Question

我尝试构建一个显示路线并绘制它的应用程序，用于计算距离后的行程时间，对于所有点A + B + C + D ...但它显示此错误，我不会知道如何解决。

我正在寻找类似的答案，但对此案没有回应

TAL EXCEPTION: main
                  Process: com.elgeos.wayp.wa, PID: 17963
                  java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
                      at com.elgeos.wayp.wa.PathGoogleMapActivity$ParserTask.onPostExecute(PathGoogleMapActivity.java:139)
                      at com.elgeos.wayp.wa.PathGoogleMapActivity$ParserTask.onPostExecute(PathGoogleMapActivity.java:113)
                      at android.os.AsyncTask.finish(AsyncTask.java:651)
                      at android.os.AsyncTask.-wrap1(AsyncTask.java)
                      at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:668)
                      at android.os.Handler.dispatchMessage(Handler.java:102)
                      at android.os.Looper.loop(Looper.java:148)
                      at android.app.ActivityThread.main(ActivityThread.java:5417)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

下面我附上我的完整java活动，Android Studio告诉我一切正常，但是当我调试应用程序时，应用程序失败

package com.elgeos.wayp.wa;

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.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.util.Log;

import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.OnMapReadyCallback;
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.model.PolylineOptions;

public class PathGoogleMapActivity extends FragmentActivity  implements OnMapReadyCallback {

    private static final LatLng LOWER_MANHATTAN = new LatLng(40.722543,
            -73.998585);
    private static final LatLng BROOKLYN_BRIDGE = new LatLng(40.7057, -73.9964);
    private static final LatLng WALL_STREET = new LatLng(40.7064, -74.0094);

    GoogleMap mMap;
    final String TAG = "PathGoogleMapActivity";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_path_google_map);
        SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
                .findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);




    }

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

        MarkerOptions options = new MarkerOptions();
        options.position(LOWER_MANHATTAN);
        options.position(BROOKLYN_BRIDGE);
        options.position(WALL_STREET);
        mMap.addMarker(options);
        String url = getMapsApiDirectionsUrl();
        ReadTask downloadTask = new ReadTask();
        downloadTask.execute(url);

        mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(BROOKLYN_BRIDGE,
                13));

        addMarkers();
    }

    private String getMapsApiDirectionsUrl() {
        String waypoints = "waypoints=optimize:true|"
                + LOWER_MANHATTAN.latitude + "," + LOWER_MANHATTAN.longitude
                + "|" + "|" + BROOKLYN_BRIDGE.latitude + ","
                + BROOKLYN_BRIDGE.longitude + "|" + WALL_STREET.latitude + ","
                + WALL_STREET.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(BROOKLYN_BRIDGE)
                    .title("First Point"));
            mMap.addMarker(new MarkerOptions().position(LOWER_MANHATTAN)
                    .title("Second Point"));
            mMap.addMarker(new MarkerOptions().position(WALL_STREET)
                    .title("Third Point"));
        }
    }



    private class ReadTask extends AsyncTask<String, Void, String> {
        @Override
        protected String doInBackground(String... url) {
            String data = "";
            try {
                HttpConnection http = new HttpConnection();
                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]);
                PathJSONParser parser = new PathJSONParser();
                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;

            // traversing through routes
            for (int i = 0; i < routes.size(); i++) {
                points = new ArrayList<LatLng>();
                polyLineOptions = new PolylineOptions();
                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);
        }
    }
}

Answer 1

列表＆gt; path = routes.get（i）; 这里，路由为空，并且您尝试获取路径列表的大小为null。所以你得到一个NullPointerException。

错误：尝试调用接口方法＆＃39; int java.util.List.size（）＆＃39;

1 个答案: