我的应用不显示Google地图

Question

我正在使用谷歌地图开发一个Android应用程序，我编辑了代码以获取当前用户位置，但是当我运行代码时，地图不会出现。我没有收到任何错误或警告。我在模拟器上看到的只有灰色屏幕，上面有一个标记 请让我知道我做错了什么。

package com.example.shubham.mapsandgeolcationservices;
import android.Manifest;
import android.content.Context;
import android.content.pm.PackageManager;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Build;
import android.support.annotation.NonNull;
import android.support.v4.app.ActivityCompat;
import android.support.v4.app.FragmentActivity;
import android.os.Bundle;
import android.support.v4.content.ContextCompat;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.OnMapReadyCallback;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;

import static android.location.LocationManager.*;

public class MapsActivity extends FragmentActivity implements OnMapReadyCallback {
    LocationManager locationManager;
    LocationListener locationListener;
    private GoogleMap mMap;

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
            if (ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) == PackageManager.PERMISSION_GRANTED)
                locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locationListener);
        }

        }





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



    /**
     * Manipulates the map once available.
     * This callback is triggered when the map is ready to be used.
     * This is where we can add markers or lines, add listeners or move the camera. In this case,
     * we just add a marker near Sydney, Australia.
     * If Google Play services is not installed on the device, the user will be prompted to install
     * it inside the SupportMapFragment. This method will only be triggered once the user has
     * installed Google Play services and returned to the app.
     */
    @Override
    public void onMapReady(GoogleMap googleMap) {
        mMap = googleMap;

        locationManager = (LocationManager)this.getSystemService(Context.LOCATION_SERVICE);
        locationListener = new LocationListener() {
            @Override
            public void onLocationChanged(Location location) {
                // Add a marker in Sydney and move the camera
                LatLng ShanivarWada= new LatLng(location.getLatitude(),location.getLongitude());
                mMap.clear();
                mMap.setMapType(GoogleMap.MAP_TYPE_NORMAL);
                mMap.addMarker(new MarkerOptions().position(ShanivarWada).title("Shaniwar Wada"));
                mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(ShanivarWada,18));
            }

            @Override
            public void onStatusChanged(String provider, int status, Bundle extras) {

            }

            @Override
            public void onProviderEnabled(String provider) {

            }

            @Override
            public void onProviderDisabled(String provider) {

            }
        };

        if(Build.VERSION.SDK_INT<23){
            locationManager.requestLocationUpdates(GPS_PROVIDER,0,0,locationListener);
        }
        else {
            if(ContextCompat.checkSelfPermission(this,Manifest.permission.ACCESS_FINE_LOCATION)!=PackageManager.PERMISSION_GRANTED)
            {
                ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, 1);
            }else{
               locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locationListener);

                Location lastKnownLocation = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);

                LatLng ShanivarWada= new LatLng(lastKnownLocation.getLatitude(),lastKnownLocation.getLongitude());
                mMap.clear();
                mMap.setMapType(GoogleMap.MAP_TYPE_NORMAL);
                mMap.addMarker(new MarkerOptions().position(ShanivarWada).title("Shaniwar Wada"));
                mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(ShanivarWada,18));
            }
        }

    }
}