错误 getMap();

Posted 2023-04-14

【中文标题】错误 getMap();

【英文标题】：Error getMap();

【发布时间】：2017-11-23 04:00:10

【问题描述】：

我在这行代码中有一个错误 (72)。我已经在论坛里搜索过了，还没有解决，我试着改成getMapAsync();

这个功能似乎已经过时了，但是我在互联网上找到了这个代码，我不知道如何更新它。

http://wptrafficanalyzer.in/blog/driving-route-from-my-location-to-destination-in-google-maps-android-api-v2/

public class MapsActivity extends FragmentActivity implements LocationListener 

    GoogleMap mGoogleMap;
    ArrayList<LatLng> mMarkerPoints;
    double mLatitude = 0;
    double mLongitude = 0;

    @Override
    protected void onCreate(Bundle savedInstanceState) 
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_maps);

        // Getting Google Play availability status
        int status = GooglePlayServicesUtil.isGooglePlayServicesAvailable(getBaseContext());

        if (status != ConnectionResult.SUCCESS)  // Google Play Services are not available

            int requestCode = 10;
            Dialog dialog = GooglePlayServicesUtil.getErrorDialog(status, this, requestCode);
            dialog.show();

         else  // Google Play Services are available

            // Initializing
            mMarkerPoints = new ArrayList<LatLng>();

            // Getting reference to SupportMapFragment of the activity_main
            SupportMapFragment fm = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);

            // Getting Map for the SupportMapFragment
            mGoogleMap = fm.getMap();

            // Enable MyLocation Button in the Map
            if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) 
                // TODO: Consider calling
                //    ActivityCompat#requestPermissions
                // here to request the missing permissions, and then overriding
                //   public void onRequestPermissionsResult(int requestCode, String[] permissions,
                //                                          int[] grantResults)
                // to handle the case where the user grants the permission. See the documentation
                // for ActivityCompat#requestPermissions for more details.
                return;
            
            mGoogleMap.setMyLocationEnabled(true);


            // Getting LocationManager object from System Service LOCATION_SERVICE
            LocationManager locationManager = (LocationManager) getSystemService(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 From GPS
            Location location = locationManager.getLastKnownLocation(provider);

            if(location!=null)
                onLocationChanged(location);
            

            locationManager.requestLocationUpdates(provider, 20000, 0, this);

            // Setting onclick event listener for the map
            mGoogleMap.setOnMapClickListener(new GoogleMap.OnMapClickListener() 

                @Override
                public void onMapClick(LatLng point) 

                    // Already map contain destination location
                    if(mMarkerPoints.size()>1)

                        FragmentManager fm = getSupportFragmentManager();
                        mMarkerPoints.clear();
                        mGoogleMap.clear();
                        LatLng startPoint = new LatLng(mLatitude, mLongitude);
                        drawMarker(startPoint);
                    

                    drawMarker(point);

                    // Checks, whether start and end locations are captured
                    if(mMarkerPoints.size() >= 2)
                        LatLng origin = mMarkerPoints.get(0);
                        LatLng dest = mMarkerPoints.get(1);

                        // Getting URL to the Google Directions API
                        String url = getDirectionsUrl(origin, dest);

                        DownloadTask downloadTask = new DownloadTask();

                        // Start downloading json data from Google Directions API
                        downloadTask.execute(url);
                    
                
            );
        
    

    private String getDirectionsUrl(LatLng origin,LatLng dest)

        // Origin of route
        String str_origin = "origin="+origin.latitude+","+origin.longitude;

        // Destination of route
        String str_dest = "destination="+dest.latitude+","+dest.longitude;
        String sensor = "sensor=false";

        // Sensor enabled

        // Building the parameters to the web service
        String parameters = str_origin+"&"+str_dest+"&"+sensor;

        // Output format
        String output = "json";

        // Building the url to the web service
        String url = "https://maps.googleapis.com/maps/api/directions/"+output+"?"+parameters;

        return url;
    

    /** A method to download json data from url */
    private String downloadUrl(String strUrl) throws IOException 
        String data = "";
        InputStream iStream = null;
        HttpURLConnection urlConnection = null;
        try
            URL url = new URL(strUrl);

            // Creating an http connection to communicate with url
            urlConnection = (HttpURLConnection) url.openConnection();

            // Connecting to url
            urlConnection.connect();

            // Reading data from url
            iStream = urlConnection.getInputStream();

            BufferedReader br = new BufferedReader(new InputStreamReader(iStream));

            StringBuffer sb  = new StringBuffer();

            String line = "";
            while( ( line = br.readLine())  != null)
                sb.append(line);
            

            data = sb.toString();

            br.close();

        catch(Exception e)
            Log.d("Exception while downloading url", e.toString());
        finally
            iStream.close();
            urlConnection.disconnect();
        
        return data;
    



    /** A class to download data from Google Directions URL */
    private class DownloadTask extends AsyncTask<String, Void, String> 

        // Downloading data in non-ui thread
        @Override
        protected String doInBackground(String... url) 

            // For storing data from web service
            String data = "";

            try
                // Fetching the data from web service
                data = downloadUrl(url[0]);
            catch(Exception e)
                Log.d("Background Task",e.toString());
            
            return data;
        

        // Executes in UI thread, after the execution of
        // doInBackground()
        @Override
        protected void onPostExecute(String result) 
            super.onPostExecute(result);

            ParserTask parserTask = new ParserTask();

            // Invokes the thread for parsing the JSON data
            parserTask.execute(result);

        
    

    /** A class to parse the Google Directions in JSON format */
    private class ParserTask extends AsyncTask<String, Integer, List<List<HashMap<String,String>>> >

        // Parsing the data in non-ui thread
        @Override
        protected List<List<HashMap<String, String>>> doInBackground(String... jsonData) 

            JSONObject jObject;
            List<List<HashMap<String, String>>> routes = null;

            try
                jObject = new JSONObject(jsonData[0]);
                DirectionsJSONParser parser = new DirectionsJSONParser();

                // Starts parsing data
                routes = parser.parse(jObject);
            catch(Exception e)
                e.printStackTrace();
            
            return routes;
        

        // Executes in UI thread, after the parsing process
        @Override
        protected void onPostExecute(List<List<HashMap<String, String>>> result) 
            ArrayList<LatLng> points = null;
            PolylineOptions lineOptions = null;

            // Traversing through all the routes
            for(int i=0;i<result.size();i++)
                points = new ArrayList<LatLng>();
                lineOptions = new PolylineOptions();

                // Fetching i-th route
                List<HashMap<String, String>> path = result.get(i);

                // Fetching all the points in i-th route
                for(int j=0;j<path.size();j++)
                    HashMap<String,String> point = path.get(j);

                    double lat = Double.parseDouble(point.get("lat"));
                    double lng = Double.parseDouble(point.get("lng"));
                    LatLng position = new LatLng(lat, lng);

                    points.add(position);
                

                // Adding all the points in the route to LineOptions
                lineOptions.addAll(points);
                lineOptions.width(2);
                lineOptions.color(Color.RED);

            

            // Drawing polyline in the Google Map for the i-th route
            mGoogleMap.addPolyline(lineOptions);
        
    


    private void drawMarker(LatLng point)
        mMarkerPoints.add(point);

        // Creating MarkerOptions
        MarkerOptions options = new MarkerOptions();

        // Setting the position of the marker
        options.position(point);

        /**
         * For the start location, the color of marker is GREEN and
         * for the end location, the color of marker is RED.
         */
        if(mMarkerPoints.size()==1)
            options.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_GREEN));
        else if(mMarkerPoints.size()==2)
            options.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_RED));
        

        // Add new marker to the Google Map Android API V2
        mGoogleMap.addMarker(options);
    

    @Override
    public void onLocationChanged(Location location) 
        // Draw the marker, if destination location is not set
        if(mMarkerPoints.size() < 2)

            mLatitude = location.getLatitude();
            mLongitude = location.getLongitude();
            LatLng point = new LatLng(mLatitude, mLongitude);

            mGoogleMap.moveCamera(CameraUpdateFactory.newLatLng(point));
            mGoogleMap.animateCamera(CameraUpdateFactory.zoomTo(12));

            drawMarker(point);
        

    

    @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
    

【参考方案1】：

问题是在运行onCreate 时地图实例化没有完成。当您收到Map 加载完成的回调时，您必须根据地图开始您的任务。

【讨论】：

它可以举例说明我应该在哪里改变我是 android 新手。

【参考方案2】：

你应该尝试让地图异步，类似这样：

public class FindLocationActivity extends AppCompatActivity implements
            OnMapReadyCallback 

        private GoogleMap map;

        @Override
        protected void onCreate(Bundle savedInstanceState) 
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_find_location);

            SupportMapFragment mapFragment =
                    (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
            mapFragment.getMapAsync(this);
        

        @Override
        public void onMapReady(GoogleMap map) 
            this.map = map;
            //from this moment do whatever you want to do with map
        
    

你得到错误可能是因为当你调用 getMap() 时地图还没有准备好并且你得到空值。为了防止它发生，你应该总是让地图异步，当它准备好时，对它进行一些操作。