Toast 消息显示纬度和经度均为 0

Question

我正在尝试从here 构建一个应用程序，用户单击button 并获取当前的纬度和经度，但问题是我得到0.0 的纬度和经度。我的应用程序中有一个activity 和一个service。 activity 和 service 的代码如下：

GpsActivity.java

    public class GpsActivity extends AppCompatActivity {

    Button show;
    private static final int REQUEST_CODE_PERMISSION = 2;
    String mPermission = Manifest.permission.ACCESS_FINE_LOCATION;

    GPSTracker gps;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_gps);

        try {
            if (ActivityCompat.checkSelfPermission(this, mPermission)
                    != PackageManager.PERMISSION_GRANTED) {

                ActivityCompat.requestPermissions(this, new String[]{mPermission},
                        REQUEST_CODE_PERMISSION);

//                If any permission above not allowed by user, this condition will
//                execute every time, else your else part will work
            }
        } catch (Exception e) {
            e.printStackTrace();
        }

        show=(Button)findViewById(R.id.showLocation);

        show.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                gps=new GPSTracker(GpsActivity.this);

                // check if GPS enabled
                if(gps.canGetLocation()){

                    double latitude = gps.getLatitude();
                    double longitude = gps.getLongitude();

                    // \n is for new line
                    Toast.makeText(getApplicationContext(), "Your Location is - \nLat: "
                            + latitude + "\nLong: " + longitude, Toast.LENGTH_LONG).show();
                }else{
                    // can't get location
                    // GPS or Network is not enabled
                    // Ask user to enable GPS/network in settings
                    gps.showSettingsAlert();
                }
            }
        });
    }
}

GPSTracker.java

public class GPSTracker extends Service implements LocationListener {
    private 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

    protected LocationManager locationManager;

    public GPSTracker() {
        //mContext = null;
    }

    public GPSTracker(Context mContext) {
        this.mContext = mContext;
        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
            } else {
                this.canGetLocation = true;
                // First get location from Network Provider
                if (isNetworkEnabled) {
                    if (ActivityCompat.checkSelfPermission(this,
                            Manifest.permission.ACCESS_FINE_LOCATION)
                            != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this,
                            Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
                        // TODO: Consider calling
                        //    ActivityCompat#requestPermissions
                        // here to request the missing permissions, and then overriding
                        //   public void onRequestPermissionsResult(int requestCode, String[] permissions,
                        //                                          int[] grantResults)
                        // to handle the case where the user grants the permission. See the documentation
                        // for ActivityCompat#requestPermissions for more details.
                        return location;
                    }
                    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
                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();
            }
        });

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


    @Override
    public IBinder onBind(Intent intent) {
        // TODO: Return the communication channel to the service.
        return null;
    }

    @Override
    public void onLocationChanged(Location location) {

    }

    @Override
    public void onStatusChanged(String s, int i, Bundle bundle) {

    }

    @Override
    public void onProviderEnabled(String s) {

    }

    @Override
    public void onProviderDisabled(String s) {

    }
}

我已经在manifest 文件中提到了位置更新所需的所有permissions。这里唯一的问题是latitude 和longitude 在单击按钮时显示0.0。

有人可以帮忙吗？谢谢你:)

Answer 1

你没有调用getLocation()方法

if(gps.canGetLocation())
{
    gps.getLocation();
    double latitude = gps.getLatitude();
    double longitude = gps.getLongitude();

    // \n is for new line
    Toast.makeText(getApplicationContext(), "Your Location is - \nLat: "
            + latitude + "\nLong: " + longitude, Toast.LENGTH_LONG).show();
}

Answer 2

函数getLastKnownLocation() 正在返回null。我建议等待一个新的位置在onLocationChanged() 中被调用并使用该位置对象。

另外，您没有正确使用Service 类。您基本上围绕LocationManager 创建了一个包装器。如果您想知道如何正确使用Service，请查看此tutorial。