如何从firebase数据库添加谷歌地图标记

Question

我想从 firebase 数据库中检索位置标记，但在运行此代码后我看不到任何标记。我试图制作EventListener，但地图运行时没有任何标记。这是我的代码：

public class MapsActivity extends FragmentActivity implements OnMapReadyCallback {

    private GoogleMap mMap;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_maps);
        // Obtain the SupportMapFragment and get notified when the map is ready to be used.
        SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
                .findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);

    }


    /**
     * Manipulates the map once available.
     * This callback is triggered when the map is ready to be used.
     * This is where we can add markers or lines, add listeners or move the camera. In this case,
     * we just add a marker near Sydney, Australia.
     * If Google Play services is not installed on the device, the user will be prompted to install
     * it inside the SupportMapFragment. This method will only be triggered once the user has
     * installed Google Play services and returned to the app.
     */
    @Override
    public void onMapReady(GoogleMap googleMap) {
        mMap = googleMap;
        DatabaseReference ref = FirebaseDatabase.getInstance().getReference();




                    String rightLocation = ref.child("location_right").toString();
                    String leftLocation = ref.child("location_left").toString();

                    double location_left = Double.valueOf(leftLocation);
                    double location_right = Double.valueOf(rightLocation);
                    LatLng sydney = new LatLng(location_left, location_right);
                    mMap.addMarker(new MarkerOptions().position(sydney).title("Marker in Sydney"));
                    mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(sydney,18));











        // Add a marker in Sydney and move the camera

    }
}

这里可能有什么问题？

Answer 1

您需要使用ValueEventListener 从 Firebase 数据库获取数据。这在the documentation 中有解释。

@Override
public void onMapReady(GoogleMap googleMap) {
    mMap = googleMap;
    DatabaseReference ref = FirebaseDatabase.getInstance().getReference();

    ref.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            if (dataSnapshot.exists()) {
                double location_left = dataSnapshot.child("location_left").getValue(Double.class);
                double location_right = dataSnapshot.child("location_right").getValue(Double.class);
                LatLng sydney = new LatLng(location_left, location_right);
                mMap.addMarker(new MarkerOptions().position(sydney).title("Marker in Sydney"));
                mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(sydney,18));
            } else {
                Log.e(TAG, "onDataChange: No data");
            }

        }
        @Override
        public void onCancelled(DatabaseError databaseError) {
            throw databaseError.toException();
        }
    });