我正在尝试从API获取JSON对象，以便在Google地图上为每个标记使用Lat Long。
我可以读取JSON，因为我已经能够将它作为字符串放在listview中，但是cants似乎将它解析为double，它每次都会崩溃。
爪哇：
package com.fly.plane;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import com.fly.plane.R;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.MapFragment;
import com.google.android.gms.maps.Projection;
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.Marker;
import com.google.android.gms.maps.model.MarkerOptions;
import android.R.array;
import android.app.ListActivity;
import android.app.ProgressDialog;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Point;
import android.location.Location;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Handler;
import android.os.SystemClock;
import android.support.v4.app.FragmentActivity;
import android.util.Log;
import android.view.View;
import android.view.animation.Interpolator;
import android.view.animation.LinearInterpolator;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
public class MyMapActivity extends ListActivity {
private ProgressDialog pDialog;
// URL to get data JSON
private static String url = "http://edmundgentle.com/snippets/flights/api.php";
// JSON Node speeds
private static final String TAG_data = "data";
private static final String TAG_BEARING = "bearing";
private static final String TAG_speed = "speed";
private static final String TAG_ARR = "arr";
private static final String TAG_DEP = "dep";
private static final String TAG_DEP_LAT = "lat";
private static final String TAG_DEP_LON = "lon";
// data JSONArray
JSONArray data = null;
// Hashmap for ListView
ArrayList<HashMap<String, String>> contactList;
// Hashmap for ListView
ArrayList<Double> ct;
//final Handler handler;
private GoogleMap mMap;
public static final LatLng dest(int i){
final double latitude = -34.6 * i;
final double longitude = 34.23 * i;
return new LatLng(latitude, longitude);
}
public double latt = -15.48169437461;
public double lng = -15.48169437461;
public ArrayList<Integer> dLat;
public String dlat;
public String dlon;
public String alat;
public String alon;
public boolean wait = true;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_my_map);
contactList = new ArrayList<HashMap<String, String>>();
ct = new ArrayList<Double>();
//ListView lv = getListView();
//create markers
new Getdata().execute();
}
}
/**
* Async task class to get json by making HTTP call
* */
private class Getdata extends AsyncTask<Void, Void, Void> {
@Override
protected void onPreExecute() {
super.onPreExecute();
// Showing progress dialog
pDialog = new ProgressDialog(MyMapActivity.this);
pDialog.setMessage("Please wait...");
pDialog.setCancelable(false);
pDialog.show();
}
@Override
protected Void doInBackground(Void... arg0) {
// Creating service handler class instance
HTTPHandler sh = new HTTPHandler();
// Making a request to url and getting response
String jsonStr = sh.makeServiceCall(url, HTTPHandler.GET);
Log.d("Response: ", "> " + jsonStr);
boolean limit = false;
int j = 0;
if (jsonStr != null || limit == false) {
j++;
//if (j > 20)limit = true;
try {
JSONObject jsonObj = new JSONObject(jsonStr);
// Getting JSON Array node
data = jsonObj.getJSONArray(TAG_data);
// looping through All data
for (int i = 0; i < data.length(); i++) {
JSONObject c = data.getJSONObject(i);
// departure node is JSON Object
JSONObject dep = c.getJSONObject(TAG_DEP);
//String dtime = dep.getString(TAG_DEP_TIME);
String dlat = dep.getString(TAG_DEP_LAT);
String dlon = dep.getString(TAG_DEP_LON);
// arrival node is JSON Object
JSONObject arr = c.getJSONObject(TAG_ARR);
// tmp hashmap for single contact
HashMap<String, String> contact = new HashMap<String, String>();
contact.put(TAG_DEP_LAT, dlat );
contact.put(TAG_DEP_LON,dlon);
// adding contact to contact list
contactList.add(contact);
if (i== data.length()){
wait = false;
}
}
} catch (JSONException e) {
e.printStackTrace();
}
} else {
Log.e("ServiceHandler", "Couldn't get any data from the url");
}
return null;
}
@Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
// Dismiss the progress dialog
if (pDialog.isShowing())
pDialog.dismiss();
// use plane api for latlon
mMap = ((MapFragment) getFragmentManager().findFragmentById(R.id.map)).getMap();
List<Marker> markers = new ArrayList<Marker>();
for (int i = 0; i < 1 ; i++)
{
// Now parse it in double
double latitude = Double.parseDouble(dlat);
double longitude = Double.parseDouble(dlon);
//double latitude = 34 + i;
//double longitude = 56 + i;
Marker marker = mMap.addMarker(new MarkerOptions()
.position(new LatLng(latitude, longitude))
//.position(new LatLng(latitude, longitude))
.title("Hello world")
.icon(BitmapDescriptorFactory.fromResource(R.drawable.planemarker)));
markers.add(marker);
}
//setListAdapter(adapter);
}
}
}
以下是我收到的消息：
02-17 14:58:06.635: D/dalvikvm(23289): GC_FOR_ALLOC freed 54K, 24% free 23518K/30936K, paused 24ms, total 24ms
02-17 14:58:06.645: I/dalvikvm-heap(23289): Grow heap (frag case) to 30.616MB for 4194320-byte allocation
02-17 14:58:07.726: D/dalvikvm(23289): GC_FOR_ALLOC freed 4204K, 23% free 23921K/30932K, paused 33ms, total 33ms
02-17 14:58:07.736: I/dalvikvm-heap(23289): Grow heap (frag case) to 31.010MB for 4194320-byte allocation
02-17 14:58:08.517: D/dalvikvm(23289): GC_FOR_ALLOC freed 4293K, 23% free 23831K/30932K, paused 29ms, total 30ms
02-17 14:58:08.527: I/dalvikvm-heap(23289): Grow heap (frag case) to 30.922MB for 4194320-byte allocation
02-17 14:58:09.227: D/dalvikvm(23289): GC_FOR_ALLOC freed 4194K, 23% free 23868K/30932K, paused 27ms, total 27ms
02-17 14:58:09.237: I/dalvikvm-heap(23289): Grow heap (frag case) to 30.958MB for 4194320-byte allocation
02-17 14:58:09.968: D/dalvikvm(23289): GC_FOR_ALLOC freed 4149K, 23% free 23884K/30932K, paused 25ms, total 26ms
02-17 14:58:09.968: I/dalvikvm-heap(23289): Grow heap (frag case) to 30.973MB for 4194320-byte allocation
02-17 14:58:10.118: D/dalvikvm(23289): GC_FOR_ALLOC freed 4377K, 24% free 23626K/30932K, paused 25ms, total 25ms
02-17 14:58:10.128: I/dalvikvm-heap(23289): Grow heap (frag case) to 30.721MB for 4194320-byte allocation
02-17 14:58:10.439: D/dalvikvm(23289): GC_FOR_ALLOC freed 4508K, 24% free 23642K/30932K, paused 24ms, total 25ms
02-17 14:58:13.532: D/dalvikvm(23289): GC_FOR_ALLOC freed 2705K, 24% free 23782K/30932K, paused 26ms, total 27ms
02-17 14:58:25.974: D/dalvikvm(23289): GC_FOR_ALLOC freed 1949K, 20% free 24954K/30932K, paused 37ms, total 38ms
02-17 14:58:32.340: I/dalvikvm(23289): threadid=3: reacting to signal 3
02-17 14:58:32.430: I/dalvikvm(23289): Wrote stack traces to '/data/anr/traces.txt'
02-17 14:58:39.787: D/dalvikvm(23289): GC_FOR_ALLOC freed 1959K, 17% free 26506K/31692K, paused 51ms, total 51ms
02-17 14:58:54.081: D/dalvikvm(23289): GC_FOR_ALLOC freed 2235K, 17% free 28302K/33764K, paused 67ms, total 69ms
02-17 14:59:12.779: D/AndroidRuntime(23289): Shutting down VM
02-17 14:59:12.779: W/dalvikvm(23289): threadid=1: thread exiting with uncaught exception (group=0x41890898)
02-17 14:59:12.829: E/AndroidRuntime(23289): FATAL EXCEPTION: main
02-17 14:59:12.829: E/AndroidRuntime(23289): java.lang.NullPointerException
02-17 14:59:12.829: E/AndroidRuntime(23289): at java.lang.StringToReal.parseDouble(StringToReal.java:244)
02-17 14:59:12.829: E/AndroidRuntime(23289): at java.lang.Double.parseDouble(Double.java:295)
02-17 14:59:12.829: E/AndroidRuntime(23289): at com.fly.plane.MyMapActivity$Getdata.onPostExecute(MyMapActivity.java:222)
02-17 14:59:12.829: E/AndroidRuntime(23289): at com.fly.plane.MyMapActivity$Getdata.onPostExecute(MyMapActivity.java:1)
02-17 14:59:12.829: E/AndroidRuntime(23289): at android.os.AsyncTask.finish(AsyncTask.java:631)
02-17 14:59:12.829: E/AndroidRuntime(23289): at android.os.AsyncTask.access$600(AsyncTask.java:177)
02-17 14:59:12.829: E/AndroidRuntime(23289): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
02-17 14:59:12.829: E/AndroidRuntime(23289): at android.os.Handler.dispatchMessage(Handler.java:99)
02-17 14:59:12.829: E/AndroidRuntime(23289): at android.os.Looper.loop(Looper.java:137)
02-17 14:59:12.829: E/AndroidRuntime(23289): at android.app.ActivityThread.main(ActivityThread.java:5419)
02-17 14:59:12.829: E/AndroidRuntime(23289): at java.lang.reflect.Method.invokeNative(Native Method)
02-17 14:59:12.829: E/AndroidRuntime(23289): at java.lang.reflect.Method.invoke(Method.java:525)
02-17 14:59:12.829: E/AndroidRuntime(23289): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1187)
02-17 14:59:12.829: E/AndroidRuntime(23289): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003)
02-17 14:59:12.829: E/AndroidRuntime(23289): at dalvik.system.NativeStart.main(Native Method)
我想我已经想通了
double latitude = Double.parseDouble(dlat);
double longitude = Double.parseDouble(dlon);
似乎导致问题，就像我将它们更改为设定值一样，它可以正常工作。
任何帮助都会受到赞赏，我已经花了几天时间，并且无法弄清楚它为什么不起作用！
干杯菲尔。
答案 0 :(得分：1)
dlat和dlong字符串。它们与您在代码顶部创建的全局dlat和dlong变量无关。
String dlat = dep.getString(TAG_DEP_LAT);
String dlon = dep.getString(TAG_DEP_LON);
但在onPostExecute内部，您尝试访问您在开头创建的全局变量，但看起来您从未初始化它们。
double latitude = Double.parseDouble(dlat);
double longitude = Double.parseDouble(dlon);
这就是为什么你得到一个nullpointer。
编辑：快速修复 - 尝试替换（在doInBackground方法中）
String dlat = dep.getString(TAG_DEP_LAT);
String dlon = dep.getString(TAG_DEP_LON);
通过
dlat = dep.getString(TAG_DEP_LAT);
dlon = dep.getString(TAG_DEP_LON);