Maps API only loads with location setting GPS

问题

I use the Google Maps API in my Android app and locate the user with LocationManager and getLongitude(), getLatitude(). But now there have to be strange settings on the mobile phone to get a map. The location setting has to be changed to only use GPS, and even then it's not working all the time, sometimes the map is not loaded. If not loaded the app shuts down at the point the first marker is set because of NullPointerException.

Why is this and how can I prevent it? I already tried with getMapAsync but it didn't help.

GoogleMap googleMap;
LocationManager locationManager;
String provider;
Criteria criteria;
Location myLocation;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_map);

   try {
        if(googleMap == null) {
            googleMap = ((MapFragment) getFragmentManager().findFragmentById(R.id.map)).getMap();
        }
        googleMap.setMapType(GoogleMap.MAP_TYPE_HYBRID);
        googleMap.setMyLocationEnabled(true);
        googleMap.setTrafficEnabled(true);
        googleMap.setIndoorEnabled(true);
        googleMap.setBuildingsEnabled(true);
        googleMap.getUiSettings().setZoomControlsEnabled(true);

        locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
        criteria = new Criteria();
        provider = locationManager.getBestProvider(criteria, true);
        myLocation = locationManager.getLastKnownLocation(provider);
        double latitude = myLocation.getLatitude();
        double longitude = myLocation.getLongitude();
        LatLng latLng = new LatLng(latitude, longitude);
        googleMap.moveCamera(CameraUpdateFactory.newLatLng(latLng));
        googleMap.animateCamera(CameraUpdateFactory.zoomTo(14));
        iconDone = R.drawable.markerdone;
        icon = R.drawable.marker;
    }
    catch(Exception e) {
        e.printStackTrace();
    }

    Marker marker1 = googleMap.addMarker(new MarkerOptions()
            .position(new LatLng(49.793012, 9.926201))
            .title(getString(R.string.Title1))
            .snippet("")
            .icon(BitmapDescriptorFactory.fromResource(icon)));

回答1:

The problem is that you're calling getLastKnownLocation(), which will frequently return a null Location, since it doesn't explicitly request a new location lock.

So, when your app is crashing, it's due to a NullPointerException when trying to de-reference the Location object.

It's best to request location updates, and if you only need one, just un-register for location updates once the first onLocationChanged() callback comes in.

Here is an example using the FusedLocationProvider API, which automatically uses Network Location as well as GPS Location if needed:

Relevant imports for the Activity:

import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.api.GoogleApiClient;
import com.google.android.gms.location.LocationListener;
import com.google.android.gms.location.LocationRequest;
import com.google.android.gms.location.LocationServices;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.OnMapReadyCallback;
import com.google.android.gms.maps.model.BitmapDescriptorFactory;
import com.google.android.gms.maps.model.CameraPosition;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.Marker;
import com.google.android.gms.maps.model.MarkerOptions;

Activity:

public class MainActivity extends AppCompatActivity 
        implements OnMapReadyCallback,
        GoogleApiClient.ConnectionCallbacks, 
        GoogleApiClient.OnConnectionFailedListener, LocationListener {


    GoogleMap googleMap;
    LocationRequest mLocationRequest;
    GoogleApiClient mGoogleApiClient;
    Marker marker;

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

        buildGoogleApiClient();
        mGoogleApiClient.connect();
    }

    @Override
    protected void onResume() {
        super.onResume();

        SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
                .findFragmentById(R.id.map);

        mapFragment.getMapAsync(this);
    }

    protected synchronized void buildGoogleApiClient() {
        Toast.makeText(this,"buildGoogleApiClient", Toast.LENGTH_SHORT).show();
        mGoogleApiClient = new GoogleApiClient.Builder(this)
                .addConnectionCallbacks(this)
                .addOnConnectionFailedListener(this)
                .addApi(LocationServices.API)
                .build();
    }

    @Override
    public void onMapReady(GoogleMap map) {

        googleMap = map;

        setUpMap();

    }

    public void setUpMap() {

        googleMap.setMapType(GoogleMap.MAP_TYPE_HYBRID);
        googleMap.setMyLocationEnabled(true);
        googleMap.getUiSettings().setZoomControlsEnabled(true);

    }

    @Override
    public void onConnected(Bundle bundle) {

        mLocationRequest = new LocationRequest();
        mLocationRequest.setInterval(10);
        mLocationRequest.setFastestInterval(10);
        mLocationRequest.setPriority(LocationRequest.PRIORITY_BALANCED_POWER_ACCURACY);
        //mLocationRequest.setSmallestDisplacement(0.1F);

        LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient, mLocationRequest, this);
    }

    @Override
    public void onConnectionSuspended(int i) {

    }

    @Override
    public void onLocationChanged(Location location) {

        //unregister location updates
        LocationServices.FusedLocationApi.removeLocationUpdates(mGoogleApiClient, this);

        //remove previously placed Marker
        if (marker != null) {
            marker.remove();
        }

        LatLng latLng = new LatLng(location.getLatitude(), location.getLongitude());
        //place marker where user just clicked
        marker = googleMap.addMarker(new MarkerOptions()
                .position(latLng)
                .title("Current Location")
                .icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_MAGENTA)));

        CameraPosition cameraPosition = new CameraPosition.Builder()
                .target(latLng).zoom(5).build();

        googleMap.animateCamera(CameraUpdateFactory
                .newCameraPosition(cameraPosition));


    }

    @Override
    public void onConnectionFailed(ConnectionResult connectionResult) {

    }

}

build.gradle (change to whatever version of Google Play Services you are currently using):

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    compile 'com.android.support:appcompat-v7:22.1.1'
    compile 'com.google.android.gms:play-services:7.5.0'
}

SupportMapFragment in the layout xml (you can use a MapFragment as well):

    <fragment
    android:id="@+id/map"
    class="com.google.android.gms.maps.SupportMapFragment"
    android:layout_width="match_parent"
    android:layout_height="match_parent"/>

Using only Network Location:

The Map moves to the current location seconds after launch:

来源：https://stackoverflow.com/questions/31448001/maps-api-only-loads-with-location-setting-gps