Question

我正在尝试保存并从Firebase检索位置并将其放入Google地图中。纬度和经度值在用户ID下，因为它将用于特定用户的位置。保存位置是成功的，但我无法检索它。我正在尝试检索它，但我一直在

java.lang.NullPointerException：尝试调用虚方法对空对象引用'double java.lang.Double.doubleValue（）' 错误。

有什么方法可以解决或做到这一点？提前谢谢。

以下是保存位置的代码：

    profDatabase = FirebaseDatabase.getInstance().getReference().child("Profile");

       if (auth.getCurrentUser() != null){

                    String userid = auth.getCurrentUser().getUid();
                    final DatabaseReference locDatabase = FirebaseDatabase.getInstance()
                            .getReferenceFromUrl("https://sholoco-9cf1e.firebaseio.com/Profile/" + userid);

                    profDatabase.child(userid).addValueEventListener(new ValueEventListener() {
                        @Override
                        public void onDataChange(DataSnapshot dataSnapshot) {
                            String stallname = dataSnapshot.child("StallName").getValue().toString();

                            Marker marker = mMap.addMarker(new
                                    MarkerOptions().position(point).title(stallname));
                            final LatLng latlng = marker.getPosition();

                            mSaveButton.setOnClickListener(new View.OnClickListener() {
                                @Override
                                public void onClick(View v) {
                                    //DatabaseReference newPost = profDatabase.push();
                                    //newPost.setValue(latlng);

                                    String latkey = "latitude";
                                    double latvalue = latlng.latitude;
                                    DatabaseReference child = locDatabase.child(latkey);
                                    child.setValue(latvalue);

                                    String longkey = "longitude";
                                    double longvalue = latlng.longitude;
                                    child = locDatabase.child(longkey);
                                    child.setValue(longvalue);
                                }
                            });
                        }

                        @Override
                        public void onCancelled(DatabaseError databaseError) {

                        }
                    });

这是我检索位置的代码：

profDatabase = FirebaseDatabase.getInstance().getReference().child("Profile");
        if (auth.getCurrentUser() != null) {

            String userid = auth.getCurrentUser().getUid();
            profDatabase.child(userid).addChildEventListener(new ChildEventListener() {
                @Override
                public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                    double latt = (double) dataSnapshot.child("latitude").getValue();
                    double longg = (double) dataSnapshot.child("longitude").getValue();
                    String stallname = dataSnapshot.child("StallName").getValue().toString();

                    LatLng newLocation = new LatLng(latt, longg);

                    mMap.addMarker(new MarkerOptions()
                            .position(newLocation)
                            .title(stallname));
                }

                @Override
                public void onChildChanged(DataSnapshot dataSnapshot, String s) {

                }

                @Override
                public void onChildRemoved(DataSnapshot dataSnapshot) {

                }

                @Override
                public void onChildMoved(DataSnapshot dataSnapshot, String s) {

                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            });
        }

我的数据库中的截图：

Answer 1

您是否尝试过使用addListenerForSingleValueEvent()代替addChildEventListener()？

获取没有userid的值：请参阅https://stackoverflow.com/a/46651960/4653447

 FirebaseDatabase.getInstance().getReference().child("Profile").addValueEventListener(new ValueEventListener() {
    public void onDataChange(DataSnapshot dataSnapshot) {
         for (DataSnapshot snapshot: dataSnapshot.getChildren()) {
            double latt = (double) snapshot.child("latitude").getValue();
            double longg = (double) snapshot.child("longitude").getValue();
           //store this data in list
         }
    }

Answer 2

您不需要将投射纬度和经度输入double，而是将Double.class作为参数传递给getValue()

            @Override
            public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                double latt = dataSnapshot.child("latitude").getValue(Double.class);
                double longg = dataSnapshot.child("longitude").getValue(Double.class);
                String stallname = dataSnapshot.child("StallName").getValue().toString();

                LatLng newLocation = new LatLng(latt, longg);

                mMap.addMarker(new MarkerOptions()
                        .position(newLocation)
                        .title(stallname));
            }

参考this answer

Answer 3

此代码有效

    @Override
public void onMapReady(GoogleMap googleMap) {
    mMap = googleMap;
    DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
    DatabaseReference locationsRef = rootRef.child("childName");
    final GeoFire geoFire = new GeoFire(locationsRef);
        geoFire.getLocation("dataKey", new LocationCallback() {
            @Override
            public void onLocationResult(String key, GeoLocation location) {
                double lat =location.latitude;
                double lng =location.longitude;
                LatLng sydney = new LatLng(lng, lat);
                mMap.addMarker(new MarkerOptions().icon(BitmapDescriptorFactory.defaultMarker(HUE_BLUE)).position(sydney).title("car"));
                Toast.makeText(getApplicationContext(),""+sydney,Toast.LENGTH_SHORT).show();
                mMap.moveCamera(CameraUpdateFactory.newLatLng(sydney));
                mMap.animateCamera(CameraUpdateFactory.zoomTo(9));
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
    

    if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
        return;
    }
    mMap = googleMap;
    mMap.setMyLocationEnabled(true);
    buildGoogleApiClient();

}

使用UID从Firebase检索位置并放入Google地图

3 个答案: