錯誤getMap（）;

Question

我在這行代碼中有錯誤（72）。我已經在論壇上搜索過，但還沒有解決，我試圖改變爲getMapAsync（）;

看來，這個功能已經過時了，但因爲我在互聯網上找到的這個代碼，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 
    } 
} 

Answer 1

的問題是，在運行時onCreate地圖實例化沒有完成。當您收到Map完成加載的回調時，您必須根據地圖開始您的任務。

Answer 2

你應該嘗試的地圖異步，這樣的事情：

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 
     } 
    } 

你可能會得到錯誤becouse地圖還沒有準備好，當你調用的GetMap（），你會得到空。爲了防止它，你總是得到地圖異步，當它準備好，做一些操作。