如何在设置新航路点后删除以前的多段线谷歌Mapandroid工作室

我是新来的安卓工作室，我学习了几天。我试图实现一个Map，我们可以设置两个标记来找到他们之间的路线。今天我试着实现他们之间的航路点。在Map中设置航路点后，两个标记之间的旧路线（即从起点到目的地）不会被删除。我得到的是从起点到航点再到目的地的旧路线和新路线。注意：我正在尝试实现两个航路点，因此如果我设置一个航路点，它将显示新路线（起始航路点-目的地），如果我设置两个航路点，它将显示新路线（起始航路点-航路点1-目的地），删除旧路线。
代码如下：Map活动
'''公共类mapsactivity扩展了fragmentactivity实现onmapreadycallback{

private GoogleMap mMap;
ArrayList markerPoints = new ArrayList();

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

@Override
public void onMapReady(GoogleMap googleMap) {
    mMap = googleMap;
    LatLng chennai = new LatLng(13.04984411, 80.21033674);
    //mMap.addMarker(new MarkerOptions().position(chennai).title("Marker in chennai"));
    mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(chennai,16));

    mMap.setOnMapClickListener(new GoogleMap.OnMapClickListener() {
        @Override
        public void onMapClick(LatLng latLng) {

            if (markerPoints.size() > 3) {
                markerPoints.clear();
                mMap.clear();
            }

            // Adding new item to the ArrayList
            markerPoints.add(latLng);

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

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

            if (markerPoints.size() == 1) {
                options.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_GREEN));
            } else if (markerPoints.size() == 2) {
                options.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_RED));
            } else if(markerPoints.size() == 3){
                options.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_ORANGE));
            } else {
                options.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_BLUE));
            }
            // Add new marker to the Google Map Android API V2
            mMap.addMarker(options);

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

    //waypoints
    String waypoints = "";
    for(int i=2;i<markerPoints.size();i++){
        LatLng point  = (LatLng) markerPoints.get(i);
        LatLng point1 = (LatLng) markerPoints.get(i);
        if(i==2) {
            waypoints = "waypoints=optimize:true|via:";
            waypoints += point.latitude + "%2C" + point.longitude + "%7C";
        } else if(i==3) {
            waypoints = "waypoints=optimize:true|via:";
            waypoints += point.latitude + "%2C" + point.longitude + "%7C" + "via:" + point1.latitude + "%2C" + point1.longitude + "%7C";
        }
    }

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

    // Output format
    String output = "json";

    // Building the url to the web service
    String url = "https://maps.googleapis.com/maps/api/directions/" + output + "?" + parameters + "&" + "key=AIzaSyBFrVlAmYqllaDiFZFfr62aLKZoOoP9xdo";

    return url;
}

private class DownloadTask extends AsyncTask<String, Void, String> {

    @Override
    protected String doInBackground(String... url) {

        String data = "";

        try {
            data = downloadUrl(url[0]);
        } catch (Exception e) {
            Log.d("Background Task", e.toString());
        }
        return data;
    }

    @Override
    protected void onPostExecute(String result) {
        super.onPostExecute(result);

        ParserTask parserTask = new ParserTask();
        parserTask.execute(result);

    }
}

/**
 * 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);

        urlConnection = (HttpURLConnection) url.openConnection();

        urlConnection.connect();

        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", e.toString());
    } finally {
        iStream.close();
        urlConnection.disconnect();
    }
    return data;
}

/**
 * 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();

            routes = parser.parse(jObject);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return routes;
    }

    @Override
    protected void onPostExecute(List<List<HashMap<String, String>>> result) {
        ArrayList<LatLng> points = null;
        PolylineOptions lineOptions = null;

        for (int i = 0; i < result.size(); i++) {
            points = new ArrayList<>();
            lineOptions = new PolylineOptions();

            List<HashMap<String, String>> path = result.get(i);

            for (int j = 0; j < path.size(); j++) {
                HashMap<String, String> point = path.get(j);

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

                points.add(position);
            }

            lineOptions.addAll(points);
            lineOptions.width(12);
            lineOptions.color(Color.RED);
            lineOptions.geodesic(true);
        }
        if(lineOptions != null)
            mMap.addPolyline(lineOptions);
    }
}

方向JSONParser:：
公共类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;
    JSONArray jLegs;
    JSONArray jSteps;

    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 : http://jeffreysambells.com/2010/05/27/decoding-polylines-from-google-maps-direction-api-with-java
 * */
private List decodePoly(String encoded) {

    List poly = new ArrayList();
    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;
}

如何在设置新航路点后删除以前的多段线谷歌Mapandroid工作室

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