java - 在 Android Google Map API 中的 onMayReady() 处获取初始坐标

Question

我正在实现 Google map API，其中我尝试在 onMapReady() 处获取初始位置。

mCurrentLocation 应该是存储位置的变量，因此我尝试在 onMapReady() 中的日志中输出该变量，但在开始时 mCurrentLocation > 为 null，所以首先我必须请求一个位置。我对api不熟悉。我做了一个猜测，并将 startLocationUpdates(this) 放在前面。

@Override
public void onMapReady(GoogleMap googleMap) {
    mMap = googleMap;
    mMap.getUiSettings().setZoomControlsEnabled(true);
    mMap.setMyLocationEnabled(true);

    LatLng sydney = new LatLng(-34, 151);
    mMap.addMarker(new MarkerOptions().position(sydney).title("Marker in Sydney"));
    mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(sydney, 14.0f));

    // Start the update??
    startLocationUpdates(this);
    // This is where I want to retrieve the location coordinates
    Log.w("Location", "Current reading: " + mCurrentLocation.toString());
}

没成功。在堆栈跟踪中，它显示java.lang.NullPointerException:尝试在空对象引用上调用虚拟方法“java.lang.String android.location.Location.toString()”。我还尝试了其他方法，例如 initLocation()，但它也不起作用。

这是代码的其余部分:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
            .findFragmentById(R.id.map);
    mapFragment.getMapAsync(this);
    initLocations();
}

@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
    switch (requestCode) {
        case ACCESS_FINE_LOCATION: {
            if (grantResults.length > 0
                    && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                mFusedLocationClient.requestLocationUpdates(mLocationRequest,
                        mLocationCallback, null /* Looper */);
            }
            return;
        }
    }
}

private void initLocations() {
    if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
        if (ActivityCompat.shouldShowRequestPermissionRationale(this,
                Manifest.permission.ACCESS_FINE_LOCATION)) {
        } else {
            ActivityCompat.requestPermissions(this,
                    new String[]{Manifest.permission.ACCESS_FINE_LOCATION},
                    ACCESS_FINE_LOCATION);
        }
        return;
    }
}

private void startLocationUpdates(Context context) {
    Intent intent = new Intent(context, LocationService.class);
    mLocationPendingIntent = PendingIntent.getService(context, 1, intent, PendingIntent.FLAG_UPDATE_CURRENT);
    if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) == PackageManager.PERMISSION_GRANTED
            || ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) == PackageManager.PERMISSION_GRANTED) {
        Task<Void> locationTask = mFusedLocationClient.requestLocationUpdates(mLocationRequest,
                mLocationPendingIntent);
        if (locationTask != null) {
            locationTask.addOnFailureListener(new OnFailureListener() {
                @Override
                public void onFailure(@NonNull Exception e) {
                    if (e instanceof ApiException) {
                        Log.w("Main2Activity", ((ApiException) e).getStatusMessage());
                    } else {
                        Log.w("Main2Activity", e.getMessage());
                    }
                }
            });

            locationTask.addOnCompleteListener(new OnCompleteListener<Void>() {
                @Override
                public void onComplete(@NonNull Task<Void> task) {
                    Log.d("Main2Activity", "restarting gps successful!");
                }
            });


        }
    }
}

private void stopLocationUpdates(){
    mFusedLocationClient.removeLocationUpdates(mLocationCallback);
}

@Override
protected void onResume() {
    super.onResume();
    mLocationRequest = new LocationRequest();
    mLocationRequest.setInterval(10000);
    mLocationRequest.setFastestInterval(5000);
    mLocationRequest.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);
    mFusedLocationClient = LocationServices.getFusedLocationProviderClient(this);
    accelerometer.startAccelerometerRecording();

}

private Location mCurrentLocation;
private String mLastUpdateTime;
LocationCallback mLocationCallback = new LocationCallback() {
    @Override
    public void onLocationResult(LocationResult locationResult) {
        super.onLocationResult(locationResult);
        mCurrentLocation = locationResult.getLastLocation();
        mLastUpdateTime = DateFormat.getTimeInstance().format(new Date());
        Log.i("MAP", "new location " + mCurrentLocation.toString());
        if (mMap != null)
            mMap.addMarker(new MarkerOptions().position(new LatLng(mCurrentLocation.getLatitude(), mCurrentLocation.getLongitude()))
                    .title(mLastUpdateTime));
        mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(new LatLng(mCurrentLocation.getLatitude(), mCurrentLocation.getLongitude()), 14.0f));
    }
};

请求位置的正确方法是什么？

Answer 1

我总是使用 LocationManager 来获取当前位置，并确保您当前的 GPS 已打开。

final LocationManager locationManager = (LocationManager) getApplicationContext().getSystemService(Context.LOCATION_SERVICE);
Criteria criteria = new Criteria();
criteria.setAccuracy(Criteria.ACCURACY_FINE);
locationManager.requestSingleUpdate(criteria, new LocationListener() {
                @Override
                public void onLocationChanged(Location location) {
                    // this is where you get the location location.getLatitude(), location.getLongitude()
                }

                @Override public void onStatusChanged(String provider, int status, Bundle extras) { }
                @Override public void onProviderEnabled(String provider) { }
                @Override public void onProviderDisabled(String provider) { }
            }, null);