3点Android Google Maps API2之间的地图路线

Question

请帮帮我）我想写3点之间的地图路由。 我有这段代码，但是有一个问题：

E / AndroidRuntime致命错误：主进程：com.example.max.mymaprouting，PID：7236 java.lang.NullPointerException：尝试在null对象引用上调用接口方法'int java.util.List.size（）' com.example.max.mymaprouting.MapsActivity $ ParserTask.onPostExecute（MapsActivity.java:104）上的com.example.max.mymaprouting.MapsActivity $ ParserTask.onPostExecute（MapsActivity.java:131）在android.os.AsyncTask.finish（ android.os.AsyncTask.access $ 500（AsyncTask.java:177）的android.os.AsyncTask $ InternalHandler.handleMessage（AsyncTask.java:653）的android.os.Handler.dispatchMessage（Handler）的AsyncTask.java:636）。 java.102中的android.os.Looper.loop（Looper.java:135）在java.lang.reflect.Method.invoke（本机方法）处android.app.ActivityThread.main（ActivityThread.java:5254） com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:903）上的.lang.reflect.Method.invoke（Method.java:372）com.android.internal.os.ZygoteInit.main（ZygoteInit .java：698）

即：

for (int i = 0; i < routes.size(); i++) {
                List<HashMap<String, String>> path = routes.get(i);

MapsActivity和其他Java代码段（实现了所有所需的导入）：

import android.support.v4.app.FragmentActivity;
import android.os.Bundle;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.model.PolylineOptions;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

import org.json.JSONObject;

import android.graphics.Color;
import android.os.AsyncTask;
import android.util.Log;



public class MapsActivity extends FragmentActivity {

    private GoogleMap mMap;

    private static final LatLng HOME = new LatLng(52.448720, 35.451194);
    private static final LatLng OFFICE = new LatLng(45.516205, 30.436827);
    private static final LatLng RANDOM = new LatLng(45.510144, 31.451873);



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

        SupportMapFragment fragment = (SupportMapFragment) getSupportFragmentManager()
                .findFragmentById(R.id.map);
        mMap = fragment.getMap();
        mMap.setMyLocationEnabled(true);
        MarkerOptions options = new MarkerOptions();
        options.position(HOME);
        options.position(OFFICE);
        options.position(RANDOM);
        mMap.addMarker(options);
        String url = getMapsApiDirectionsUrl();
        ReadTask downloadTask = new ReadTask();
        downloadTask.execute(url);

               addMarkers();

    }

    private String getMapsApiDirectionsUrl() {
        String waypoints = "waypoints=optimize:true|"
                + HOME.latitude + "," + HOME.longitude
                + "|" + "|" + OFFICE.latitude + ","
                + OFFICE.longitude + "|" + RANDOM.latitude + ","
                + RANDOM.longitude;

        String sensor = "sensor=false";
        String params = waypoints + "&" + sensor;
        String output = "json";
        String url = "https://maps.googleapis.com/maps/api/directions/"+ output + "?" + params;
        return url;
    }
    private void addMarkers() {
        if (mMap != null) {
            mMap.addMarker(new MarkerOptions().position(OFFICE)
                    .title("Office"));
            mMap.addMarker(new MarkerOptions().position(HOME)
                    .title("home, sweet home"));
            mMap.addMarker(new MarkerOptions().position(RANDOM)
                    .title("Random point"));
        }
    }
    private class ReadTask extends AsyncTask<String, Void, String> {
        @Override
        protected String doInBackground(String... url) {
            String data = "";
            try {
                Http http = new Http();
                data = http.readUrl(url[0]);
            } catch (Exception e) {
                Log.d("Background Task", e.toString());
            }
            return data;
        }




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

        }
    }

    private class ParserTask extends AsyncTask<String, Integer, List<List<HashMap<String, String>>>> {

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


        @Override
        protected void onPostExecute(List<List<HashMap<String, String>>> routes) {
           // ArrayList<LatLng> points = null;
            PolylineOptions polyLineOptions = null;
            ArrayList<LatLng> points = new ArrayList<LatLng>();
            polyLineOptions = new PolylineOptions();


                for (int i = 0; i < routes.size(); i++) {
                    List<HashMap<String, String>> path = routes.get(i);

                    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);


                    polyLineOptions.addAll(points);
                    polyLineOptions.width(2);
                    polyLineOptions.color(Color.BLUE);
                }
            }


            mMap.addPolyline(polyLineOptions);
        }
    }
}

HTTP

import java.net.HttpURLConnection;
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.IOException;
import java.net.URL;

import android.util.Log;

    public class Http {
    public String readUrl(String mapsApiUrl) throws IOException {
        String data = "";
        InputStream iStream = null;
        HttpURLConnection urlConnection = null;
        try {
            URL url = new URL(mapsApiUrl);
            urlConnection = (HttpURLConnection) url.openConnection();
            urlConnection.connect();
            iStream = urlConnection.getInputStream();
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                    iStream));
            StringBuffer buffer = new StringBuffer();
            String line = "";
            while ((line = reader.readLine()) != null) {
                buffer.append(line);
            }
            data = buffer.toString();
            reader.close();
        } catch (Exception e) {
           // Log.d("Exception while reading url", e.toString());
        } finally {
            iStream.close();
            urlConnection.disconnect();
        }
        return data;
    }}

JSONParser

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import com.google.android.gms.maps.model.LatLng;
    public class JSONParser {

    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");

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

                for (int j = 0; j < jLegs.length(); j++) {
                    jSteps = ((JSONObject) jLegs.get(j)).getJSONArray("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);


                        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;
    }


    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;
    }}

如何解决？ 谢谢。

Answer 1

在第131行，您的路线可能为空。 您应先进行空指针异常检查，然后再进行逻辑处理。

if (routes != null) {
  // do your stuffs
}