Java 在谷歌地图片段中绘制路径，并显示它，然后计算距离

我是android的新手，这是我的代码，问题是这个代码不能在地图上画出路径

这是我的主要活动

import android.graphics.Color;
import android.location.Location;
import android.location.LocationListener;

import android.location.LocationManager;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.widget.Toast;

import com.google.android.gms.maps.CameraUpdate;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.MapFragment;
import com.google.android.gms.maps.OnMapReadyCallback;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.Polyline;
import com.google.android.gms.maps.model.PolylineOptions;

import org.w3c.dom.Document;

import java.util.ArrayList;


public class servicing extends AppCompatActivity implements OnMapReadyCallback, LocationListener {

    protected GoogleMap mMap;
    String lang = "english";
    String test = "test";

    protected LocationManager locationManager;

    Route route = new Route();


    LatLng latLng1 = new LatLng(26.903291,75.792482);
    LatLng latLng2 = new LatLng(26.907708,75.806044);

    ArrayList<LatLng> points = new ArrayList<>(2);


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

        //GMapV2Direction md = new GMapV2Direction();

        MapFragment mapFragment = (MapFragment) getFragmentManager().findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);

        /*Document doc = md.getDocument(latLng1, latLng2,
                GMapV2Direction.MODE_DRIVING);


        ArrayList<LatLng> directionPoint = md.getDirection(doc);
        PolylineOptions rectLine = new PolylineOptions().width(3).color(
                Color.RED);

        for (int i = 0; i < directionPoint.size(); i++) {
            rectLine.add(directionPoint.get(i));
        }
        Polyline polylin = mMap.addPolyline(rectLine);*/

        points.add(latLng1);
        points.add(latLng2);


        route.drawRoute(mMap, this, points, true, lang, false);

        Toast.makeText(getApplicationContext(),driverdata.extrastmt,Toast.LENGTH_LONG).show();

        //route.drawRoute(mMap,this,latLng1,latLng2,lang);

    }

    @Override
    public void onMapReady(GoogleMap googleMap){
        mMap = googleMap;
        mMap.setMyLocationEnabled(true);
        mMap.animateCamera(CameraUpdateFactory.zoomTo(15), 2000, null);

        CameraUpdate cameraUpdate = CameraUpdateFactory.newLatLngZoom((latLng1),15);
        mMap.animateCamera(cameraUpdate);
        //route.drawRoute(mMap, this, points, true, lang, false);
    }

    @Override
    public void onProviderEnabled(String provider) {
        (Toast.makeText(getApplication(), "Reconnecting", Toast.LENGTH_LONG)).show();

    }

    @Override
    public void onProviderDisabled(String provider) {


        Toast.makeText(getApplication(),"Connection Failed! Check Network!",Toast.LENGTH_LONG).show();
    }

    @Override
    public void onStatusChanged(String provider, int status, Bundle extras) {
        Log.d("Latitude", "status");
    }

    @Override
    public void onLocationChanged(Location location) {
        Log.d("Latitude", "status");



    }


}

---

请告诉我需要帮助，而且它会获取数据，但在地图活动（即服务活动）上toast不会传递任何信息，一旦您按下back，然后再次按下on按钮开始服务活动，toast会传递以前的结果，但地图上看不到任何路线。

我找到了解决方案，基本上，我是在调用route.drawroute（），在将点添加到列表之前，它返回null。

我找到了解决方案，基本上，我调用了route.drawroute（），在将点添加到列表之前，它返回null。

看看这个答案：看看这个答案：

public class Route {
    GoogleMap mMap;
    Context context;
    String lang;


    static String LANGUAGE_SPANISH = "es";
    static String LANGUAGE_ENGLISH = "en";
    static String LANGUAGE_FRENCH = "fr";
    static String LANGUAGE_GERMAN = "de";
    static String LANGUAGE_CHINESE_SIMPLIFIED = "zh-CN";
    static String LANGUAGE_CHINESE_TRADITIONAL = "zh-TW";

    static String TRANSPORT_DRIVING = "driving";
    static String TRANSPORT_WALKING = "walking";
    static String TRANSPORT_BIKE = "bicycling";
    static String TRANSPORT_TRANSIT = "transit";


    public boolean drawRoute(GoogleMap map, Context c, ArrayList<LatLng> points, boolean withIndications, String language, boolean optimize)
    {
        mMap = map;
        context = c;
        lang = language;

        if(points.size() == 2)
        {
            String url = makeURL(points.get(0).latitude,points.get(0).longitude,points.get(1).latitude,points.get(1).longitude,"driving");
            new connectAsyncTask(url,withIndications).execute();
            return true;
        }
        else if(points.size() > 2)
        {
            String url = makeURL(points,"driving",optimize);
            new connectAsyncTask(url,withIndications).execute();
            return true;
        }

        return false;

    }
private String makeURL (ArrayList<LatLng> points, String mode, boolean optimize){
        StringBuilder urlString = new StringBuilder();

        if(mode == null)
            mode = "driving";

        urlString.append("http://maps.googleapis.com/maps/api/directions/json");
        urlString.append("?origin=");// from
        urlString.append( points.get(0).latitude);
        urlString.append(',');
        urlString.append(points.get(0).longitude);
        urlString.append("&destination=");
        urlString.append(points.get(points.size()-1).latitude);
        urlString.append(',');
        urlString.append(points.get(points.size()-1).longitude);

        urlString.append("&waypoints=");
        if(optimize)
            urlString.append("optimize:true|");
        urlString.append( points.get(1).latitude);
        urlString.append(',');
        urlString.append(points.get(1).longitude);

        for(int i=2;i<points.size()-1;i++)
        {
            urlString.append('|');
            urlString.append( points.get(i).latitude);
            urlString.append(',');
            urlString.append(points.get(i).longitude);
        }


        urlString.append("&sensor=true&mode="+mode);


        return urlString.toString();
    }

    private String makeURL (double sourcelat, double sourcelog, double destlat, double destlog,String mode){
        StringBuilder urlString = new StringBuilder();

        if(mode == null)
            mode = "driving";

        urlString.append("http://maps.googleapis.com/maps/api/directions/json");
        urlString.append("?origin=");// from
        urlString.append(Double.toString(sourcelat));
        urlString.append(",");
        urlString
                .append(Double.toString( sourcelog));
        urlString.append("&destination=");// to
        urlString
                .append(Double.toString( destlat));
        urlString.append(",");
        urlString.append(Double.toString( destlog));
        urlString.append("&sensor=false&mode="+mode+"&alternatives=true&language="+lang);
        return urlString.toString();
    }




    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;
    }




    private class connectAsyncTask extends AsyncTask<Void, Void, String>{
        private ProgressDialog progressDialog;
        String url;
        boolean steps;
        connectAsyncTask(String urlPass, boolean withSteps){
            url = urlPass;
            steps = withSteps;

        }
        @Override
        protected void onPreExecute() {
            // TODO Auto-generated method stub
            super.onPreExecute();
            progressDialog = new ProgressDialog(context);
            progressDialog.setMessage("Fetching route, Please wait...");
            progressDialog.setIndeterminate(true);
            progressDialog.show();
        }
        @Override
        protected String doInBackground(Void... params) {
            JSONParser jParser = new JSONParser();
            String json = jParser.getJSONFromUrl(url);
            return json;
        }
        @Override
        protected void onPostExecute(String result) {
            super.onPostExecute(result);
            progressDialog.hide();
            if(result!=null){

                driverdata.extrastmt = result;

                drawPath(result, steps);
                //makeT(result);


            }else{
                driverdata.extrastmt="null";
            }
        }
    }
    private void drawPath(String  result, boolean withSteps) {

        try {
            //Tranform the string into a json object
            final JSONObject json = new JSONObject(result);
            JSONArray routeArray = json.getJSONArray("routes");
            JSONObject routes = routeArray.getJSONObject(0);
            JSONObject overviewPolylines = routes.getJSONObject("overview_polyline");
            String encodedString = overviewPolylines.getString("points");
            List<LatLng> list = decodePoly(encodedString);

            for(int z = 0; z<list.size()-1;z++){
                LatLng src= list.get(z);
                LatLng dest= list.get(z+1);
                Polyline line = mMap.addPolyline(new PolylineOptions()
                        .add(new LatLng(src.latitude, src.longitude), new LatLng(dest.latitude, dest.longitude))
                        .width(4)
                        .color(Color.BLUE).geodesic(true));
            }


            if(withSteps)
            {
                JSONArray arrayLegs = routes.getJSONArray("legs");
                JSONObject legs = arrayLegs.getJSONObject(0);
                JSONArray stepsArray = legs.getJSONArray("steps");
                //put initial point

                for(int i=0;i<stepsArray.length();i++)
                {
                    Step step = new Step(stepsArray.getJSONObject(i));
                    mMap.addMarker(new MarkerOptions()
                            .position(step.location)
                            .title(step.distance)
                            .snippet(step.instructions)
                            .icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_AZURE)));

                }
            }

        }
        catch (JSONException e) {

        }
    }


    /**
     * Class that represent every step of the directions. It store distance, location and instructions
     */
    private class Step
    {
        public String distance;
        public LatLng location;
        public String instructions;

        Step(JSONObject stepJSON)
        {
            JSONObject startLocation;
            try {

                distance = stepJSON.getJSONObject("distance").getString("text");
                startLocation = stepJSON.getJSONObject("start_location");
                location = new LatLng(startLocation.getDouble("lat"),startLocation.getDouble("lng"));
                try {
                    instructions = URLDecoder.decode(Html.fromHtml(stepJSON.getString("html_instructions")).toString(), "UTF-8");
                } catch (UnsupportedEncodingException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                };

            } catch (JSONException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }

}

public class JSONParser {

    static InputStream is = null;
    static JSONObject jObj = null;
    static String json = "";
    // constructor
    public JSONParser() {
    }
    public String getJSONFromUrl(String url) {

        // Making HTTP request
        try {

            URL urlnew = new URL(url);
            HttpURLConnection urlConnection = (HttpURLConnection) urlnew.openConnection();
            is = new BufferedInputStream(urlConnection.getInputStream());


        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                    is, "iso-8859-1"), 8);
            StringBuilder sb = new StringBuilder();
            String line = null;
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }

            json = sb.toString();
            is.close();
        } catch (Exception e) {
            Log.e("Buffer Error", "Error converting result " + e.toString());
        }
        Log.d("JSON_RUTA", json);
        return json;

    }
}