如何获取Firebase实时数据库中保存的所有地址，并将其显示为google地图上的标记

Question

我需要确保用户添加的标记对google maps活动中的所有其他用户也是可见的，因此，例如，如果4个用户在地图的末尾各放置一个标记，则必须显示所有4个。我试着这样做，但一旦我点击Cardview，就可以进入谷歌地图。

我在addrees之前使用了日志，也使用了gender，它们都是“Null”，我如何解决？

出现此错误

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference
    at com.example.chatapp.Fragments.TrovamicoActivity$1.lambda$onDataChange$1$com-example-chatapp-Fragments-TrovamicoActivity$1(TrovamicoActivity.java:88)
    at com.example.chatapp.Fragments.TrovamicoActivity$1$$ExternalSyntheticLambda1.onComplete(Unknown Source:2)
    at com.google.android.gms.tasks.zzi.run(com.google.android.gms:play-services-tasks@@18.0.1:1)
    at android.os.Handler.handleCallback(Handler.java:938)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:223)
    at android.app.ActivityThread.main(ActivityThread.java:7656)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)

GoogleMaps活动

 public static final String TAG = "addreess";

//private GoogleMap mMap;
private FragmentsTrovamicoBinding binding;
LatLng latLng;


private DatabaseReference reference;
private FirebaseUser firebaseUser;

List<String> addresses, genders;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    binding = FragmentsTrovamicoBinding.inflate(getLayoutInflater());
    setContentView(binding.getRoot());
    Log.d(TAG, "String addreess: " + addresses);
    addresses = new ArrayList<>();
    genders = new ArrayList<>();

    firebaseUser = FirebaseAuth.getInstance().getCurrentUser();
    reference = FirebaseDatabase.getInstance().getReference("Users").child(firebaseUser.getUid());

  

    ValueEventListener eventListener = new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot snapshot) {
            for (DataSnapshot dataSnapshot: snapshot.getChildren()) {
                reference.child("address").get().addOnCompleteListener(task -> {
                    if (task.isSuccessful()) {
                        String address = task.getResult().getValue().toString();
                        addresses.add(address);
                    }
                });
                Log.d(TAG, "String addreess: " + addresses);
                reference.child("gender").get().addOnCompleteListener(task -> {
                    if (task.isSuccessful()) {
                        String gender = task.getResult().getValue().toString();
                        genders.add(gender);
                    }
                });
            }
        }

        @Override
        public void onCancelled(@NonNull DatabaseError error) {

        }
    };

    reference.addListenerForSingleValueEvent(eventListener);

    // 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);
}

@Override
public void onMapReady(GoogleMap googleMap) {

    for (int i = 0; i < addresses.size(); i++) {
        String user_address = addresses.get(i);
        if (!user_address.equals("To be added")) {
            Log.d(TAG, "String addreess: " + addresses);
            String user_gender = genders.get(i);
            latLng = getLocationFromAddress(user_address);
            MarkerOptions markerOptions = new MarkerOptions();
            markerOptions.position(latLng);
            markerOptions.title("You");
            Log.d(TAG, "String addreess: " + addresses);
            markerOptions.icon(BitmapFromVector(getApplicationContext(), (user_gender.equals("Male")) ? R.drawable.male : R.drawable.female));
            googleMap.clear();
            googleMap.animateCamera(CameraUpdateFactory.newLatLngZoom(latLng, 5));
            googleMap.addMarker(markerOptions);
        }
    }
}

public LatLng getLocationFromAddress(String strAddress) {

    Geocoder coder = new Geocoder(this);
    List<Address> address;
    LatLng p1;

    try {
        address = coder.getFromLocationName(strAddress, 5);
        if (address == null) {
            return null;
        }
        Address location = address.get(0);
        p1 = new LatLng(location.getLatitude(), location.getLongitude());

        return p1;
    } catch (IOException e) {
        e.printStackTrace();
    }
    return null;
}

private BitmapDescriptor BitmapFromVector(Context context, int vectorResId) {
    // below line is use to generate a drawable.
    Drawable vectorDrawable = ContextCompat.getDrawable(context, vectorResId);

    // below line is use to set bounds to our vector drawable.
    vectorDrawable.setBounds(0, 0, vectorDrawable.getIntrinsicWidth(), vectorDrawable.getIntrinsicHeight());

    // below line is use to create a bitmap for our
    // drawable which we have added.
    Bitmap bitmap = Bitmap.createBitmap(vectorDrawable.getIntrinsicWidth(), vectorDrawable.getIntrinsicHeight(), Bitmap.Config.ARGB_8888);

    // below line is use to add bitmap in our canvas.
    Canvas canvas = new Canvas(bitmap);

    // below line is use to draw our
    // vector drawable in canvas.
    vectorDrawable.draw(canvas);

    // after generating our bitmap we are returning our bitmap.
    return BitmapDescriptorFactory.fromBitmap(bitmap);
}
}