Q:

Get back to my app after marker click on google maps

I had a problem in my app development. After a button click i can open Google Maps with current position of the user.
location_selection.setOnClickListener(new View.OnClickListener() {

            public void onClick(View v) {

                Location gpsLocation = appLocationService.getLocation(LocationManager.GPS_PROVIDER);
                Location nwLocation = appLocationService.getLocation(LocationManager.NETWORK_PROVIDER);

                if (gpsLocation != null) {

                    latitude = gpsLocation.getLatitude();
                    longitude = gpsLocation.getLongitude();

                } else if(nwLocation != null) {

                    latitude = nwLocation.getLatitude();
                    longitude = nwLocation.getLongitude();

                } else {

                    Toast hint = Toast.makeText(getApplicationContext(), "Please turn on GPS/Network", Toast.LENGTH_SHORT);
                    hint.show();

                }

                if(latitude != 0 && longitude != 0) {

                    Intent intent = new Intent(android.content.Intent.ACTION_VIEW, 
                            Uri.parse("geo:0,0?q="+latitude+","+longitude));
                    startActivity(intent);

                }

            }

        });

What i want to do is to retrieve coordinates and address of the marker that the user set after google maps has been open, and get back with this data to my app closing google map. But I really don't know how to do that!

A:

To obtain address from latitude and longitude of your current location
Take a look at this link 
https://developers.google.com/maps/documentation/geocoding/
Look for "Reverse Geocoding (Address Lookup)" might help
You will have to make http call to the google Geocoding API with your lat and long which retrieve JSON that contains addresses you interested about the location.  Sort your JSON in java into readable text. 
What i want to do is to retrieve coordinates
I am not sure what you meant in here,  since lat and long are already in the your code above
Hope it helps    

