我正在尝试在操作栏选项卡中实现 Maps v2。地图选项卡是从 MapFragment 继承的片段。单击地图选项卡后,应用程序强制关闭。它在调用 getMap() 的 onStart 方法中给出空指针异常。这是代码。请告诉我哪里错了。
public class MapActivity extends MapFragment implements LocationListener {
int mNum;
GoogleMap googleMap;
public static MapActivity newInstance() {
MapActivity f = new MapActivity();
// Supply num input as an argument.
Bundle args = new Bundle();
//args.putInt("num", num);
//f.setArguments(args);
return f;
}
/**
* When creating, retrieve this instance's number from its arguments.
*/
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.maplayout, container, false);
return v;
}
/**
* The Fragment's UI is just a simple text view showing its
* instance number.
*/
public void onStart(){
super.onStart();
googleMap=getMap();
// Enabling MyLocation Layer of Google Map
googleMap.setMyLocationEnabled(true);
getActivity();
// Getting LocationManager object from System Service LOCATION_SERVICE
LocationManager locationManager = (LocationManager)getActivity().getSystemService(Context.LOCATION_SERVICE);
// Creating a criteria object to retrieve provider
Criteria criteria = new Criteria();
// Getting the name of the best provider
String provider = locationManager.getBestProvider(criteria, true);
// Getting Current Location
Location location = locationManager.getLastKnownLocation(provider);
if(location!=null){
onLocationChanged(location);
}
locationManager.requestLocationUpdates(provider, 20000, 0, this);
// Setting a click event handler for the map
googleMap.setOnMapClickListener(new OnMapClickListener() {
@Override
public void onMapClick(LatLng latLng) {
// Creating a marker
MarkerOptions markerOptions = new MarkerOptions();
// Setting the position for the marker
markerOptions.position(latLng);
// Setting the title for the marker.
// This will be displayed on taping the marker
markerOptions.title(latLng.latitude + " : " + latLng.longitude);
// Clears the previously touched position
//googleMap.clear();
// Animating to the touched position
googleMap.animateCamera(CameraUpdateFactory.newLatLng(latLng));
// Placing a marker on the touched position
googleMap.addMarker(markerOptions);
}
});
}
@Override
public void onLocationChanged(Location location) {
TextView tvLocation = (TextView) getActivity().findViewById(R.id.tv_location);
// Getting latitude of the current location
double latitude = location.getLatitude();
// Getting longitude of the current location
double longitude = location.getLongitude();
// Creating a LatLng object for the current location
LatLng latLng = new LatLng(latitude, longitude);
// Showing the current location in Google Map
googleMap.moveCamera(CameraUpdateFactory.newLatLng(latLng));
// Zoom in the Google Map
googleMap.animateCamera(CameraUpdateFactory.zoomTo(15));
// Setting latitude and longitude in the TextView tv_location
tvLocation.setText("Latitude:" + latitude + ", Longitude:"+ longitude );
}
@Override
public void onProviderDisabled(String provider) {
// TODO Auto-generated method stub
}
@Override
public void onProviderEnabled(String provider) {
// TODO Auto-generated method stub
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
// TODO Auto-generated method stub
}
}
编辑:我认为这段代码不应该写在 onStart 方法中,因为那时地图没有显示。如何知道地图已经加载,获取它的对象?