Question

我的问题是此代码中的空指针异常：

public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_maps, null, false);

    FragmentTransaction ft = getFragmentManager().beginTransaction();


    mMap = ((SupportMapFragment) getFragmentManager().findFragmentById(R.id.map)).getMap();

    SupportMapFragment fmap = (SupportMapFragment) getFragmentManager().findFragmentById(R.id.map);

    if (fmap == null) {
        fmap = SupportMapFragment.newInstance();
        ft.add(R.id.map, fmap);
    }

    ft.commit();

正是在这一点上：

mMap = ((SupportMapFragment) getFragmentManager().findFragmentById(R.id.map)).getMap();

我已经测试了某种类型的解决方案，但都不起作用。

发布我片段的所有代码：

public class mapsFragment extends SupportMapFragment {

private GoogleMap mMap; // Might be null if Google Play services APK is not available.
LocationManager manager;
Location loca;

String lati;
String longi;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_maps, null, false);

    FragmentTransaction ft = getFragmentManager().beginTransaction();

    mMap = ((SupportMapFragment) getFragmentManager().findFragmentById(R.id.map)).getMap();

    SupportMapFragment fmap = (SupportMapFragment) getFragmentManager().findFragmentById(R.id.map);

    if (fmap == null) {
        fmap = SupportMapFragment.newInstance();
        ft.add(R.id.map, fmap);
    }

    ft.commit();

    manager = (LocationManager) getActivity().getSystemService(Context.LOCATION_SERVICE);

    Criteria criteria = new Criteria();
    criteria.setAccuracy(Criteria.ACCURACY_FINE);
    criteria.setAltitudeRequired(false);
    criteria.setBearingRequired(false);
    criteria.setCostAllowed(true);
    criteria.setPowerRequirement(Criteria.POWER_MEDIUM);
    String  provider = manager.getBestProvider(criteria,true);

    manager.requestLocationUpdates(provider, 0, 0, locationListener);
    loca = manager.getLastKnownLocation(provider);

    if(loca != null) {
        CameraPosition cameraPosition = new CameraPosition.Builder()
                .target(new LatLng(loca.getLatitude(), loca.getLongitude()))      // Sets the center of the map to location user
                .zoom(16)                   // Sets the zoom
                .tilt(40)                   // Sets the tilt of the camera to 30 degrees
                .build();                   // Creates a CameraPosition from the builder
        mMap.animateCamera(CameraUpdateFactory.newCameraPosition(cameraPosition));
    }

    if (!manager.isProviderEnabled(LocationManager.GPS_PROVIDER)) {
        buildAlertMessageNoGps();
    }


    return rootView;
}

private final LocationListener locationListener = new LocationListener() {

    @Override
    public void onStatusChanged(String provider, int status, Bundle extras) {
        // TODO Auto-generated method stub
    }

    @Override
    public void onProviderEnabled(String provider) {
        // TODO Auto-generated method stub
    }

    @Override
    public void onProviderDisabled(String provider) {
    }

    @Override
    public void onLocationChanged(Location location) {
        insertMarker(location);
    }
};


/**
 * This is where we can add markers or lines, add listeners or move the camera. In this case, we
 * just add a marker near Africa.
 * <p/>
 * This should only be called once and when we are sure that {@link #mMap} is not null.
 */
private void setUpMap() {
    mMap.setMyLocationEnabled(true);
    mMap.getUiSettings().setZoomControlsEnabled(true);
    mMap.getUiSettings().setCompassEnabled(true);
}



public void insertMarker(Location location) {
    if(location != null){

        double lat = location.getLatitude();
        double lng = location.getLongitude();
        lati = String.valueOf(lat);
        longi = String.valueOf(lng);
        mMap.addMarker(new MarkerOptions().position(new LatLng(lat, lng)).title(lati + " , " + longi));

    }else{

        lati = "Latitudine non trovata";
        longi = "Longitudine non trovata";

    }
}

private void buildAlertMessageNoGps() {
    final AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
    builder.setMessage("Il tuo GPS è disabilitato, vuoi attivarlo?")
            .setCancelable(false)
            .setPositiveButton("Yes", new DialogInterface.OnClickListener() {
                public void onClick(@SuppressWarnings("unused") final DialogInterface dialog, @SuppressWarnings("unused") final int id) {
                    startActivity(new Intent(android.provider.Settings.ACTION_LOCATION_SOURCE_SETTINGS));
                }
            })
            .setNegativeButton("No", new DialogInterface.OnClickListener() {
                public void onClick(final DialogInterface dialog, @SuppressWarnings("unused") final int id) {
                    getActivity().finish();
                }
            });
    final AlertDialog alert = builder.create();
    alert.show();
}

}

全部谢谢：）

Answer 1

您可能希望将该行更改为

mMap = ((SupportMapFragment) getChildFragmentManager().findFragmentById(R.id.map)).getMap();

或

mMap =((SupportMapFragment)getActivity().getSupportFragmentManager().findFragmentById(R.id.map)).getMap();

因为您应该在活动中调用getFragmentManager()。

mMap = findFragmentById（R.id.map））。getMap（）;别＆＃39;在片段中工作并给出nullpointer

1 个答案: