从 Firebase 检索位置数据未进入 MapActivity

Question

所以，我想从我的数据库参考路径“驱动程序位置”中获取latitude 和longitude。但是，它什么也没发生，只是显示正常的谷歌地图而不触发位置。请帮忙！

public class StudentMapActivity extends FragmentActivity implements OnMapReadyCallback {

    private GoogleMap mMap;
    private DatabaseReference databaseReference;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_student_map);
        FirebaseDatabase database = FirebaseDatabase.getInstance();
        databaseReference = database.getReference("Driver Location");

        // 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(final GoogleMap googleMap) {
        mMap = googleMap;
        databaseReference.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {

                for (DataSnapshot child : dataSnapshot.getChildren()) {
                    String lat = child.child("latitude").getValue().toString();
                    String lng = child.child("longitude").getValue().toString();

                    double latitude = Double.parseDouble(lat);
                    double longitude = Double.parseDouble(lng);
                    LatLng latLng = new LatLng(latitude, longitude);
                    MarkerOptions markerOptions = new MarkerOptions()
                            .position(latLng)
                            .title("Bus is here");
                    mMap.addMarker(markerOptions);
                    mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(latLng, 16));
                }
            }

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

            }
        });


    }

}

Logcat：

2020-07-24 00:41:18.926 22586-22586/com.example.upmbus D/InputTransport: Input channel destroyed: '1df605 ', fd=100
2020-07-24 00:41:18.939 22586-23234/com.example.upmbus W/.example.upmbu: Accessing hidden method Lsun/misc/Unsafe;->getLong(Ljava/lang/Object;J)J (greylist,core-platform-api, linking, allowed)
2020-07-24 00:41:18.940 22586-23234/com.example.upmbus W/.example.upmbu: Accessing hidden method Lsun/misc/Unsafe;->putLong(Ljava/lang/Object;JJ)V (greylist, linking, allowed)
2020-07-24 00:41:18.942 22586-23234/com.example.upmbus W/.example.upmbu: Accessing hidden method Lsun/misc/Unsafe;->getObject(Ljava/lang/Object;J)Ljava/lang/Object; (greylist, linking, allowed)
2020-07-24 00:41:18.942 22586-23234/com.example.upmbus W/.example.upmbu: Accessing hidden method Lsun/misc/Unsafe;->getInt(Ljava/lang/Object;J)I (greylist, linking, allowed)

附加的数据库详细信息

Answer 1

没有必要循环遍历DataSnapshot 对象，因为那里只有两个属性，并且都可以像下面的代码行一样直接访问：

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference driverLocationRef = rootRef.child("Driver Location");
ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        double latitude = dataSnapshot.child("latitude").getValue(Double.class);
        double longitude = dataSnapshot.child("longitude").getValue(Double.class);
        Log.d("TAG", latitude + ", " + longitude);
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        Log.d("TAG", databaseError.getMessage()); //Don't ignore errors!
    }
};
driverLocationRef.addListenerForSingleValueEvent(valueEventListener);

logcat 中的结果将是：

3.0227801, 101.71208

除此之外，使用：

String lng = child.child("longitude").getValue().toString();

没有任何意义，因为这两个属性都持有一个双精度值，而不是一个字符串。