How to save a marker using SharedPreferences

Question

I'm using Mapsforge Library to develop my app. In the map, you can create your own mark by long press on the map.

Now i would like to save this marker using sharedPreferences, so if the user close the app and repp, the marker still there. Unfortunately, i have not found such information around the web on how to do so. I have found some information on how to do it using Google maps, but google map have different functions. Can anyone help me how to do it?

this is how i add the mark on the map. the code is in the OnCreate part:

 myListOverlay = new ListOverlay();
 myOverlayItems = myListOverlay.getOverlayItems();
 mapView.getOverlays().add(myListOverlay);

 mGestureDetector = new GestureDetector(this, new GestureDetector.SimpleOnGestureListener() {

            @Override
            public void onLongPress(MotionEvent e) {

                float x = e.getX();
                float y = e.getY();


                if (e.getAction() == MotionEvent.ACTION_DOWN) {

                    GeoPoint gPt = mapView.getProjection().fromPixels((int) x,   (int)y);

                        myMarker = createMarker(gPt, R.drawable.ic_location);
                        myOverlayItems.add(myMarker);
                        byte viewMarker =   mapView.getMapViewPosition().getZoomLevel();
                        mapView.getMapViewPosition().setZoomLevel(viewMarker); 



                     }

                }

            public boolean onSingleTapConfirmed(MotionEvent motionEvent) {
                myOverlayItems.remove(myMarker);
                byte viewMarker =   mapView.getMapViewPosition().getZoomLevel();
                mapView.getMapViewPosition().setZoomLevel(viewMarker);
                return true; 
            };
            }
        );

        mapView.setOnTouchListener(new OnTouchListener() {

            @Override
            public boolean onTouch(View v0, MotionEvent e) {
                // Only fires if Mapview touched
                return mGestureDetector.onTouchEvent(e);
            }


        }); 

Thanks to zcg7009 i was able to let the shared preferences work, but still a problem. This is the code:

in onCreate

if((prefs.contains("Lat")) && (prefs.contains("Lon"))){   

            String lat = prefs.getString("Lat",""); //with "" it throw error " Invalid "" ", if i put "0" the marker appear somewhere in the map
            String lng = prefs.getString("Lng", ""); 

            GeoPoint l =new GeoPoint(Double.parseDouble(lat),Double.parseDouble(lng));
            myMarker = createMarker(l, R.drawable.ic_location);
            myOverlayItems.add(myMarker);
                byte viewMarker =   this.mapView.getMapViewPosition().getZoomLevel();
                this.mapView.getMapViewPosition().setZoomLevel(viewMarker); 
                this.mapView.getMapViewPosition().setCenter(l);
        }

In the LongPress method

                            float x = e.getX();
                    float y = e.getY();

                    GeoPoint gPt = mapView.getProjection().fromPixels((int)x,   (int)y);

                    myMarker = createMarker(gPt, R.drawable.ic_location);
                    myOverlayItems.add(myMarker);
                    byte viewMarker =   mapView.getMapViewPosition().getZoomLevel();
                    mapView.getMapViewPosition().setZoomLevel(viewMarker);  
                    prefs.edit().putString("Lat",String.valueOf(gPt.latitude)).commit();
                    prefs.edit().putString("Lon",String.valueOf(gPt.latitude)).commit();

the problem is in the second and third line of the code inside onCreate. If i use "" it throw the error invalid "", if i use "0" , the marker appear somewhere on the map. How can solve this?

Answer 1

Do something like this, in your class add

private SharedPreferecnes prefs;

Then when your activity is destroyed

@Override
public void onDestroy(){
     prefs.putDouble("marker_latitude", marker.getPosition().latitude);
     prefs.putDouble("marker_longitude", marker.getPosition().longitude);
}

Then in onCreate

prefs = this.getSharedPreferences("com.smashing_boxes.taskproject",
            Context.MODE_PRIVATE);
double latitude = prefs.getDouble("marker_latitude", -1.0);
double longitude = prefs.getDouble("marker_latitude", -1.0);

if(latitude != -1.0 && longitude != -1.0){
     Marker marker = mapView.addMarker(new MarkerOptions()
          .position(new LatLng(latitude, longitude)));
     myOverlayItems.add(marker);
}

This says that if you have stored a latitude and longitude in your preferences, you want to draw the marker on your map at the given coordinates and add the marker to your overlay items list.

Answer 2

String fnail LOCATION_KEY = "key":
SharedPreferences preferences;

@Override
protected void onCreate(Bundle savedInstanceState) {

       preferences = getPreferences(MODE_APPEND);

       String location = preferences = getString(LOCATION_KEY ,"default Value");

}


@Override
protected void onPause() {
    // TODO Auto-generated method stub
    super.onPause();
    Editor editor = preferences.edit();
    editor.putString(LOCATION_KEY, "what ever you want");
    editor.commit();

}

this is in generally how to use SharedPreferences just do same thing in your project
i hope this helps