android–如何从firebase数据库添加谷歌地图标记

我想从firebase数据库中检索位置标记,但是在运行此代码后我看不到任何标记.我尝试制作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
}
}


这可能有什么问题？

解决方法:

您需要使用ValueEventListener从Firebase数据库获取数据.这在the documentation中解释.

@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();
}
});