我正在开展一个项目，其中当前纬度和经度来自另一个班级。当我关闭手机或第二天打开应用程序时，当前纬度和经度显示为0.0，这是因为位置对象变为空。但是只要我再次打开应用程序，地图就会正确显示。
主类中的代码：
public void getcurrentlocation()
{
gps=new GPSTracker(MainActivity.this);
if(gps.canGetLocation())
{
current_latitude=gps.getLatitude();
current_longitude=gps.getLongitude();
placemarkersonmap();
}
else
{
gps.showSettingsAlert();
}
}
public void placemarkersonmap()
{
googleMap.setMyLocationEnabled(true);
googleMap.getUiSettings().setMyLocationButtonEnabled(true);
LatLng latLng = new LatLng(current_latitude, current_longitude);
Toast.makeText(getApplicationContext(),current_latitude+" "+current_longitude,Toast.LENGTH_LONG).show();
googleMap.moveCamera(CameraUpdateFactory.newLatLngZoom(latLng, 12f));
googleMap.animateCamera(CameraUpdateFactory.newLatLngZoom(latLng, 12f));
MarkerOptions marker = new MarkerOptions().position(new LatLng(8.505439, 76.971293));
googleMap.addMarker(marker);
}
用于检索当前纬度和经度的助手类，GPSTracker类：
package com.example.marinamapseg;
import android.app.AlertDialog;
import android.app.Service;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;
import android.os.IBinder;
import android.provider.Settings;
import android.util.Log;
import android.widget.Toast;
public class GPSTracker extends Service implements LocationListener {
private final Context mContext;
// flag for GPS status
boolean isGPSEnabled = false;
// flag for network status
boolean isNetworkEnabled = false;
// flag for GPS status
boolean canGetLocation = false;
Location location; // location
double latitude; // latitude
double longitude; // 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);
// getting GPS status
isGPSEnabled = locationManager
.isProviderEnabled(LocationManager.GPS_PROVIDER);
// getting network status
isNetworkEnabled = locationManager
.isProviderEnabled(LocationManager.NETWORK_PROVIDER);
if (!isGPSEnabled && !isNetworkEnabled) {
Toast.makeText(getApplicationContext(),"NO PROVIDER ENABLED",Toast.LENGTH_LONG).show();
} else {
this.canGetLocation = true;
// First get location from Network Provider
if (isNetworkEnabled) {
locationManager.requestLocationUpdates(
LocationManager.NETWORK_PROVIDER,
0,
0, this);
Log.d("Network", "Network");
if (locationManager != null) {
location = locationManager
.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
if (location != null) {
latitude = location.getLatitude();
longitude = location.getLongitude();
}
}
}
// if GPS Enabled get lat/long using GPS Services
if (isGPSEnabled) {
if (location == null) {
locationManager.requestLocationUpdates(
LocationManager.GPS_PROVIDER,
0,
0, this);
Log.d("GPS Enabled", "GPS Enabled");
if (locationManager != null) {
location = locationManager
.getLastKnownLocation(LocationManager.GPS_PROVIDER);
if (location != null) {
latitude = location.getLatitude();
longitude = location.getLongitude();
}
}
}
}
}
} catch (Exception e) {
e.printStackTrace();
}
return location;
}
/**
* Stop using GPS listener
* Calling this function will stop using GPS in your app
* */
public void stopUsingGPS(){
if(locationManager != null){
locationManager.removeUpdates(GPSTracker.this);
}
}
/**
* Function to get latitude
* */
public double getLatitude(){
if(location != null){
latitude = location.getLatitude();
}
// return latitude
return latitude;
}
/**
* Function to get longitude
* */
public double getLongitude(){
if(location != null){
longitude = location.getLongitude();
}
// return longitude
return longitude;
}
/**
* Function to check GPS/wifi enabled
* @return boolean
* */
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) {
}
@Override
public void onProviderDisabled(String provider) {
}
@Override
public void onProviderEnabled(String provider) {
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}
@Override
public IBinder onBind(Intent arg0) {
return null;
}
}
我尝试将更新之间的最短时间和更新之间的最小距离设置为requestLocationUpdates locationmanager方法的0。但这也没有帮助。
所以问题是为什么当我第二天打开应用程序时，location对象返回null。一旦关闭应用程序并再次重新启动它也会正常工作。请帮助！
答案 0 :(得分：0)
要获取更新，请使用您已实施的LocationListener界面，而不是使用
if (locationManager != null) {
location = locationManager
.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
if (location != null) {
latitude = location.getLatitude();
longitude = location.getLongitude();
}
}
在onLocationChanged()
@Override
public void onLocationChanged(Location location) {
latitude = location.getLatitude();
longitude = location.getLongitude();
}
这可确保当新的位置更新可用时，它将存储在您的相应变量中。
PS：要在后台获取位置更新，请确保在关闭应用时不会终止您的服务。如果您想要在重新启动手机时保留更改，也可以使用SharedPreferences。