在我的应用程序中想要从数据库显示我的位置，我发现代码这样做，但我得到这个错误所以请帮助我！ ＆＃39;这是我的MainnActivity＆＃39;
package com.ry.rhcomptence.accessiblemaroc;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.view.Menu;
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 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.io.OutputStreamWriter;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.HashMap;
import java.util.List;
public class MainnActivity extends FragmentActivity implements OnMapReadyCallback {
GoogleMap mGoogleMap;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_mainn);
// Getting reference to SupportMapFragment
SupportMapFragment fragment = (SupportMapFragment) getSupportFragmentManager()
.findFragmentById(R.id.map);
// Creating GoogleMap from SupportMapFragment
//mGoogleMap = fragment.getMap();
fragment.getMapAsync(this);
// Setting OnClickEvent listener for the GoogleMap
/**mGoogleMap.setOnMapClickListener(new OnMapClickListener() {
@Override
public void onMapClick(LatLng latlng) {
addMarker(latlng);
sendToServer(latlng);
}
});*/
// Starting locations retrieve task
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);
mGoogleMap.addMarker(markerOptions);
}
// Invoking background thread to store the touched location in Remove MySQL server
private void sendToServer(LatLng latlng) {
new SaveTask().execute(latlng);
}
@Override
public void onMapReady(GoogleMap googleMap) {
// Enabling MyLocation button for the Google Map
/**if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
// TODO: Consider calling
// ActivityCompat#requestPermissions
// here to request the missing permissions, and then overriding
// public void onRequestPermissionsResult(int requestCode, String[] permissions,
// int[] grantResults)
// to handle the case where the user grants the permission. See the documentation
// for ActivityCompat#requestPermissions for more details.
return;
}
mGoogleMap.setMyLocationEnabled(true);*/
}
// Background thread to save the location in remove MySQL server
private class SaveTask extends AsyncTask<LatLng, Void, Void> {
@Override
protected Void doInBackground(LatLng... params) {
String lat = Double.toString(params[0].latitude);
String lng = Double.toString(params[0].longitude);
String strUrl = "https://accessiblemaroc.000webhostapp.com/save.php";
URL url = null;
try {
url = new URL(strUrl);
HttpURLConnection connection = (HttpURLConnection) url
.openConnection();
connection.setRequestMethod("POST");
connection.setDoOutput(true);
OutputStreamWriter outputStreamWriter = new OutputStreamWriter(
connection.getOutputStream());
outputStreamWriter.write("lat=" + lat + "&lng="+lng);
outputStreamWriter.flush();
outputStreamWriter.close();
InputStream iStream = connection.getInputStream();
BufferedReader reader = new BufferedReader(new
InputStreamReader(iStream));
StringBuffer sb = new StringBuffer();
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 null;
}
}
// 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 = "https://accessiblemaroc.000webhostapp.com/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) {
MarkerJSONParser markerParser = new MarkerJSONParser();
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 boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
}
＆＃39;问题在哪里MarkerJSONParser.JAVA：＆＃39;
package com.ry.rhcomptence.accessiblemaroc;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
public class MarkerJSONParser {
/** Receives a JSONObject and returns a list */
public List<HashMap<String,String>> parse(JSONObject jObject){
JSONArray jMarkers =null;
try {
/** Retrieves all the elements in the 'markers' array */
jMarkers = jObject.getJSONArray("markers");
} catch (JSONException e) {
e.printStackTrace();
}
/** Invoking getMarkers with the array of json object
* where each json object represent a marker
*/
return getMarkers(jMarkers);
}
private List<HashMap<String, String>> getMarkers(JSONArray jMarkers){
int markersCount = jMarkers.length();
List<HashMap<String, String>> markersList = new ArrayList<HashMap<String,String>>();
HashMap<String, String> marker = null;
/** Taking each marker, parses and adds to list object */
for(int i=0; i<markersCount;i++){
try {
/** Call getMarker with marker JSON object to parse the marker */
marker = getMarker((JSONObject)jMarkers.get(i));
markersList.add(marker);
}catch (JSONException e){
e.printStackTrace();
}
}
return markersList;
}
/** Parsing the Marker JSON object */
private HashMap<String, String> getMarker(JSONObject jMarker){
HashMap<String, String> marker = new HashMap<String, String>();
String lat = "-NA-";
String lng ="-NA-";
try {
// Extracting latitude, if available
if(!jMarker.isNull("lat")){
lat = jMarker.getString("lat");
}
// Extracting longitude, if available
if(!jMarker.isNull("lng")){
lng = jMarker.getString("lng");
}
marker.put("lat", lat);
marker.put("lng", lng);
} catch (JSONException e) {
e.printStackTrace();
}
return marker;
}
}
＆＃39;最后这是 ERROR ＆＃39;
E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #2
java.lang.RuntimeException: An error occured while executing doInBackground()
at android.os.AsyncTask$3.done(AsyncTask.java:299)
at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
at java.util.concurrent.FutureTask.run(FutureTask.java:137)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
at java.lang.Thread.run(Thread.java:856)
Caused by: java.lang.NullPointerException
at com.ry.rhcomptence.accessiblemaroc.MarkerJSONParser.parse(MarkerJSONParser.java:19)
at com.ry.rhcomptence.accessiblemaroc.MainnActivity$ParserTask.doInBackground(MainnActivity.java:191)
at com.ry.rhcomptence.accessiblemaroc.MainnActivity$ParserTask.doInBackground(MainnActivity.java:181)
at android.os.AsyncTask$2.call(AsyncTask.java:287)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
at java.util.concurrent.FutureTask.run(FutureTask.java:137)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
at java.lang.Thread.run(Thread.java:856)
答案 0 :(得分：0)
您没有尝试在ParserTask中获取数据
rootKey=[Row(key1='value1', key2='value2', key3='value3'), Row(key1='value1', key2='value2', key3='value3'), Row(key1='value1', key2='value2', key3='value3'), Row(key1='value1', key2='value2', key3='value3')]
您提到这是：
>>> df.select('column').show(20, False)
+-----------------------------------------------------------------+
|column |
+-----------------------------------------------------------------+
|[[1,1,1], [1,2,6], [1,2,13], [1,3,3]] |
|[[2,1,1], [2,3,6], [2,4,10]] |
|[[1,1,1], [1,1,6], [1,2,1], [2,2,2], [2,3,6], [1,3,7], [2,4,10]] |
但是你没有从MySQL服务器中检索数据，而这反过来又不会给你什么。当你没有将任何内容传递给MarkerJSONParser并尝试解析任何内容时。这将导致NullPointerException。