使用JSON for Android Maps API显示标记

Question

首先，我想提一下，我是Android Studio编程的初学者。

我正在尝试从服务器检索JSON响应，解析它并将标记添加到我的地图中。我有一张工作地图，但标记没有显示出来。任何想法我该怎么办？

这是我的课程

    import android.Manifest;
    import android.content.pm.PackageManager;

import android.location.Location;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.support.v4.content.ContextCompat;
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.SupportMapFragment;
import com.google.android.gms.maps.model.BitmapDescriptorFactory;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;

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

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

public class MapsActivity extends FragmentActivity{

    private GoogleMap map;

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


    }

    @Override
    protected void onResume() {
        super.onResume();
        setUpMapIfNeeded();
        new MarkerTask().execute();
    }

    private void setUpMapIfNeeded() {
        if (map == null) {
            // Try to obtain the map from the SupportMapFragment.
            map = ((SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map))
                    .getMap();
            if (ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION)
                    == PackageManager.PERMISSION_GRANTED) {
                map.setMyLocationEnabled(true);
            } else {
                Toast.makeText(MapsActivity.this, "You have to accept to enjoy all app's services!", Toast.LENGTH_LONG).show();
                if (ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION)
                        == PackageManager.PERMISSION_GRANTED) {
                    map.setMyLocationEnabled(true);
                }
            }

            if (map != null) {


                map.setOnMyLocationChangeListener(new GoogleMap.OnMyLocationChangeListener() {

                    @Override
                    public void onMyLocationChange(Location arg0) {


                        CameraUpdate center = CameraUpdateFactory.newLatLng(new LatLng(arg0.getLatitude(), arg0.getLongitude()));
                        CameraUpdate zoom = CameraUpdateFactory.zoomTo(16);

                        map.moveCamera(center);
                        map.animateCamera(zoom);

                    }
                });

            }
        }
    }
    //--------------------------------------------------------------
        class MarkerTask extends AsyncTask<Void, Void, String> {

        private static final String LOG_TAG = "ExampleApp";

        private static final String SERVICE_URL = "http://(some IP address )/stations.php";


        @Override
        protected String doInBackground(Void... args) {

            HttpURLConnection conn = null;
            final StringBuilder json = new StringBuilder();
            try {

                URL url = new URL(SERVICE_URL);
                conn = (HttpURLConnection) url.openConnection();
                InputStreamReader in = new InputStreamReader(conn.getInputStream());


                int read;
                char[] buff = new char[1024];
                while ((read = in.read(buff)) != -1) {
                    json.append(buff, 0, read);
                }
            } catch (IOException e) {
                Log.e(LOG_TAG, "Error connecting to service", e);
                //throw new IOException("Error connecting to service", e); //uncaught
            } finally {
                if (conn != null) {
                    conn.disconnect();
                }
            }

            return json.toString();
        }


        @Override
        protected void onPostExecute(String json) {

            try {

                JSONArray jsonArray = new JSONArray(json);
                for (int i = 0; i < jsonArray.length(); i++) {
                    JSONObject jsonObj = jsonArray.getJSONObject(i);

                    LatLng latLng = new LatLng(jsonObj.getDouble("lat"),
                            jsonObj.getDouble("lng"));




                    map.addMarker(new MarkerOptions()
                            .icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_BLUE))
                            .title(jsonObj.getString("nume"))
                            .position(latLng));
                }
            } catch (JSONException e) {
                Log.e(LOG_TAG, "Error processing JSON", e);
            }

        }
    }}