当天的问候。我正在开发应用程序，我需要在其中显示地图。 我想在我当前的位置默认显示地图，但我无法这样做。我已经尝试了几种获取当前位置（LatLng）的方法。 我也遵循了这个link，当我从Android设备监视器发送LatLng但在真实设备上失败时，链接在模拟器上工作正常。
并写了一段简单的代码
Location myLoc=mMap.getMyLocation();
double cLat=myLoc.getLatitude();
double cLng=myLoc.getLongitude();
showMap(cLat,cLng);
上面的代码返回NULL。卡住了。请帮忙
答案 0 :(得分：6)
创建一个GpsTracker.java类：
import android.app.AlertDialog;
import android.app.Service;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.location.GpsStatus;
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;
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 = 1000; // 10 meters
// The minimum time between updates in milliseconds
private static final long MIN_TIME_BW_UPDATES = 100000 * 60 * 1; // 5 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) {
// no network provider is enabled
//showSettingsAlert();
} 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 GPS Enabled get lat/long using GPS Services
else {
if(isGPSEnabled) {
if (location == null) {
locationManager.requestLocationUpdates(
LocationManager.GPS_PROVIDER,
MIN_TIME_BW_UPDATES,
MIN_DISTANCE_CHANGE_FOR_UPDATES, 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();
System.exit(0);
}
});
// 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;
}
}
现在您可以获取 GpsTracker.java 的位置创建实例，如：
GPSTracker gpstracker=new GPSTracker(EditProfile.this);
double lat=gpstracker.getLatitude();
double longitude=gpstracker.getLongitude();
此外，您可以检查FusedLocationApi以获取当前的纬度和经度.FusedLocationApi比以前的方法消耗的电量更少。
确保为这两种情况启用位置服务。
答案 1 :(得分：1)
您应该处理Location为null的情况，并回退到合理的默认值，例如将地图置于主要城市的中心位置。 Google的文档说明了位置can be null in rare cases。在实践中，我发现这种情况最常发生在设备已经在室内很长时间，或者已经禁用了位置服务时。
答案 2 :(得分：1)
public class SplashScreen extends Activity implements GoogleApiClient.ConnectionCallbacks,
GoogleApiClient.OnConnectionFailedListener {
// LogCat tag
private static final String TAG = MainActivity.class.getSimpleName();
private final static int PLAY_SERVICES_RESOLUTION_REQUEST = 1000;
private Location mLastLocation;
// Google client to interact with Google API
private GoogleApiClient mGoogleApiClient;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.splash_screen);
CheckGPS();
ImageView textView = (ImageView) findViewById(R.id.center);
Animation logoMoveAnimation = AnimationUtils.loadAnimation(this, R.anim.splash);
textView.startAnimation(logoMoveAnimation);
}
private void setUpLocation() {
// First we need to check availability of play services
if (checkPlayServices()) {
// Building the GoogleApi client
buildGoogleApiClient();
}
}
/**
* Method to display the location on UI
*/
private void displayLocation() {
mLastLocation = LocationServices.FusedLocationApi
.getLastLocation(mGoogleApiClient);
if (mLastLocation != null) {
double latitude = mLastLocation.getLatitude();
double longitude = mLastLocation.getLongitude();
getCities(latitude, longitude);
new Handler().postDelayed(new Runnable() {
@Override
public void run() {
startActivity(new Intent(SplashScreen.this, MainActivity.class));
finish();
}
}, 4000);
} else {
new Handler().postDelayed(new Runnable() {
@Override
public void run() {
startActivity(new Intent(SplashScreen.this, MainActivity.class));
finish();
}
}, 4000);
}
}
private void getCities(double lat, double lng) {
Geocoder geocoder = new Geocoder(this, Locale.getDefault());
List<Address> addresses = null;
try {
addresses = geocoder.getFromLocation(lat, lng, 1);
String cityName = addresses.get(0).getLocality();
//String locality = addresses.get(0).getSubLocality();
API.OnCityID(SplashScreen.this, cityName);
} catch (IOException e) {
e.printStackTrace();
}
}
/**
* Creating google api client object
*/
protected synchronized void buildGoogleApiClient() {
mGoogleApiClient = new GoogleApiClient.Builder(this)
.addConnectionCallbacks(this)
.addOnConnectionFailedListener(this)
.addApi(LocationServices.API).build();
}
/**
* Method to verify google play services on the device
*/
private boolean checkPlayServices() {
int resultCode = GooglePlayServicesUtil
.isGooglePlayServicesAvailable(this);
if (resultCode != ConnectionResult.SUCCESS) {
if (GooglePlayServicesUtil.isUserRecoverableError(resultCode)) {
GooglePlayServicesUtil.getErrorDialog(resultCode, this,
PLAY_SERVICES_RESOLUTION_REQUEST).show();
} else {
Toast.makeText(getApplicationContext(),
"This device is not supported.", Toast.LENGTH_LONG)
.show();
finish();
}
return false;
}
return true;
}
@Override
protected void onStart() {
super.onStart();
if (mGoogleApiClient != null) {
mGoogleApiClient.connect();
}
}
@Override
protected void onResume() {
super.onResume();
checkPlayServices();
}
/**
* Google api callback methods
*/
@Override
public void onConnectionFailed(ConnectionResult result) {
Log.i(TAG, "Connection failed: ConnectionResult.getErrorCode() = "
+ result.getErrorCode());
}
@Override
public void onConnected(Bundle arg0) {
// Once connected with google api, get the location
displayLocation();
}
@Override
public void onConnectionSuspended(int arg0) {
mGoogleApiClient.connect();
}
private void CheckGPS() {
// Get Location Manager and check for GPS & Network location services
LocationManager lm = (LocationManager) getSystemService(LOCATION_SERVICE);
if (!lm.isProviderEnabled(LocationManager.GPS_PROVIDER) ||
!lm.isProviderEnabled(LocationManager.NETWORK_PROVIDER)) {
// Build the alert dialog
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("Location Services Not Active");
builder.setMessage("Please enable Location Services and GPS");
builder.setPositiveButton("Setting", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialogInterface, int i) {
// Show location settings when the user acknowledges the alert dialog
Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
startActivity(intent);
finish();
}
});
builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialogInterface, int i) {
// Show location settings when the user acknowledges the alert dialog
dialogInterface.dismiss();
new Handler().postDelayed(new Runnable() {
@Override
public void run() {
startActivity(new Intent(SplashScreen.this, MainActivity.class));
finish();
}
}, 1500);
}
});
Dialog alertDialog = builder.create();
alertDialog.setCanceledOnTouchOutside(false);
alertDialog.show();
} else {
setUpLocation();
}
}
}