java - 我在 Android Studio 的谷歌地图中得到零经度和纬度值

Question

这是我的 MapsActivity.java 代码，在 map 上放置标记并调用 getCurrentlocation() 后，我得到的经度和纬度值为零。出了什么问题？

public class MapsActivity extends FragmentActivity implements
        OnMapReadyCallback,
        GoogleApiClient.ConnectionCallbacks,
        GoogleApiClient.OnConnectionFailedListener,
        GoogleMap.OnMarkerDragListener,
        GoogleMap.OnMapLongClickListener,
        View.OnClickListener {

    //Our Map
    private GoogleMap mMap;

    //To store longitude and latitude from map
    private double longitude;
    private double latitude;

    //Buttons
    private ImageButton buttonSave;
    private ImageButton buttonCurrent;
    private ImageButton buttonView;

    //Google ApiClient
    private GoogleApiClient googleApiClient;


    @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);

        //Initializing googleapi client
        googleApiClient = new GoogleApiClient.Builder(this)
                .addConnectionCallbacks(this)
                .addOnConnectionFailedListener(this)
                .addApi(LocationServices.API)
                .build();

        //Initializing views and adding onclick listeners
        buttonSave = (ImageButton) findViewById(R.id.buttonSave);
        buttonCurrent = (ImageButton) findViewById(R.id.buttonCurrent);
        buttonView = (ImageButton) findViewById(R.id.buttonView);
        buttonSave.setOnClickListener(this);
        buttonCurrent.setOnClickListener(this);
        buttonView.setOnClickListener(this);
    }

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

    @Override
    protected void onStop() {
        googleApiClient.disconnect();
        super.onStop();
    }

    //Getting current location
    private void getCurrentLocation() {
        mMap.clear();
        //Creating a location object
        if (ActivityCompat.checkSelfPermission(this, android.Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, android.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;
        }
        if (ActivityCompat.checkSelfPermission(this, android.Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, android.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;
        }
        Location location = LocationServices.FusedLocationApi.getLastLocation(googleApiClient);
        if (location != null) {
            //Getting longitude and latitude
            longitude = location.getLongitude();
            latitude = location.getLatitude();

            //moving the map to location
            moveMap();
        }
    }

    //Function to move the map
    private void moveMap() {
        //String to display current latitude and longitude
        String msg = latitude + ", "+longitude;

        //Creating a LatLng Object to store Coordinates
        LatLng latLng = new LatLng(latitude, longitude);

        //Adding marker to map
        mMap.addMarker(new MarkerOptions()
                .position(latLng) //setting position
                .draggable(true) //Making the marker draggable
                .title("Current Location")); //Adding a title

        //Moving the camera
        mMap.moveCamera(CameraUpdateFactory.newLatLng(latLng));

        //Animating the camera
        mMap.animateCamera(CameraUpdateFactory.zoomTo(15));

        //Displaying current coordinates in toast
        Toast.makeText(this, msg, Toast.LENGTH_LONG).show();
    }

    @Override
    public void onMapReady(GoogleMap googleMap) {
        mMap = googleMap;
        LatLng latLng = new LatLng(-34, 151);
        mMap.addMarker(new MarkerOptions().position(latLng).draggable(true));
        mMap.moveCamera(CameraUpdateFactory.newLatLng(latLng));
        mMap.setOnMarkerDragListener(this);
        mMap.setOnMapLongClickListener(this);
    }

    @Override
    public void onConnected(Bundle bundle) {
        getCurrentLocation();
    }

    @Override
    public void onConnectionSuspended(int i) {

    }

    @Override
    public void onConnectionFailed(ConnectionResult connectionResult) {

    }

    @Override
    public void onMapLongClick(LatLng latLng) {
        //Clearing all the markers
        mMap.clear();

        //Adding a new marker to the current pressed position
        mMap.addMarker(new MarkerOptions()
                .position(latLng)
                .draggable(true));
        String msg = latitude + ", "+longitude;
        Toast.makeText(this, msg, Toast.LENGTH_LONG).show();


    }

    @Override
    public void onMarkerDragStart(Marker marker) {

    }

    @Override
    public void onMarkerDrag(Marker marker) {

    }

    @Override
    public void onMarkerDragEnd(Marker marker) {
        //Getting the coordinates
        latitude = marker.getPosition().latitude;
        longitude = marker.getPosition().longitude;

        //Moving the map
        moveMap();
    }

    @Override
    public void onClick(View v) {
        if(v == buttonCurrent){
            getCurrentLocation();
            moveMap();
        }
    }
}

Answer 1

GetLastLocation 仅返回可用位置。 99%的时间都不会。使用 requestLocationUpdates 或 requestSingleUpdate 确保获取位置(请注意，这两个函数都是异步函数，因为获取位置需要时间)。