Question

我正在开发一个应用程序，该应用程序有一个名为 PostCar 的方法，调用该方法时应该创建一个数据库引用并将一个子项添加到我的 Firebase 控制台贷方表中，一个包含用户 ID 和位置的子项。问题是位置一直被标记为空。我的 PostCar 方法中的代码读取“geoFire.setLocation(userId,new GeoLocation(mlastlocation.getLatitude(),mlastlocation.getLongitude()));”不断抛出错误“尝试在空对象引用上调用虚拟方法‘double android.location.location.getlatitude()’”。设备位置已打开，我检查了位置权限。这是下面的代码。


package com.example.movir;

import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;
import androidx.core.content.ContextCompat;

import android.Manifest;
import android.app.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.pm.PackageManager;
import android.location.Location;
import android.location.LocationManager;
import android.os.Bundle;
import android.os.Looper;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

import com.firebase.geofire.GeoFire;
import com.firebase.geofire.GeoLocation;
import com.google.android.gms.location.FusedLocationProviderClient;
import com.google.android.gms.location.LocationCallback;
import com.google.android.gms.location.LocationRequest;
import com.google.android.gms.location.LocationResult;
import com.google.android.gms.location.LocationServices;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.tasks.OnSuccessListener;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;

public class LendersMenuPageActivity extends AppCompatActivity {

    private String userId;
    private FirebaseAuth mAuth;
    private LocationManager lm;
     Location mlastlocation;
    LocationRequest locationRequest;
    LocationCallback locationCallback;


    private Button lendcarButton;
    final LendCarForm cardlend = new LendCarForm(userId,"brand new Toyota","Toyota","Camry S9");
    private FusedLocationProviderClient fusedLocationClient;



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


        mAuth = FirebaseAuth.getInstance();
        fusedLocationClient = LocationServices.getFusedLocationProviderClient(this);
        fusedLocationClient.getLastLocation()
                .addOnSuccessListener(this, new OnSuccessListener<Location>() {
                    @Override
                    public void onSuccess(Location location) {
                        // Got last known location. In some rare situations this can be null.
                        if (location != null) {
                            // Logic to handle location object
                        }
                    }
                });



        FirebaseUser currentUser = mAuth.getCurrentUser();
        userId = currentUser.getUid();
        DatabaseReference lendersReference = FirebaseDatabase.getInstance().getReference("Users").child("Lenders").child(userId);
         lendcarButton = findViewById(R.id.lenders_car_button);
         lendcarButton.setOnClickListener(onClick);
        LocationManager lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE);

        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;
        }
        LocationCallback locationCallback = new LocationCallback() {
            @Override
            public void onLocationResult(LocationResult locationResult) {
                for (Location location : locationResult.getLocations()) {

                    if(getApplicationContext()!=null) {
                        mlastlocation = location;
                        LatLng latLng = new LatLng(location.getLatitude(), location.getLongitude());



                    }
                }
            }
        };
        mlastlocation = lm.getLastKnownLocation(LocationManager.GPS_PROVIDER);






    }

    @Override
    protected void onStart() {
        super.onStart();
        checkLocationPermission();
    }

    private void startLocationUpdates() {
        fusedLocationClient.requestLocationUpdates(locationRequest,
                locationCallback,
                Looper.getMainLooper());
    }
    public View.OnClickListener onClick = new View.OnClickListener() {
        @Override
        public void onClick(View v) {
         Toast.makeText(LendersMenuPageActivity.this,"hello",Toast.LENGTH_LONG);
            postCar();
        }
    };

private void checkLocationPermission() {
    if (ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
        if (ActivityCompat.shouldShowRequestPermissionRationale(this, Manifest.permission.ACCESS_FINE_LOCATION)) {
            new AlertDialog.Builder(this)
                    .setTitle("give permission")
                    .setMessage("give permission messaage")
                    .setPositiveButton("Ok", new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialog, int which) {
                            ActivityCompat.requestPermissions(LendersMenuPageActivity.this, new String[]{
                                    Manifest.permission.ACCESS_FINE_LOCATION
                            }, 1);
                        }
                    })
                    .create()
                    .show();

        } else {
            ActivityCompat.requestPermissions(LendersMenuPageActivity.this, new String[]{
                    Manifest.permission.ACCESS_FINE_LOCATION
            }, 1);
        }



    }
}

    public void postCar(){

       DatabaseReference carsForRent = FirebaseDatabase.getInstance().getReference("Users").child("Lenders").child(userId);

       GeoFire geoFire = new GeoFire(carsForRent);
     geoFire.setLocation(userId,new GeoLocation(mlastlocation.getLatitude(),mlastlocation.getLongitude()));

       carsForRent.setValue(cardlend);
    }
}

Answer 1

您是否正在使用 Xcode IOS 模拟器对此进行测试？模拟器实际上无法访问您的真实位置，因此在查询时它将返回 null，除非手动指定（功能选项卡、位置、自定义位置。）

Answer 2

fusedapi 对我不起作用的原因是因为我没有使用谷歌地图项目。所以我overode onlocatiochanged 代替。这对我有用，但你必须扩展 onlcationchanged 和 googleapi

我不断收到错误，位置为空

2 个答案: