基于数据库经纬度在Google Map添加Marker不显示问题求助

我需要用从数据库获取的纬度（latitude）和经度（longitude）在Google Map上添加标记，但标记始终不显示。已经确认能正常获取位置数据，求帮忙排查代码问题。

我的Java代码 #

public class PassengerMainscreen_Activity extends AppCompatActivity implements OnMapReadyCallback {

    boolean isPermissionGranted;
    TextView textView;
    DatabaseReference firebaseDatabase;
    GoogleMap googleMap;
    Marker marker;


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

        checkpermission();
        textView = findViewById(R.id.LocEmpty);

        //CHECKING GOOGLE PLAY SERVICES
        if (isPermissionGranted) {
            if (checkGooglePlayServices()) {
                SupportMapFragment supportMapFragment = SupportMapFragment.newInstance();
                getSupportFragmentManager().beginTransaction().add(R.id.CONTAINER, supportMapFragment).commit();
                supportMapFragment.getMapAsync(this);
            } else {
                Toast.makeText(this, "Google Play Services Not available", Toast.LENGTH_SHORT).show();
            }
        }
    }

    private boolean checkGooglePlayServices() {
        GoogleApiAvailability googleApiAvailability = GoogleApiAvailability.getInstance();
        int result = googleApiAvailability.isGooglePlayServicesAvailable(this);
        if (result == ConnectionResult.SUCCESS) {
            return true;
        } else if (googleApiAvailability.isUserResolvableError(result)) {
            Dialog dialog = googleApiAvailability.getErrorDialog(this, result, 201, new DialogInterface.OnCancelListener() {
                @Override
                public void onCancel(DialogInterface dialog) {
                    Toast.makeText(PassengerMainscreen_Activity.this, "User Cancelled Dialog", Toast.LENGTH_SHORT).show();
                }
            });
            dialog.show();
        }
        return false;
    }

    private void checkpermission() {
        Dexter.withContext(this).withPermission(Manifest.permission.ACCESS_FINE_LOCATION).withListener(new PermissionListener() {
            @Override
            public void onPermissionGranted(PermissionGrantedResponse permissionGrantedResponse) {
                isPermissionGranted = true;
                Toast.makeText(PassengerMainscreen_Activity.this, "Permission Granted", Toast.LENGTH_SHORT).show();
            }

            @Override
            public void onPermissionDenied(PermissionDeniedResponse permissionDeniedResponse) {
                Intent intent = new Intent();
                intent.setAction(Settings.ACTION_APPLICATION_DETAILS_SETTINGS);
                Uri uri = Uri.fromParts("package", getPackageName(), "");
                intent.setData(uri);
                startActivity(intent);
            }

            @Override
            public void onPermissionRationaleShouldBeShown(PermissionRequest permissionRequest, PermissionToken permissionToken) {
                permissionToken.continuePermissionRequest();
            }
        }).check(); //PERMISSION END
    }

    @Override
    public void onMapReady(@NonNull GoogleMap googleMap) {
        this.googleMap = googleMap;


        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
            // TODO: Consider calling
            //    ActivityCompat#requestPermissions
            // here to request the missing permissions, and then overriding
            //   public void onRequestPermissionsResult(int requestCode, String[] permissions,
            //                                          int[] grantResults)
            // to handle the case where the user grants the permission. See the documentation
            // for ActivityCompat#requestPermissions for more details.
            return;
        }
        googleMap.setMyLocationEnabled(true);

      getbusLocation();
      
    }

    private void getbusLocation() {

        firebaseDatabase = FirebaseDatabase.getInstance().getReference().child("Location");
        firebaseDatabase.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {

                Double lat = Double.valueOf(snapshot.child("latitude").getValue().toString());
                Double lng = Double.valueOf(snapshot.child("longitude").getValue().toString());
                textView.setText(lat + "," + lng);

                // DISPLAYING MARKER ON THE MAP
                LatLng loc = new LatLng(lat, lng);
                MarkerOptions markerOptions = new MarkerOptions();
                markerOptions.position(loc);
                marker = googleMap.addMarker(markerOptions);
            }

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

            }
        });
    }

}

排查关键点 #

• 权限与地图初始化时机错误：checkpermission是异步操作，onCreate中直接判断isPermissionGranted时，权限还没申请完成，导致地图Fragment未被添加，onMapReady不会触发。需将地图初始化逻辑移到onPermissionGranted回调内：

  @Override
  public void onPermissionGranted(PermissionGrantedResponse permissionGrantedResponse) {
      isPermissionGranted = true;
      Toast.makeText(PassengerMainscreen_Activity.this, "Permission Granted", Toast.LENGTH_SHORT).show();
      // 权限通过后再初始化地图
      if (checkGooglePlayServices()) {
          SupportMapFragment supportMapFragment = SupportMapFragment.newInstance();
          getSupportFragmentManager().beginTransaction().add(R.id.CONTAINER, supportMapFragment).commit();
          supportMapFragment.getMapAsync(PassengerMainscreen_Activity.this);
      } else {
          Toast.makeText(PassengerMainscreen_Activity.this, "Google Play Services Not available", Toast.LENGTH_SHORT).show();
      }
  }
  

• 地图容器布局问题：检查布局文件中R.id.CONTAINER是否为有效容器（如FrameLayout），且尺寸设置为match_parent，避免地图无显示空间。
• 未调整地图视角到标记位置：添加标记后，地图可能停留在默认位置，导致标记不在视野内。添加标记后调用：

  googleMap.moveCamera(CameraUpdateFactory.newLatLngZoom(loc, 15f));
  

• 数据转换存在空指针风险：直接转换数据库值可能因字段为空或格式错误抛出异常，需先判断非空：

  Object latObj = snapshot.child("latitude").getValue();
  Object lngObj = snapshot.child("longitude").getValue();
  if (latObj != null && lngObj != null) {
      Double lat = Double.parseDouble(latObj.toString());
      Double lng = Double.parseDouble(lngObj.toString());
      // 后续标记逻辑
  }
  

• 重复添加标记优化：数据库更新时会重复添加标记，建议先移除旧标记：

  if (marker != null) {
      marker.remove();
  }
  marker = googleMap.addMarker(markerOptions);
  

内容的提问来源于stack exchange，提问作者prince