地图应用程序打开时崩溃

Question

public class MainActivity extends FragmentActivity implements OnMapReadyCallback {

GoogleMap googleMap;

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

    SupportMapFragment supportMapFragment = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.frg_map);
    googleMap = supportMapFragment.getMap();
    googleMap.setMyLocationEnabled(true);

    supportMapFragment.getMapAsync(this);
}

public void onMapReady(GoogleMap googleMap) {
    googleMap.setMyLocationEnabled(true);

    Criteria criteria = new Criteria();
    LocationManager locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);
    String mMapProvider = locationManager.getBestProvider(criteria, true);

    if (checkSelfPermission(android.Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && checkSelfPermission(android.Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
        return;
    }
    Location location = locationManager.getLastKnownLocation(mMapProvider);
    if (location != null){
        onLcatonChanged(location);
    }
    locationManager.requestLocationUpdates(mMapProvider, 20000, 0, (LocationListener) this);

}

private void onLcatonChanged(Location location) {

    double latitude = location.getLatitude();
    double longitude = location.getLongitude();
    LatLng latLng = new LatLng(latitude, longitude);
    googleMap.moveCamera(CameraUpdateFactory.newLatLng(latLng));
    googleMap.animateCamera(CameraUpdateFactory.zoomTo(15));
}}

下面给出的错误

process：com.example.rahul.maptask,pid：21986 java.lang.runtimeException：无法启动活动ComponentInfo{com.example.rahul.maptask/com.example.rahul.maptask.mainactivity}：java.lang.nullpointerException：试图在Android.app.activitythread.performLaunchActivity（ActivityThread.handleLaunchActivity（ActivityThread.2339)的.java:2413)在Android.app.activityThread.Access$800(activityThread.java:155)在Android.app.activityThread.h.h.handleMessage(activityThread.java:1317)在Android.os.handler.dispatchMessage(handler.java:102)在Android.os.handler.dispatchMessage(handler.java:135)在Android.app.activityThread.main（activityThread.java:5343)在

Answer 1

问题是因为地图在开始活动后还没有准备好。您必须从API中使用getMapAsync方法：

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

您的活动应该这样声明：

public class MainActivity extends FragmentActivity
    implements OnMapReadyCallback {
...
}

您必须实现回调，它以与在onCreate中相同的方式使用映射：

@Override
public void onMapReady(GoogleMap googleMap) {
    googleMap.setMyLocationEnabled(true);

    Criteria criteria = new Criteria();
    LocationManager locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);
    String mMapProvider = locationManager.getBestProvider(criteria, true);

    if (checkSelfPermission(android.Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && checkSelfPermission(android.Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
        return;
    }
    Location location = locationManager.getLastKnownLocation(mMapProvider);
    if (location != null){
         onLcatonChanged(location);
    }
    locationManager.requestLocationUpdates(mMapProvider, 20000, 0, (LocationListener) this);
}