Question

我的应用中有一项活动，其中显示了Google地图，还有一些其他功能可供选择。该活动名为MapActivity，并扩展为FragmentActivity。

public class MapActivity extends FragmentActivity implements OnMapReadyCallback {

    private GoogleMap googleMap;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_map);

    initializeMap();
    }

    private void initializeMap() {
        if (googleMap == null) {
            MapFragment mapFragment = (MapFragment) getFragmentManager().findFragmentById(R.id.map);
            if(mapFragment!=null){
                mapFragment.getMapAsync(MapActivity.this);
            }

            // check if map is created successfully or not
            if (null== googleMap) {
                Toast.makeText(getApplicationContext(), "Sorry! unable to create maps", Toast.LENGTH_SHORT).show();
            }
        }
    }

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

但是当启动此活动时，应用程序崩溃，因为它在initializeMap方法中的mapFragment对象返回null。由于getMap()已被弃用且getMapAsync()方法被使用，但我自己的mapFragment对象为null，因此出现此错误。

如何对地图片段进行充气以避免此NullPointerException？

Answer 1

public class MapsActivity extends FragmentActivity implements OnMapReadyCallback {

    private GoogleMap mMap;

    @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;

        // Add a marker in Sydney and move the camera
        LatLng sydney = new LatLng(-34, 151);
        mMap.addMarker(new MarkerOptions().position(sydney).title("Marker in Sydney"));
        mMap.moveCamera(CameraUpdateFactory.newLatLng(sydney));
    }
}

MapFragment中的NullPointerException; FragmentActivity中的GoogleMap

1 个答案: