试图将我的地图集中在用户位置上（说位置为空）

Question

我一直试图将地图放在用户位置的中心，但它一直说 latLng 变量为空。我已经读到发生这种情况是因为我正在使用 getLastKnownLocation，但我找不到任何其他方法来做到这一点（我是编程新手）。我正在使用 Jellybean 上的 google api。这是我正在使用的代码。

if (ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION)
                == PackageManager.PERMISSION_GRANTED) {
            mMap.setMyLocationEnabled(true);

 LocationManager locationManager = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
      Criteria criteria = new Criteria();
        String provider = locationManager.getBestProvider(criteria,true);
        Location myLocation = locationManager.getLastKnownLocation(provider);

        //Latitude y longitud
        double latitude = myLocation.getLatitude();
        double longitude = myLocation.getLongitude();
        LatLng latLng = new LatLng(latitude,longitude);
        //Mover el mapa a la posicion actual del usuario
        mMap.moveCamera(CameraUpdateFactory.newLatLng(latLng));
        //Zoom
        mMap.animateCamera(CameraUpdateFactory.zoomTo(12));
        mMap.addMarker(new MarkerOptions().position(new LatLng(latitude, longitude)).title("You are here!").snippet("Consider yourself located"));






      } else {
            // Show rationale and request permission.
        }

Answer 1

试试这个

protected synchronized void buildGoogleApiClient() {
        mGoogleApiClient = new GoogleApiClient.Builder(this)
                .addConnectionCallbacks(this)
                .addOnConnectionFailedListener(this)
                .addApi(LocationServices.API)
                .build();
        mGoogleApiClient.connect();
    }

  //Initialize Google Play Services
        if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            if (bPermissionGranted) {
                buildGoogleApiClient();
                if (checkSelfPermission(Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && checkSelfPermission(Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
                    // TODO: Consider calling
                    //    public void requestPermissions(@NonNull String[] permissions, int requestCode)
                    // 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 Activity#requestPermissions for more details.
                    return;
                }
                mGoogleMap.setMyLocationEnabled(true);
            }
        } else {
            buildGoogleApiClient();
            mGoogleMap.setMyLocationEnabled(true);
        }

实现接口GoogleApiClient.ConnectionCallbacks并覆盖方法 onConnected 和 onConnectionSuspended 在 onConnected 中

 mLocationRequest = new LocationRequest();
        mLocationRequest.setInterval(1000);
        mLocationRequest.setFastestInterval(1000);
        mLocationRequest.setPriority(LocationRequest.PRIORITY_BALANCED_POWER_ACCURACY);
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            if (checkSelfPermission(Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && checkSelfPermission(Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
                // TODO: Consider calling
                //    public void requestPermissions(@NonNull String[] permissions, int requestCode)
                // 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 Activity#requestPermissions for more details.
                return;
            }
        }
        LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient, mLocationRequest, this);

在其中实现LocationListener接口和覆盖方法

@Override
public void onLocationChanged(Location location) {
    mLastLocation = location;
    if (mCurrLocationMarker != null) {
        mCurrLocationMarker.remove();
    }

    //Place current location marker
    LatLng latLng = new LatLng(location.getLatitude(), location.getLongitude());
    MarkerOptions markerOptions = new MarkerOptions();
    markerOptions.position(latLng);
    markerOptions.title("Current Position");
    markerOptions.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_MAGENTA));
    mCurrLocationMarker = mGoogleMap.addMarker(markerOptions);

    //move map camera
    mGoogleMap.moveCamera(CameraUpdateFactory.newLatLng(latLng));
    mGoogleMap.animateCamera(CameraUpdateFactory.zoomTo(11));

    if (mGoogleApiClient != null) {
        LocationServices.FusedLocationApi.removeLocationUpdates(mGoogleApiClient, this);
    }
}

Answer 2

检查“AndroidManifest.xml”中的权限

<user-permission android:name="android.permission.ACCESS_FINE_LOCATION />
<user-permission android:name="android.permission.ACCESS_COARSE_LOCATION />
<user-permission android:name="android.permission.INTERNET />

主要我们可以通过 GPS Provider 和 NETWORK Provider 获取位置。 如果我们通过 GPS 提供商获得空位置，则将 Provider 更改为 NETWORK。

LocationManager locationManager = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
String provideGps = locationManager.GPS_PROVIDER;
String provideNetwork = locationManager.NETWORK_PROVIDER;

Location location = locationManager.getLastKnownLocation(providerGps);

If (location == null) {
    location = locationManager.getLastKnownLocation(providerNetwork);
    location.getLatitude();
    location.getLongitude();
} else {
    location.getLatitude();
    location.getLongitude();
}