Question

我对这个主题做了很多研究，但找不到合适的解决方案。我只是有一个api，其中包括学校名称及其纬度，经度。

[  
   {  
      "id":1,
      "name":"Little Angels Higher Secondary School",
      "latitude":27.6514,
      "longitude":85.3359
   },
   {  
      "id":6,
      "name":"Baltimore Secondary School",
      "latitude":27.6514,
      "longitude":85.3359
   }
]

我解析了这个api数据。使用GPStracker类我在我当前位置的谷歌地图上成功添加了一个标记。现在我想在谷歌地图中的所有学校位置添加一个标记，以便我可以知道最近的学校到我曾经打开谷歌地图。这就是我所做的一切，它如何显示空指针异常。

   package com.example.user.educationhunt.fragment;

import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.location.Location;
import android.location.LocationManager;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.Bundle;

import android.support.v4.app.Fragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.Button;
import android.widget.ListView;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.Toast;

import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.VolleyLog;
import com.android.volley.toolbox.JsonArrayRequest;
import com.example.user.educationhunt.R;

import com.example.user.educationhunt.SchoolDetails;
import com.example.user.educationhunt.adapter.CustomListAdapter;
import com.example.user.educationhunt.pojos.AppController;
import com.example.user.educationhunt.pojos.FeeClass;
import com.example.user.educationhunt.pojos.GpsLocation;
import com.example.user.educationhunt.pojos.MySchool;
import com.example.user.educationhunt.pojos.OurSchool;
import com.google.android.gms.location.LocationListener;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.MapView;
import com.google.android.gms.maps.MapsInitializer;
import com.google.android.gms.maps.OnMapReadyCallback;
import com.google.android.gms.maps.model.CameraPosition;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.Marker;
import com.google.android.gms.maps.model.MarkerOptions;

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

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

/**
 * A simple {@link Fragment} subclass.
 */
public class NearMe extends Fragment {
    MapView mMapView;
    private GoogleMap googleMap;
    GpsLocation gpsLocation;
    double longitude, latitude;
    private ProgressDialog pDialog;
    private RadioButton radioSexButton;
    ArrayList al = new ArrayList();
    MySchool mySchool;
    Marker place;
    LatLng  current_location ;

    private static final String TAG = NearMe.class.getSimpleName();

    private static final String url = "http://www.myeducationhunt.com/api/v1/schools";

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View v = inflater.inflate(R.layout.fragment_near_me, container, false);

        radioSexButton = (RadioButton) v.findViewById(R.id.radioSchool);

        if (isConnected()) {
            mMapView = (MapView) v.findViewById(R.id.mapView);
            mMapView.onCreate(savedInstanceState);

            mMapView.onResume();

            try {
                MapsInitializer.initialize(getActivity().getApplicationContext());
            } catch (Exception e) {
                e.printStackTrace();
            }

            gpsLocation = new GpsLocation(getContext());


            if (gpsLocation.canGetLocation()) {
                longitude = gpsLocation.getLongitude();
                latitude = gpsLocation.getLatitude();

                Toast.makeText(getContext(), "latitude:" + latitude + "Longitude:" + longitude, Toast.LENGTH_LONG).show();
            }


            pDialog = new ProgressDialog(getContext());
            pDialog.setMessage("Loading…");
            pDialog.show();


            JsonArrayRequest schoolRequest = new JsonArrayRequest(url,
                    new Response.Listener<JSONArray>() {
                        @Override
                        public void onResponse(JSONArray response) {
                            Log.d(TAG, response.toString());
                            hidePDialog();

                            // Parsing json
                            for (int i = 0; i < response.length(); i++) {
                                try {

                                    JSONObject obj = response.getJSONObject(i);
                                    mySchool = new MySchool();

                                    mySchool.setId(""+obj.getInt("id"));
                                    mySchool.setName(""+obj.getString("name"));
                                    mySchool.setLatitude(Double.parseDouble(""+obj.getDouble("latitude")));
                                    mySchool.setLongitude(Double.parseDouble(""+obj.getDouble("longitude")));


                                    al.add(mySchool);
                                } catch (JSONException e) {
                                    e.printStackTrace();
                                }
                            }

                        }
                    }, new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {
                    VolleyLog.d(TAG, "Error: " + error.getMessage());
                    hidePDialog();
                }
            });

            // Adding request to request queue
            AppController.getInstance().addToRequestQueue(schoolRequest);


            mMapView.getMapAsync(new OnMapReadyCallback() {
                @Override
                public void onMapReady(GoogleMap mMap) {
                    googleMap = mMap;

                    LatLng schoollatlng = new LatLng(latitude, longitude);
                    googleMap.addMarker(new MarkerOptions().position(schoollatlng).title("MyLocation"));
                    CameraPosition cameraPosition = new CameraPosition.Builder().target(schoollatlng).zoom(10).build();
                    googleMap.animateCamera(CameraUpdateFactory.newCameraPosition(cameraPosition));

                    LatLng latlng = new LatLng(mySchool.getLatitude(), mySchool.getLongitude());
                    googleMap.addMarker(new MarkerOptions().position(latlng).title(mySchool.getName()));
                    CameraPosition cameraPosition1 = new CameraPosition.Builder().target(latlng).zoom(10).build();
                    googleMap.animateCamera(CameraUpdateFactory.newCameraPosition(cameraPosition1));
                }
            });

        } else {

            Toast.makeText(getContext(), "Please check your internet connection", Toast.LENGTH_LONG).show();
        }

        return v;
    }

    public boolean isConnected() {
        ConnectivityManager connMgr = (ConnectivityManager) getActivity().getSystemService(Activity.CONNECTIVITY_SERVICE);
        NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
        if (networkInfo != null && networkInfo.isConnected())
            return true;
        else
            return false;
    }

    private void hidePDialog() {
        if (pDialog != null) {
            pDialog.dismiss();
            pDialog = null;
        }
    }
}

有没有人帮助我？请帮助。谢谢提前

这是MySchool课程

package com.example.user.educationhunt.pojos;

/**
 * Created by user on 12/28/2016.
 */
public class MySchool {

    String id;
    String name;
    double latitude;
    double longitude;

    public String getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public double getLatitude() {
        return latitude;
    }

    public double getLongitude() {
        return longitude;
    }

    public void setId(String id) {
        this.id = id;
    }

    public void setLatitude(double latitude) {
        this.latitude = latitude;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setLongitude(double longitude) {
        this.longitude = longitude;
    }

}

这是我的错误日志

 FATAL EXCEPTION: main
                                                                                Process: com.example.user.educationhunt, PID: 20472
                                                                                java.lang.NullPointerException: Attempt to invoke virtual method 'double com.example.user.educationhunt.pojos.MySchool.getLatitude()' on a null object reference
                                                                                    at com.example.user.educationhunt.fragment.NearMe$3.onMapReady(NearMe.java:159)
                                                                                    at com.google.android.gms.maps.MapView$zza$1.zza(Unknown Source)
                                                                                    at com.google.android.gms.maps.internal.zzt$zza.onTransact(Unknown Source)
                                                                                    at android.os.Binder.transact(Binder.java:387)
                                                                                    at zu.a(:com.google.android.gms.DynamiteModulesB:82)
                                                                                    at maps.ad.t$5.run(Unknown Source)
                                                                                    at android.os.Handler.handleCallback(Handler.java:739)
                                                                                    at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                                    at android.os.Looper.loop(Looper.java:148)
                                                                                    at android.app.ActivityThread.main(ActivityThread.java:7325)
                                                                                    at java.lang.reflect.Method.invoke(Native Method)
                                                                                    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
                                                                                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
12-28 10:06:05.046 20472-21276/com.example.user.educationhunt I/qtaguid: Untagging socket 81

Answer 1

您的学校标记应在Google完成初始化后运行。以下是代码示例。

mMapView.getMapAsync(new OnMapReadyCallback() {
            @Override
            public void onMapReady(GoogleMap mMap) {
                googleMap = mMap;

                LatLng schoollatlng = new LatLng(latitude, longitude);
                googleMap.addMarker(new MarkerOptions().position(schoollatlng).title("MyLocation"));
                CameraPosition cameraPosition = new CameraPosition.Builder().target(schoollatlng).zoom(10).build();
                googleMap.animateCamera(CameraUpdateFactory.newCameraPosition(cameraPosition));

                drawSchoolMarker();
            }
});

在班级

中创建新方法

private void drawSchoolMarker(){

    JsonArrayRequest schoolRequest = new JsonArrayRequest(url,
                new Response.Listener<JSONArray>() {
                    @Override
                    public void onResponse(JSONArray response) {
                        Log.d(TAG, response.toString());
                        hidePDialog();

                        // Parsing json
                        for (int i = 0; i < response.length(); i++) {
                            try {

                                JSONObject obj = response.getJSONObject(i);
                                MySchool school = new MySchool();

                                school.setId(""+obj.getInt("id"));
                                school.setName(""+obj.getString("name"));
                                school.setLatitude(Double.parseDouble(""+obj.getDouble("latitude")));
                                school.setLongitude(Double.parseDouble(""+obj.getDouble("longitude")));


                                al.add(school);
                            } catch (JSONException e) {
                                e.printStackTrace();
                            }
                        }

                        //iterate from arraylist
                        for(MySchool school : al){
                           LatLng latlng = new LatLng(school.getLatitude(), school.getLongitude());
                           googleMap.addMarker(new  MarkerOptions().position(latlng).title(school.getName()));
                        }


                    }
                }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                VolleyLog.d(TAG, "Error: " + error.getMessage());
                hidePDialog();
            }
        });

        // Adding request to request queue
        AppController.getInstance().addToRequestQueue(schoolRequest);
}

我没有测试代码但它应该可以工作。

Answer 2

阅读完所有学校位置之后，请使用您的数组列表

Marker  place;
LatLng  current_location ;
    for(int i = 0; i < al.size(); i++){
        current_location = new LatLng(Double.parseDouble(al.get(i).getLatitude()),Double.parseDouble(al.get(i).getLongitude()));
        place= map.addMarker(new MarkerOptions().position(current_location).title("school name here"));
    }

Answer 3

你应该在行中获得NullPointerException：

 LatLng latlng = new LatLng(ourSchool.latitude, ourSchool.longitude);

因为我们学校指的是Null。您已在ArrayList“al”中添加了所有ourSchool对象，如：al.add(ourSchool)

现在尝试在ArrayList中添加数据后从ArrayList“al”进行迭代。

此外，您的以下代码在从网址获取回复之前运行，而您的“ourSchool”在此之前尚未初始化。

mMapView.getMapAsync(new OnMapReadyCallback() {
                @Override
                public void onMapReady(GoogleMap mMap) {
                    googleMap = mMap;

                    LatLng schoollatlng = new LatLng(latitude, longitude);
                    googleMap.addMarker(new MarkerOptions().position(schoollatlng).title("MyLocation"));
                    CameraPosition cameraPosition = new CameraPosition.Builder().target(schoollatlng).zoom(10).build();
                    googleMap.animateCamera(CameraUpdateFactory.newCameraPosition(cameraPosition));

                    LatLng latlng = new LatLng(ourSchool.latitude, ourSchool.longitude);
                    googleMap.addMarker(new MarkerOptions().position(latlng).title(ourSchool.schoolName));
                    CameraPosition cameraPosition1 = new CameraPosition.Builder().target(latlng).zoom(10).build();
                    googleMap.animateCamera(CameraUpdateFactory.newCameraPosition(cameraPosition1));
                }
            });

OurSchool课程：

class OurSchool{

String id;
String name;
double latitude;
double longitude;


public void setId(String id){
this.id=id;
}

public String getId(){
return id;
}
public void setName(String name){
this.name=name;
}

public String getName(){
return name;
}

public void setLatitude(double latitude){
this.latitute=latitude;
}

public double getLatitude(){
return latitude;
}

public void setLongitude(String longitude){
this.longitude=longitude;
}

public double getLongitude(){
return longitude;
}


}

然后在OurSchool类对象中设置值，如：

 ourSchool.setId(""+obj.getInt("id"));

取代

ourSchool.schoolId = obj.getInt("id");

同样为其他

设置值

在Googlemap

3 个答案: