java - Mapbox 无法在 fragment 中工作

Question

我试图在 fragment 中显示 map 框，但出现以下错误:

java.lang.NullPointerException:尝试在空对象引用上调用虚方法“void com.mapbox.mapboxsdk.maps.MapView.onResume()”

这是 map fragment 类:

public class Map extends android.support.v4.app.Fragment {
    private MapView mapView;

public Map() {
    // Required empty public constructor
}


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

    MapView mapView = (MapView) layout.findViewById(R.id.mapview);
    mapView.onCreate(savedInstanceState);
    mapView.getMapAsync(new OnMapReadyCallback() {
        @Override
        public void onMapReady(MapboxMap mapboxMap) {

            // Set map style
            mapboxMap.setStyleUrl(Style.MAPBOX_STREETS);

            // Set the camera's starting position
            CameraPosition cameraPosition = new CameraPosition.Builder()
                    .target(new LatLng(41.885, -87.679)) // set the camera's center position
                    .zoom(12)  // set the camera's zoom level
                    .tilt(20)  // set the camera's tilt
                    .build();

            // Move the camera to that position
            mapboxMap.moveCamera(CameraUpdateFactory.newCameraPosition(cameraPosition));

        }


    });
    return layout;
}

@Override
public void onResume() {
    super.onResume();
    mapView.onResume();
}

@Override
public void onPause() {
    super.onPause();
    mapView.onPause();
}

@Override
public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    mapView.onSaveInstanceState(outState);
}

@Override
public void onLowMemory() {
    super.onLowMemory();
    mapView.onLowMemory();
}

@Override
public void onDestroy() {
    super.onDestroy();
    mapView.onDestroy();
}
}

我是不是漏掉了什么？我正在关注此链接:https://www.mapbox.com/help/first-steps-android-sdk/

Answer 1

您有两个 map View 实例。一个是 oncreate 方法内部的局部变量，另一个是全局变量。

并且全局变量没有初始化，所以改变这一行

MapView mapView = (MapView) layout.findViewById(R.id.mapview);

进入这个

mapView = (MapView) layout.findViewById(R.id.mapview);

我想你明白这个问题了。