CODEWITHSUNDEEP
javaandroidfirebase-realtime-database
SyfJO
SyfJO

Reputation: 5

App crashes because of null object reference

I have a problem when calling (user.getlat) and (user.getlng). I have declared user object globally, and initialized it in the getUserData() method.

but when I run the app the app crashes and in the logcat is says:

java.lang.NullPointerException: Attempt to invoke virtual method 'double com.example.profile.User.getLat()' on a null object reference

public class Profile extends FragmentActivity implements OnMapReadyCallback {

private GoogleMap mMap;
private LocationManager locationManager;
private LocationListener locationListener;

private FirebaseAuth mAuth;
DatabaseReference database = FirebaseDatabase.getInstance().getReference();
DatabaseReference myRef = database.child("users");
User user;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_profile);

    SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
            .findFragmentById(R.id.mapFragment);
    mapFragment.getMapAsync(this);

    mAuth = FirebaseAuth.getInstance();
}

public void getUserData(){
    String uID = mAuth.getCurrentUser().getUid();
    myRef.child(uID).addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {

            dataSnapshot.getChildren();
            user = dataSnapshot.getValue(User.class);

            Toast.makeText(Profile.this, "" + user.lng, Toast.LENGTH_LONG).show(); // Prints the value normally!

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            Toast.makeText(Profile.this, "Failed to read from database!", Toast.LENGTH_LONG).show();
        }
    });
}

@Override
public void onMapReady(GoogleMap googleMap) {
    mMap = googleMap;

    LatLng userL = new LatLng(user.getLat(),user.getLng()); // The problem occurs here! 
    mMap.clear();
    mMap.addMarker(new MarkerOptions().position(userL).title("Your Location"));
    mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(userL,17));

}

}

Upvotes: 0

Views: 109

Answers (1)

uneq95
uneq95

Reputation: 2228

First of all, you haven't called getUserData() method in anywhere. I read that you tried to add that logic in onCreate() too, but it didn't work.

Adding a listener doesn't mean that you will get what is expected of it, instantaneously.

Use the onMapReady() method only to set the map, with settings which is not dependent on User. Add/Modify the map marker only when you detect changes in the User data. See the changes:

public void getUserData(){
    String uID = mAuth.getCurrentUser().getUid();
    myRef.child(uID).addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {

            dataSnapshot.getChildren();
            user = dataSnapshot.getValue(User.class);
            LatLng userL = new LatLng(user.getLat(),user.getLng());
            if(mMap!=null){
               mMap.clear();
               mMap.addMarker(new MarkerOptions().position(userL).title("Your 
               Location"));
             mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(userL,17));
            }
            Toast.makeText(Profile.this, "" + user.lng, Toast.LENGTH_LONG).show(); // Prints the value normally!

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            Toast.makeText(Profile.this, "Failed to read from database!", Toast.LENGTH_LONG).show();
        }
    });
}

@Override
public void onMapReady(GoogleMap googleMap) {
    mMap = googleMap;
}

Please call the method getUserData() or move its code in onCreate().

Upvotes: 1

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