final String TILT = "tilt"; private static final String MAPTYPE = "MAPTYPE"; private static final String PREFS_NAME ="mapCameraState"; private SharedPreferences mapStatePrefs; public MapStateManager(Context context) { mapStatePrefs = context.getSharedPreferences(PREFS_NAME, Context.MODE_PRIVATE); } public void saveMapState(GoogleMap mapMie) { SharedPreferences.Editor editor = mapStatePrefs.edit(); CameraPosition position = mapMie.getCameraPosition(); editor.putFloat(LATITUDE, (float) position.target.latitude); editor.putFloat(LONGITUDE, (float) position.target.longitude); editor.putFloat(ZOOM, position.zoom); editor.putFloat(TILT, position.tilt); editor.putFloat(BEARING, position.bearing); editor.putInt(MAPTYPE, mapMie.getMapType()); editor.commit(); } public CameraPosition getSavedCameraPosition() { double latitude = mapStatePrefs.getFloat(LATITUDE, 0); if (latitude == 0) { return null; } double longitude = mapStatePrefs.getFloat(LONGITUDE, 0); LatLng target = new LatLng(latitude, longitude); float zoom = mapStatePrefs.getFloat(ZOOM, 0); float bearing = mapStatePrefs.getFloat(BEARING, 0); float tilt = mapStatePrefs.getFloat(TILT, 0); CameraPosition position = new CameraPosition(target, zoom, tilt, bearing); return position; } public int getSavedMapType() { return mapStatePrefs.getInt(MAPTYPE, GoogleMap.MAP_TYPE_NORMAL); } }

Here is the error from logcat. I turned on only the red lines.

 > 01-07 12:51:46.145: E/AndroidRuntime(15770): FATAL EXCEPTION: main 01-07 12:51:46.145: E/AndroidRuntime(15770): java.lang.RuntimeException: Unable to resume activity {com.ourThesis.junieNegentien2015/com.ourThesis.junieNegentien2015.MainActivity}: java.lang.NullPointerException 01-07 12:51:46.145: E/AndroidRuntime(15770): at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2936) 01-07 12:51:46.145: E/AndroidRuntime(15770): at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2965) 01-07 12:51:46.145: E/AndroidRuntime(15770): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2400) 01-07 12:51:46.145: E/AndroidRuntime(15770): at android.app.ActivityThread.access$600(ActivityThread.java:162) 01-07 12:51:46.145: E/AndroidRuntime(15770): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1364) 01-07 12:51:46.145: E/AndroidRuntime(15770): at android.os.Handler.dispatchMessage(Handler.java:107) 01-07 12:51:46.145: E/AndroidRuntime(15770): at android.os.Looper.loop(Looper.java:194) 01-07 12:51:46.145: E/AndroidRuntime(15770): at android.app.ActivityThread.main(ActivityThread.java:5371) 01-07 12:51:46.145: E/AndroidRuntime(15770): at java.lang.reflect.Method.invokeNative(Native Method) 01-07 12:51:46.145: E/AndroidRuntime(15770): at java.lang.reflect.Method.invoke(Method.java:525) 01-07 12:51:46.145: E/AndroidRuntime(15770): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841) 01-07 12:51:46.145: E/AndroidRuntime(15770): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:608) 01-07 12:51:46.145: E/AndroidRuntime(15770): at dalvik.system.NativeStart.main(Native Method) 01-07 12:51:46.145: E/AndroidRuntime(15770): Caused by: java.lang.NullPointerException 01-07 12:51:46.145: E/AndroidRuntime(15770): at com.ourThesis.junieNegentien2015.MainActivity.onResume(MainActivity.java:183) 01-07 12:51:46.145: E/AndroidRuntime(15770): at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1190) 01-07 12:51:46.145: E/AndroidRuntime(15770): at android.app.Activity.performResume(Activity.java:5213) 01-07 12:51:46.145: E/AndroidRuntime(15770): at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2923) 01-07 12:51:46.145: E/AndroidRuntime(15770): ... 12 more

@Tim Castelijns, Below is a modified mode, but still not working, can you take a look?

 private SupportMapFragment mapFragment; private GoogleMap map; private Location mCurrentLocation; private GoogleApiClient mGoogleApiClient; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); setupMapIfNeeded(); mToolbar = (Toolbar) findViewById(R.id.toolbar); setSupportActionBar(mToolbar); } private void setupMapIfNeeded() { mapFragment = ((SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map)); if (mapFragment != null) { mapFragment.getMapAsync(new OnMapReadyCallback() { @Override public void onMapReady(GoogleMap map) { loadMap(map); } }); } else { Toast.makeText(this, "Error - Map Fragment was null!!", Toast.LENGTH_SHORT).show(); } } protected void loadMap(GoogleMap googleMap) { map = googleMap; if (map != null) { // Map is ready Toast.makeText(this, "Map Fragment was loaded properly!", Toast.LENGTH_LONG).show(); initListeners(); // map is loaded, trace your location mGoogleApiClient = new GoogleApiClient.Builder(this) .addApi(LocationServices.API) .addConnectionCallbacks(this) .addOnConnectionFailedListener(this) .build(); connectClient(); //calling resume state resumeState(map); } else { Toast.makeText(this, "Error - Map was null!!", Toast.LENGTH_SHORT).show(); } } protected void connectClient() { // Connect the client. if (isGooglePlayServicesAvailable() && mGoogleApiClient != null) { mGoogleApiClient.connect(); Toast.makeText(this, "Google API Client successfully connected", Toast.LENGTH_LONG).show(); } } /* * Called when the Activity becomes visible. */ @Override protected void onStart() { super.onStart(); connectClient(); } public void resumeState(GoogleMap googleMap) { map = googleMap; MapStateManager mgr = new MapStateManager(this); CameraPosition position = mgr.getSavedCameraPosition(); if (position != null) { CameraUpdate update = CameraUpdateFactory.newCameraPosition(position); Toast.makeText(this, "entering Resume State", Toast.LENGTH_LONG).show(); map.moveCamera(update); map.setMapType(mgr.getSavedMapType()); } } /* * Called when the Activity is no longer visible. */ @Override protected void onPause() { super.onPause(); MapStateManager mgr = new MapStateManager(this); mgr.saveMapState(map); Toast.makeText(this, "Map State has been save?", Toast.LENGTH_LONG).show(); } @Override protected void onResume() { super.onResume(); setupMapIfNeeded(); } @Override public void onConnected(Bundle dataBundle) { // Display the connection status Location location = LocationServices.FusedLocationApi.getLastLocation(mGoogleApiClient); if (location != null) { Toast.makeText(this, "GPS location was found!", Toast.LENGTH_SHORT).show(); LatLng latLng = new LatLng(location.getLatitude(), location.getLongitude()); CameraUpdate cameraUpdate = CameraUpdateFactory.newLatLngZoom(latLng, 16); map.animateCamera(cameraUpdate); /*startLocationUpdates();*/ } else { Toast.makeText(this, "Current location was null, enable GPS on your mobile!", Toast.LENGTH_SHORT).show(); } } private void initListeners() { map.setMapType(GoogleMap.MAP_TYPE_HYBRID); map.getUiSettings().setZoomControlsEnabled(true); map.setMyLocationEnabled(true); map.setOnMarkerClickListener(null); map.setOnMapLongClickListener(null); map.setOnInfoWindowClickListener(null); map.setOnMapClickListener(null); map.setTrafficEnabled(true); map.setOnMapLongClickListener(this); map.setOnMapClickListener(this); map.setPadding(0, 80, 0, 0); }
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3 answers

The problem is that your mMap is null when resuming, and then you cannot use mMap.moveCamera(); , for example, causing your application to crash.

The solution for this is to check if you need to configure the card before trying to use it again.

I changed your code a bit to check if you need to configure the map in both onCreate and onResume. Please note that I use onPause instead of onStop, because it is an analogue of onResume.

 private GoogleMap mMap; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_maps); setupMapIfNeeded(); } private void setupMapIfNeeded() { // Obtain the SupportMapFragment and get notified when the map is ready to be used. if (mMap == null) { SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager() .findFragmentById(R.id.map); mapFragment.getMapAsync(this); } } @Override public void onMapReady(GoogleMap googleMap) { mMap = googleMap; MapStateManager mgr = new MapStateManager(this); CameraPosition position = mgr.getSavedCameraPosition(); if (position != null) { CameraUpdate update = CameraUpdateFactory.newCameraPosition(position); Toast.makeText(this, "entering Resume State", Toast.LENGTH_SHORT).show(); mMap.moveCamera(update); mMap.setMapType(mgr.getSavedMapType()); } } @Override protected void onPause() { super.onPause(); MapStateManager mgr = new MapStateManager(this); mgr.saveMapState(mMap); Toast.makeText(this, "Map State has been save?", Toast.LENGTH_SHORT).show(); } @Override protected void onResume() { super.onResume(); setupMapIfNeeded(); }

MapstateManager is exactly the same.

 public class MapStateManager { private static final String LONGITUDE = "longitude"; private static final String LATITUDE = "latitude"; private static final String ZOOM = "zoom"; private static final String BEARING = "bearing"; private static final String TILT = "tilt"; private static final String MAPTYPE = "MAPTYPE"; private static final String PREFS_NAME ="mapCameraState"; private SharedPreferences mapStatePrefs; public MapStateManager(Context context) { mapStatePrefs = context.getSharedPreferences(PREFS_NAME, Context.MODE_PRIVATE); } public void saveMapState(GoogleMap mapMie) { SharedPreferences.Editor editor = mapStatePrefs.edit(); CameraPosition position = mapMie.getCameraPosition(); editor.putFloat(LATITUDE, (float) position.target.latitude); editor.putFloat(LONGITUDE, (float) position.target.longitude); editor.putFloat(ZOOM, position.zoom); editor.putFloat(TILT, position.tilt); editor.putFloat(BEARING, position.bearing); editor.putInt(MAPTYPE, mapMie.getMapType()); editor.commit(); } public CameraPosition getSavedCameraPosition() { double latitude = mapStatePrefs.getFloat(LATITUDE, 0); if (latitude == 0) { return null; } double longitude = mapStatePrefs.getFloat(LONGITUDE, 0); LatLng target = new LatLng(latitude, longitude); float zoom = mapStatePrefs.getFloat(ZOOM, 0); float bearing = mapStatePrefs.getFloat(BEARING, 0); float tilt = mapStatePrefs.getFloat(TILT, 0); CameraPosition position = new CameraPosition(target, zoom, tilt, bearing); return position; } public int getSavedMapType() { return mapStatePrefs.getInt(MAPTYPE, GoogleMap.MAP_TYPE_NORMAL); } }
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If you just want to save and restore the camera position between orientation changes, you can just save the CameraPosition instance directly in your saveInstanceState package. CameraPosition implements ReflectedParcelable , so this should work.

 @Override public void onSaveInstanceState(Bundle outState) { super.onSaveInstanceState(outState); if (googleMap != null) { outState.putParcelable(STATE_KEY_MAP_CAMERA, googleMap.getCameraPosition()); } }
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mapFragment.setRetainInstance(true); You can use it in onCreate to save the state of a map fragment.

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Source: https://habr.com/ru/post/1240003/

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