所以当Activity首次运行并且应用程序崩溃时我不断收到错误。当我重新打开应用程序时，代码运行良好而没有错误...我猜我的代码试图将String转换为Double之前'Lng + Lat'字符串实际上包含一个值（在用户定位之前）。如何防止此问题发生（不使用字符串中的虚拟数据）？请参阅下面的代码。错误发生在第326行。
public class nearMe extends AppCompatActivity implements OnMapReadyCallback {
private MapView mapView;
public GoogleMap gmap;
private static final String MAP_VIEW_BUNDLE_KEY = "MapViewBundleKey";
ActionBar actionBar;
LocationManager locationManager;
LocationListener locationListener;
private List<Station> stationList = new ArrayList<>();
private RecyclerView recyclerView;
private stationAdapter mAdapter;
/* LOCATION STUFF */
@Override
public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
super.onRequestPermissionsResult(requestCode, permissions, grantResults);
if (requestCode == 1) {
if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
startListening();
}
}
}
public void startListening() {
if (ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) == PackageManager.PERMISSION_GRANTED) {
locationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);
updateMap();
}
}
// Dummy Location Co-ordinates - Covent garden
private String lat = "";
private String lng = "";
public void updateLocationInfo(Location location) {
lat = "" + location.getLatitude();
lng = "" + location.getLongitude();
}
//BUTTON TO UPDATE LOCATION IN ACTIONBAR
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_location, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
getNearestStations();
updateMap();
Toast.makeText(this, "Location Updated!", Toast.LENGTH_SHORT).show();
return super.onOptionsItemSelected(item);
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_near_me);
recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
actionBar = getSupportActionBar();
actionBar.setBackgroundDrawable(new ColorDrawable(Color.parseColor("#4c4c4c")));
actionBar.setTitle("Nearest Stations");
mAdapter = new stationAdapter(stationList);
RecyclerView.LayoutManager mLayoutManager = new LinearLayoutManager(getApplicationContext());
recyclerView.setLayoutManager(mLayoutManager);
recyclerView.setItemAnimator(new DefaultItemAnimator());
recyclerView.setAdapter(mAdapter);
// onClick
recyclerView.addOnItemTouchListener(new TouchListener(getApplicationContext(), recyclerView, new ClickListener() {
@Override
public void onClick(View view, int position) {
// Toast.makeText(getApplicationContext(), stationList.get(position).getStation() + "", Toast.LENGTH_SHORT).show();
String findStation = stationList.get(position).getStation();
Uri gmmIntentUri = Uri.parse("google.navigation:q="+findStation+"underground station+London&mode=w");
Intent mapIntent = new Intent(Intent.ACTION_VIEW, gmmIntentUri);
mapIntent.setPackage("com.google.android.apps.maps");
mapIntent.setFlags(mapIntent.FLAG_ACTIVITY_CLEAR_TOP);
if (mapIntent.resolveActivity(getPackageManager()) != null) {
startActivity(mapIntent);
}
}
}));
locationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);
locationListener = new LocationListener() {
@Override
public void onLocationChanged(Location location) {
updateLocationInfo(location);
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}
@Override
public void onProviderEnabled(String provider) {
}
@Override
public void onProviderDisabled(String provider) {
}
};
// PERMISSIONS CHECK FOR MARSHMALLOW AND LATER!
if (Build.VERSION.SDK_INT < 23) {
startListening();
} else {
if (ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, 1);
} else {
locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locationListener);
Location location = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);
if (location != null) {
updateLocationInfo(location);
}
}
}
// insert Stations in to recycler
getNearestStations();
//map
Bundle mapViewBundle = null;
if (savedInstanceState != null) {
mapViewBundle = savedInstanceState.getBundle(MAP_VIEW_BUNDLE_KEY);
}
mapView = (MapView) findViewById(R.id.map_view);
mapView.onCreate(mapViewBundle);
mapView.getMapAsync(this);
}
// clear adapter before adding
public void clear() {
int size = this.stationList.size();
this.stationList.clear();
mAdapter.notifyItemRangeRemoved(0, size);
}
public void getNearestStations(){
RequestQueue queue = Volley.newRequestQueue(this);
String url = "https://transportapi.com/v3/uk/tube/stations/near.json?app_id=157c4895&app_key=091697cea8bae89519dd02ebb318fc51&lat=" + lat + "&lon=" + lng + "&rpp=5";
final StringRequest stringRequest = new StringRequest(url, new Response.Listener<String>() {
@Override
public void onResponse(String response) {
try {
JSONObject jsonObject = new JSONObject(response);
JSONArray jsonArray = jsonObject.getJSONArray("stations");
// Call 'Clear' method to clear mAdapter before adding new data
clear();
if (jsonArray.length() > 0) {
for (int i = 0; i < jsonArray.length(); i++) {
JSONObject jObject = jsonArray.getJSONObject(i);
String station = jObject.getString("name");
Station newStation = new Station(station);
stationList.add(newStation);
mAdapter.notifyDataSetChanged();
}
}else{
Station newStation = new Station("No stations near");
stationList.add(newStation);
mAdapter.notifyDataSetChanged();
// Show a diaog
AlertDialog alertDialog = new AlertDialog.Builder(nearMe.this).create();
alertDialog.setTitle("No Stations Found");
alertDialog.setMessage("You are either not in London or you have no network connectivity.");
alertDialog.setButton(AlertDialog.BUTTON_NEUTRAL, "OK",
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
}
}); alertDialog.show();
}
} catch (JSONException e) { }
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
}
});
RequestQueue requestQueue = Volley.newRequestQueue(getApplicationContext());
requestQueue.add(stringRequest);
}
// maps
@Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
Bundle mapViewBundle = outState.getBundle(MAP_VIEW_BUNDLE_KEY);
if (mapViewBundle == null) {
mapViewBundle = new Bundle();
outState.putBundle(MAP_VIEW_BUNDLE_KEY, mapViewBundle);
}
mapView.onSaveInstanceState(mapViewBundle);
}
@Override
protected void onResume() {
super.onResume();
mapView.onResume();
}
@Override
protected void onStart() {
super.onStart();
mapView.onStart();
}
@Override
protected void onStop() {
super.onStop();
mapView.onStop();
}
@Override
protected void onPause() {
mapView.onPause();
super.onPause();
}
@Override
protected void onDestroy() {
mapView.onDestroy();
super.onDestroy();
}
@Override
public void onLowMemory() {
super.onLowMemory();
mapView.onLowMemory();
}
@Override
public void onMapReady(GoogleMap googleMap) {
gmap = googleMap;
updateMap();
}
public void updateMap () {
double longitude = Double.parseDouble(lng);
double latitude = Double.parseDouble(lat);
gmap.clear();
gmap.setMinZoomPreference(12);
LatLng ldn = new LatLng(latitude, longitude);
gmap.moveCamera(CameraUpdateFactory.newLatLng(ldn));
gmap.addMarker(new MarkerOptions()
.position(new LatLng(latitude, longitude))
.icon(BitmapDescriptorFactory.fromResource(R.drawable.mapmarker)));
}
}