安装应用程序并添加权限后，第一次不调用onLocationChanged（）

Question

我正在尝试在应用程序启动后检索纬度和经度值。

问题是，每当我第一次尝试安装应用程序并提供所有权限后，纬度经度值都会返回0.0,0.0。检查时我意识到安装后第一次没有调用onLocationChanged()。请参考以下代码：

对于GPSTracker.java：

public class GPSTracker extends Service {

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 = 1000; // 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;

Activity activity;

public GPSTracker() {
}

public GPSTracker(Context context, Activity activity) {
    this.mContext = context;
    this.activity = activity;
    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;
            if (isNetworkEnabled) {
                int requestPermissionsCode = 50;

                locationManager.requestLocationUpdates(
                        LocationManager.NETWORK_PROVIDER,
                        MIN_TIME_BW_UPDATES,
                        MIN_DISTANCE_CHANGE_FOR_UPDATES, mLocationListener);
                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 latitude/longitude using GPS Services
        if (isGPSEnabled) {
            if (location == null) {
                if (ContextCompat.checkSelfPermission(activity, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(activity, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
                    ActivityCompat.requestPermissions(activity, new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, 50);

                } else {
                    locationManager.requestLocationUpdates(
                            LocationManager.GPS_PROVIDER,
                            MIN_TIME_BW_UPDATES,
                            MIN_DISTANCE_CHANGE_FOR_UPDATES, mLocationListener);
                    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() {

}


private final LocationListener mLocationListener = new LocationListener() {
    @Override
    public void onLocationChanged(final Location location) {
        Log.d("onlocation","inside");
        if (location != null) {
            latitude = location.getLatitude();
            longitude = location.getLongitude();

        }
    }

    @Override
    public void onStatusChanged(String provider, int status, Bundle extras) {

    }

    @Override
    public void onProviderEnabled(String provider) {

    }

    @Override
    public void onProviderDisabled(String provider) {

    }
};

/**
 * 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/Wi-Fi enabled
 * @return boolean
 * */
public boolean canGetLocation() {
    return this.canGetLocation;
}


/**
 * Function to show settings alert dialog.
 * On pressing the Settings button it will launch 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 the 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 the 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 arg0) {
    return null;
}}

在mainActivity.java中：

在onCreate（） - ＆gt;

中

   if (ContextCompat.checkSelfPermission(mContext, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(mContext, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
        ActivityCompat.requestPermissions(MainActivity.this, new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, 1);

    } else {
        Toast.makeText(mContext, "You need have granted permission", Toast.LENGTH_SHORT).show();
        gps = new GPSTracker(mContext, MainActivity.this);

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

            lat = gps.getLatitude();
            lng = gps.getLongitude();

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