我的应用程序应该从数据库（在我的情况下从mySQL中）检索标记的经度和纬度，然后在地图上显示它们。在我尝试从Web检索数据之前，它运行良好。有人可以帮帮我吗？其他代码为here
route_activity.java
package com.example.wibisono.tryhard_1;
import android.location.Criteria;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.GooglePlayServicesUtil;
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.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.HashMap;
import java.util.List;
public class route_activity extends FragmentActivity implements LocationListener {
GoogleMap googleMap;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//show error dialog if GoolglePlayServices not available
if (!isGooglePlayServicesAvailable()) {
finish();
}
setContentView(R.layout.map_route);
SupportMapFragment supportMapFragment =
(SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
googleMap = supportMapFragment.getMap();
googleMap.setMyLocationEnabled(true);
LocationManager locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);
Criteria criteria = new Criteria();
String bestProvider = locationManager.getBestProvider(criteria, true);
Location location = locationManager.getLastKnownLocation(bestProvider);
if (location != null) {
onLocationChanged(location);
}
locationManager.requestLocationUpdates(bestProvider, 20000, 0, this);
new RetrieveTask().execute();
}
// Adding marker on the GoogleMaps
//private void addMarker(LatLng latlng) {
// MarkerOptions markerOptions = new MarkerOptions();
// markerOptions.position(latlng);
// markerOptions.title(latlng.latitude + "," + latlng.longitude);
// googleMap.addMarker(markerOptions);
//}
// Background task to retrieve locations from remote mysql server
private class RetrieveTask extends AsyncTask<Void, Void, String> {
@Override
protected String doInBackground(Void... params) {
String strUrl = "http://nfcworld.web.id/public_html/wibisono/retrieve.php";
URL url = null;
StringBuffer sb = new StringBuffer();
try {
url = new URL(strUrl);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.connect();
InputStream iStream = connection.getInputStream();
BufferedReader reader = new BufferedReader(new InputStreamReader(iStream));
String line = "";
while( (line = reader.readLine()) != null){
sb.append(line);
}
reader.close();
iStream.close();
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return sb.toString();
}
@Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
new ParserTask().execute(result);
}
}
// Background thread to parse the JSON data retrieved from MySQL server
private class ParserTask extends AsyncTask<String, Void, List<HashMap<String, String>>>{
@Override
protected List<HashMap<String,String>> doInBackground(String... params) {
DirectionsJSONParser markerParser = new DirectionsJSONParser();
JSONObject json = null;
try {
json = new JSONObject(params[0]);
} catch (JSONException e) {
e.printStackTrace();
}
List<HashMap<String, String>> markersList = markerParser.parse(json);
return markersList;
}
@Override
protected void onPostExecute(List<HashMap<String, String>> result) {
for(int i=0; i<result.size();i++){
HashMap<String, String> marker = result.get(i);
LatLng latlng = new LatLng(Double.parseDouble(marker.get("lat")), Double.parseDouble(marker.get("lng")));
//addMarker(latlng);
}
}
}
@Override
public void onLocationChanged(Location location) {
//TextView locationTv = (TextView) findViewById(R.id.latlongLocation);
double latitude = location.getLatitude();
double longitude = location.getLongitude();
LatLng latLng = new LatLng(latitude, longitude);
//googleMap.addMarker(new MarkerOptions().position(latLng));
googleMap.moveCamera(CameraUpdateFactory.newLatLng(latLng));
googleMap.animateCamera(CameraUpdateFactory.zoomTo(16));
//locationTv.setText("Latitude:" + latitude + ", Longitude:" + longitude);
}
@Override
public void onProviderDisabled(String provider) {
// TODO Auto-generated method stub
}
@Override
public void onProviderEnabled(String provider) {
// TODO Auto-generated method stub
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
// TODO Auto-generated method stub
}
private boolean isGooglePlayServicesAvailable() {
int status = GooglePlayServicesUtil.isGooglePlayServicesAvailable(this);
if (ConnectionResult.SUCCESS == status) {
return true;
} else {
GooglePlayServicesUtil.getErrorDialog(status, this, 0).show();
return false;
}
}
}
这些是我得到的错误
11-11 00:29:55.443 2008-2482/com.example.wibisono.tryhard_1 E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #2
Process: com.example.wibisono.tryhard_1, PID: 2008
java.lang.RuntimeException: An error occured while executing doInBackground()
at android.os.AsyncTask$3.done(AsyncTask.java:304)
at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
at java.util.concurrent.FutureTask.run(FutureTask.java:242)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
at java.lang.Thread.run(Thread.java:818)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'org.json.JSONArray org.json.JSONObject.getJSONArray(java.lang.String)' on a null object reference
at com.example.wibisono.tryhard_1.DirectionsJSONParser.parse(DirectionsJSONParser.java:23)
at com.example.wibisono.tryhard_1.route_activity$ParserTask.doInBackground(route_activity.java:116)
at com.example.wibisono.tryhard_1.route_activity$ParserTask.doInBackground(route_activity.java:106)
at android.os.AsyncTask$2.call(AsyncTask.java:292)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
at java.lang.Thread.run(Thread.java:818)