我正在制作一个 android studio 应用程序，用户可以在其中看到两个位置点之间的最佳排序路径。我使用 Normal android studio map frame 和 SupportMapFragment 来显示谷歌地图。我想在多个航点中找到最佳路线。这些是我的 android 应用程序的文件。此项目文件 MapsActivity.java 文件中只有一个问题 getmap 方法不起作用。还有其他开发方法吗？

    public class MapsActivity extends FragmentActivity {

        GoogleMap map;
        ArrayList<LatLng> markerPoints;

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

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

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

            // Getting reference to Button
            Button btnDraw = (Button)findViewById(R.id.btn_draw);

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

            // Enable MyLocation Button in the Map
            map.setMyLocationEnabled(true);

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

                @Override
                public void onMapClick(LatLng point) {

                    // Already 10 locations with 8 waypoints and 1 start location and 1 end location.
                    // Upto 8 waypoints are allowed in a query for non-business users
                    if(markerPoints.size()>=10){
                        return;
                    }

                    // Adding new item to the ArrayList
                    markerPoints.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 and
                     * for the rest of markers, the color is AZURE
                     */
                    if(markerPoints.size()==1){
                        options.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_GREEN));
                    }else if(markerPoints.size()==2){
                        options.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_RED));
                    }else{
                        options.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_AZURE));
                    }

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

            // The map will be cleared on long click
            map.setOnMapLongClickListener(new GoogleMap.OnMapLongClickListener() {

                @Override
                public void onMapLongClick(LatLng point) {
                    // Removes all the points from Google Map
                    map.clear();

                    // Removes all the points in the ArrayList
                    markerPoints.clear();
                }
            });

            // Click event handler for Button btn_draw
            btnDraw.setOnClickListener(new View.OnClickListener() {

                @Override
                public void onClick(View v) {
                    // Checks, whether start and end locations are captured
                    if(markerPoints.size() >= 2){
                        LatLng origin = markerPoints.get(0);
                        LatLng dest = markerPoints.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;

            // Sensor enabled
            String sensor = "sensor=false";

            // Waypoints
            String waypoints = "";
            for(int i=2;i<markerPoints.size();i++){
                LatLng point  = (LatLng) markerPoints.get(i);
                if(i==2)
                    waypoints = "waypoints=";
                waypoints += point.latitude + "," + point.longitude + "|";
            }

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

            // 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;
        }

        // Fetches data from url passed
        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 Places 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
                map.addPolyline(lineOptions);
            }
        }
        }

其他文件DirectionsJSONParser.java

public class DirectionsJSONParser {

    /**
     * Receives a JSONObject and returns a list of lists containing latitude and longitude
     */
    public List<List<HashMap<String, String>>> parse(JSONObject jObject) {

        List<List<HashMap<String, String>>> routes = new ArrayList<List<HashMap<String, String>>>();
        JSONArray jRoutes = null;
        JSONArray jLegs = null;
        JSONArray jSteps = null;

        try {

            jRoutes = jObject.getJSONArray("routes");

            /** Traversing all routes */
            for (int i = 0; i < jRoutes.length(); i++) {
                jLegs = ((JSONObject) jRoutes.get(i)).getJSONArray("legs");
                List path = new ArrayList<HashMap<String, String>>();

                /** Traversing all legs */
                for (int j = 0; j < jLegs.length(); j++) {
                    jSteps = ((JSONObject) jLegs.get(j)).getJSONArray("steps");

                    /** Traversing all steps */
                    for (int k = 0; k < jSteps.length(); k++) {
                        String polyline = "";
                        polyline = (String) ((JSONObject) ((JSONObject) jSteps.get(k)).get("polyline")).get("points");
                        List<LatLng> list = decodePoly(polyline);

                        /** Traversing all points */
                        for (int l = 0; l < list.size(); l++) {
                            HashMap<String, String> hm = new HashMap<String, String>();
                            hm.put("lat", Double.toString(((LatLng) list.get(l)).latitude));
                            hm.put("lng", Double.toString(((LatLng) list.get(l)).longitude));
                            path.add(hm);
                        }
                    }
                    routes.add(path);
                }
            }
        } catch (JSONException e) {
            e.printStackTrace();
        } catch (Exception e) {
        }
        return routes;
    }

    /**
     * Method to decode polyline points
     * Courtesy : jeffreysambells.com/2010/05/27/decoding-polylines-from-google-maps-direction-api-with-java
     */
    private List<LatLng> decodePoly(String encoded) {

        List<LatLng> poly = new ArrayList<LatLng>();
        int index = 0, len = encoded.length();
        int lat = 0, lng = 0;

        while (index < len) {
            int b, shift = 0, result = 0;
            do {
                b = encoded.charAt(index++) - 63;
                result |= (b & 0x1f) << shift;
                shift += 5;
            } while (b >= 0x20);
            int dlat = ((result & 1) != 0 ? ~(result >> 1) : (result >> 1));
            lat += dlat;

            shift = 0;
            result = 0;
            do {
                b = encoded.charAt(index++) - 63;
                result |= (b & 0x1f) << shift;
                shift += 5;
            } while (b >= 0x20);
            int dlng = ((result & 1) != 0 ? ~(result >> 1) : (result >> 1));
            lng += dlng;

            LatLng p = new LatLng((((double) lat / 1E5)),
                    (((double) lng / 1E5)));
            poly.add(p);
        }

        return poly;
    }
}

其他文件activity_maps.xml

<RelativeLayout 
android:layout_width="match_parent"
android:layout_height="match_parent"
 >

<Button
    android:id="@+id/btn_draw"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:layout_centerHorizontal="true" />

<fragment
    android:id="@+id/map"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_above="@id/btn_draw" />

</RelativeLayout>

最佳答案

要获取 map ，请使用:

// Obtain the SupportMapFragment and get notified when the map is ready to be used.
    SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
            .findFragmentById(R.id.map);
    mapFragment.getMapAsync(this);

您的 Activity 必须实现 OnMapReadyCallback 并覆盖 onMapReady(GoogleMap googleMap) 函数。

public class MapsActivity extends FragmentActivity implements OnMapReadyCallback{
     .....

@Override
public void onMapReady(GoogleMap googleMap) {
    mMap = googleMap;

   }

 }

参见 Getting Started指导。

关于android - Google Map Android Studio 中具有多个航路点的两个位置之间的最佳路线，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/45530621/