谷歌地图 API v2 的 java.lang.NullPointerException

Question

多年来我一直在尝试解决这个问题，但我找不到问题出在哪里。我只在某些运行 Android 2.2 的设备上遇到问题。我在 Android 4.1.2 上测试过，它运行良好。

我得到的错误:

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.coldice.plotfinder/com.coldice.plotfinder.MapFragment}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2668)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2684)
at android.app.ActivityThread.access$2300(ActivityThread.java:126)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2038)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:123)
at android.app.ActivityThread.main(ActivityThread.java:4632)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:521)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.coldice.plotfinder.MapFragment.onCreate(MapFragment.java:67)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2632)
... 11 more

所以回顾我的类 MapFragment 第 67 行是

 googleMap.setMapType(GoogleMap.MAP_TYPE_SATELLITE);

我知道 googlemap API v2 需要 API 级别 12 或更高级别 as noted here , 但我用的是 lower 所以我调用

getSupportFragmentManager();

MapFragment类代码如下:

public class MapFragment extends SherlockFragmentActivity {
    private static final String TAG = "MapFragment";
    private GoogleMap googleMap;                                                    // Google map 
    private int mapType = GoogleMap.MAP_TYPE_SATELLITE;

    private Polyline polyline;;                                                     // Drawing the area of the land by using the polygon
    private boolean isDrawn=false;
    static String fileToBeRead =null;                                               // The file name to be read

    ArrayList<Cooridnates> cooridnatesList;
    // Image utility saving
    ImageSaveUtil imageUtil = new ImageSaveUtil();

    @Override
    public void onCreate(Bundle savedInstanceState) {
        setTheme(R.style.Theme_Sherlock);
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_map);

        // Different colors for each marker
        float[] markerColours = {BitmapDescriptorFactory.HUE_AZURE,BitmapDescriptorFactory.HUE_BLUE,BitmapDescriptorFactory.HUE_CYAN,BitmapDescriptorFactory.HUE_GREEN,
        BitmapDescriptorFactory.HUE_MAGENTA,BitmapDescriptorFactory.HUE_ORANGE,BitmapDescriptorFactory.HUE_RED,BitmapDescriptorFactory.HUE_ROSE,
        BitmapDescriptorFactory.HUE_VIOLET,BitmapDescriptorFactory.HUE_YELLOW};

        // The code I am getting java.lang.NullPointerException
        FragmentManager fragmentManager = getSupportFragmentManager();
        SupportMapFragment mapFragment =  (SupportMapFragment)fragmentManager.findFragmentById(R.id.map);
        googleMap = mapFragment.getMap();
        googleMap.setMapType(GoogleMap.MAP_TYPE_SATELLITE);

        // If there is a file to be read, then read the coordinates 
        if(fileToBeRead!=null)
        {
            readData(fileToBeRead);
            fileToBeRead =null;
        }

            // Getting the coordinates List
        cooridnatesList = MainActivity.getList();
        if(cooridnatesList!=null)
        {
            // Adding a marker from each point
            for(int i=0;i<cooridnatesList.size();i++)
            {
                LatLng point = new LatLng(cooridnatesList.get(i).getLat(),cooridnatesList.get(i).getLon());
                googleMap.addMarker(new MarkerOptions()
                .position(point)
                .title("My Land")
                .snippet("Point: "+cooridnatesList.get(i).getLat()+","+cooridnatesList.get(i).getLon())
                .icon(BitmapDescriptorFactory.defaultMarker(markerColours[i%10])));

            }

            googleMap.getUiSettings().setCompassEnabled(true);                      // Setting the compass enabled in the map
            googleMap.getUiSettings().setZoomControlsEnabled(true);                 // Zooming is enabled
            googleMap.getUiSettings().setMyLocationButtonEnabled(true);             // My location button is enabled


            // Zooming the camera from the first point entered 
            LatLng cameraLatLng = new LatLng(cooridnatesList.get(0).getLat(),cooridnatesList.get(0).getLon());
            float cameraZoom = 10;

            if(savedInstanceState != null){
                mapType = savedInstanceState.getInt("map_type", GoogleMap.MAP_TYPE_SATELLITE);

                double savedLat = savedInstanceState.getDouble("lat");
                double savedLng = savedInstanceState.getDouble("lng");
                cameraLatLng = new LatLng(savedLat, savedLng);

                cameraZoom = savedInstanceState.getFloat("zoom",18);
            }

            // Setting the map type such as satellites or street view
            googleMap.setMapType(mapType);
            googleMap.animateCamera(CameraUpdateFactory.newLatLngZoom(cameraLatLng, cameraZoom));


            //Displaying the land area
            final TextView landInformation = (TextView)findViewById(R.id.textViewLandInformation);
            double area = calculateArea(cooridnatesList);
            landInformation.setText(getString(R.string.land_area)+"\n"+Math.round(area)+" SQ.M");

        }

    }

Answer 1

尝试将所有引用您的 GoogleMap 的代码移动到 onStart() 或 onResume()。直到 fragment 通过 onCreateView ( link ) 之后， map fragment 中的 map 才会被实例化。此外，您需要检查您的 googleMap 是否为 null，因为如果未安装 google play 服务，或者由于其他原因 map 不可用，它将为 null。