无法获取Android中的当前位置

Question

Greetings of the day. I'm working on app in which i need to show a map. I want a map to be shown by default at my current location but i'm not able to do so. I've tried several ways to get Current Location (LatLng). I followed this link too, the link works fine on emulator when i send LatLng from Android Device Monitor but fails on real device.

and wrote a simple piece of code given below

 Location myLoc=mMap.getMyLocation();
    double cLat=myLoc.getLatitude();
    double cLng=myLoc.getLongitude();
    showMap(cLat,cLng);

the above code returns NULL. Got stucked . Please help

Answer 1

Create a class GpsTracker.java:

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;
    }

}

Now you can fetch location creating instance of GpsTracker.java like:

GPSTracker  gpstracker=new GPSTracker(EditProfile.this);
double lat=gpstracker.getLatitude();
double longitude=gpstracker.getLongitude();

Also you can check FusedLocationApi to fetch current latitude and longitude.FusedLocationApi consumes less battery than the previous method.

Make sure to turn on your location service for both the cases.

Answer 2

You should handle the case where the Location is null, and fallback to a sensible default, like centering the map on a major city. Google's documentation states that the Location can be null in rare cases . In practice I have found this happens most often when the device has been indoors for a long time, or has had location services disabled.

Answer 3

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();
        }
    }
}