Android-获取当前位置但经纬度返回0.0(计算错误)

Question

我正在尝试制作一个简单的程序来执行将显示在 ListView 中的距离计算。我使用 androidhive 中的 GPSTracker，并为我的列表 Activity 调用纬度和经度

public class GPSTracker extends Service implements LocationListener {

private final Context mContext;
boolean isGPSEnabled =false;
boolean isNetworkEnabled = false;
boolean canGetLocation = false;
Location location;
double latitude;
double longitude;

// The minimum distance to change Updates in meters
private static final long MIN_DISTANCE_CHANGE_FOR_UPDATES = 10; // 10 meters

// The minimum time between updates in milliseconds
private static final long MIN_TIME_BW_UPDATES = 1000 * 60 * 1; // 1 minute

// Declaring a Location Manager
protected LocationManager locationManager;

public GPSTracker(Context context){
    this.mContext = context;
    getLocation();
}

public Location getLocation() {
    try{
        locationManager = (LocationManager) mContext.getSystemService(LOCATION_SERVICE);
        isGPSEnabled = locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER);
        if(!isGPSEnabled&& !isNetworkEnabled){
            //no network enable
        }else {
            this.canGetLocation = true;
            if(isNetworkEnabled){
                locationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, MIN_TIME_BW_UPDATES, MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
                Log.d("Network","Network");
                if(locationManager != null){
                    location = locationManager.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);

                    if(location != null){
                        latitude = location.getLatitude();
                        longitude = location.getLongitude();
                    }
                }
            }

            if(isGPSEnabled){
                if(location == null){
                    locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, MIN_TIME_BW_UPDATES, MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
                    if(location != null){
                        latitude = location.getLatitude();
                        longitude = location.getLongitude();
                    }
                }
            }
        }

    } catch (Exception e){
        e.printStackTrace();
    }
    return location;        
} 

public void stopUsingGPS(){
    if(locationManager != null){
        locationManager.removeUpdates(GPSTracker.this);

    }
}

public double getLatitude(){
    if(location != null){
        latitude = location.getLatitude();
    }
    return latitude;
}

public double getLongitude(){
    if(location != null){
        longitude = location.getLongitude();

    }
    return longitude;
}

public boolean canGetLocation(){
    return this.canGetLocation;
}


 /**
 * Function to show settings alert dialog
 * On pressing Settings button will lauch Settings Options
 * */
public void showSettingsAlert(){
    AlertDialog.Builder alertDialog = new AlertDialog.Builder(mContext);

    // Setting Dialog Title
    alertDialog.setTitle("GPS is settings");

    // Setting Dialog Message
    alertDialog.setMessage("GPS is not enabled. Do you want to go to settings menu?");

    // On pressing Settings button
    alertDialog.setPositiveButton("Settings", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog,int which) {
            Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
            mContext.startActivity(intent);
        }
    });

    // on pressing cancel button
    alertDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int which) {
        dialog.cancel();
        }
    });

    // Showing Alert Message
    alertDialog.show();
}



@Override
public void onLocationChanged(Location location) {
    // TODO Auto-generated method stub

}

@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

}

@Override
public IBinder onBind(Intent intent) {
    // TODO Auto-generated method stub
    return null;
}
}

还有我的列表 Activity

public class Mobil extends ListFragment implements LocationListener{
GPSTracker gps;
private static final String url = "http://10.0.2.2/tambalban/car.php";  

JSONArray tambalban = null;
ArrayList<HashMap<String, String>> listMobil = new ArrayList<HashMap<String, String>>();
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);             
    new getJSONData().execute();        
}

public class getJSONData extends
        AsyncTask<String, Integer, ArrayList<HashMap<String, String>>> {

    @Override
    protected ArrayList<HashMap<String, String>> doInBackground(
            String... params) {

        JSONParser jParser = new JSONParser();
        JSONObject json = jParser.getJSONFromURL(url);

        gps = new GPSTracker(getActivity()); // is it right calling from GPSTracker?    
        double lat_user = gps.getLatitude(); // get latitude, right?
        double lng_user = gps.getLongitude();
        System.out.println("lat_user : "+lat_user+""); // print in logcat return 0.00
        System.out.println("lng_user : "+lng_user+"");// print in logcat return 0.00    

        try {
            tambalban = json.getJSONArray(TAG_TAMBALBAN);

            for (int i = 0; i < tambalban.length(); i++) {
                JSONObject mtr = tambalban.getJSONObject(i);

                 String id_tb = mtr.getString(TAG_ID);
                 String name_tb = mtr.getString(TAG_NAMA);
                 String address_tb = mtr.getString(TAG_ALAMAT);
                 String telp_tb = mtr.getString(TAG_TELP);
                 String lat = mtr.getString(TAG_LAT);
                 String lng = mtr.getString(TAG_LNG);

                 double lat_tujuan = Double.parseDouble(lat);
                 double lng_tujuan = Double.parseDouble(lng);
                         double distance = hitungJarak(lat_user, lng_user, lat_tujuan, lng_tujuan);
                 distance = RoundDecimal(distance, 2);
                 String dist = Double.toString(distance)+" km";

                 HashMap<String, String> a = new HashMap<String, String>();

                a.put(TAG_ID, id_tb);
                a.put(TAG_NAMA, name_tb);
                a.put(TAG_ALAMAT, address_tb);
                a.put(TAG_TELP, telp_tb);
                a.put(TAG_LAT, lat);
                a.put(TAG_LNG, lng);
                a.put(TAG_JARAK, dist);

                listMobil.add(a);                       
            }

        } catch (JSONException e) {
            e.printStackTrace();
        }
        return listMobil;

    }

private double RoundDecimal(double distance, int i) {
        BigDecimal bd = new BigDecimal(distance);
        bd = bd.setScale(i, 6);         
        return bd.doubleValue();
    }


private double hitungJarak(double lat_user, double lng_user,
            double lat_tujuan, double lng_tujuan) {
    double dist;
    double radius = 6371;
    double dLat = Math.toRadians(lat_tujuan - lat_user);
    double dLon = Math.toRadians(lng_tujuan- lng_user);
    double a = Math.sin(dLat/2) * Math.sin(dLat /2)
            + Math.cos(Math.toRadians(lat_user)) * Math.cos(Math.toRadians(lat_tujuan)) 
            * Math.sin(dLon/ 2) * Math.sin(dLon/2);

    double c = 2 * Math.asin(Math.sqrt(a));
    double valueResult = radius * c;
    double km = valueResult/1;
    DecimalFormat newFormat = new DecimalFormat("####");
    int kmInDec = Integer.valueOf(newFormat.format(km));

    dist = radius * c;

        return dist;
    }


    @Override
    protected void onPostExecute(
            ArrayList<HashMap<String, String>> listMobil) {
        // TODO Auto-generated method stub
        super.onPostExecute(listMobil);
        ListAdapter adapter = new SimpleAdapter(getActivity(), listMobil,
                R.layout.list_item, new String[] { TAG_NAMA, TAG_ALAMAT, TAG_JARAK },
                new int[] { R.id.namatb, R.id.alamattb,R.id.jarak });
        setListAdapter(adapter);        
    }

}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    return inflater.inflate(R.layout.list_fragment, container, false);
}

@Override
public void onListItemClick(ListView l, View v, int position, long id) {
    // TODO Auto-generated method stub

    super.onListItemClick(l, v, position, id);
    String pilih = getListAdapter().getItem(position).toString();
    Toast.makeText(getActivity(),
            pilih,
            Toast.LENGTH_LONG).show();



    Intent i = new Intent(getActivity(), DetailDaftar.class);
    Bundle bundle = new Bundle();
    bundle.putString("Selected", pilih);


    i.putExtras(bundle);
    startActivity(i); 
}

@Override
public void onLocationChanged(Location location) {
    // TODO Auto-generated method stub

}

@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

}   
}

我使用 Sytem.out.println 检查，纬度和经度都返回 0.00。我调用当前位置错了吗？感谢您的帮助。

Answer 1

您应该在 AsyncTask 之外创建您的 GPSTracker gps 对象，尝试像这样:

 @Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);    
gps = new GPSTracker(getActivity()); // is it right calling from GPSTracker?             
new getJSONData().execute();        

并且还将所需的权限添加到您的manifest.xml文件中:

<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" /> 
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />