When I leave this Fragment and re-enter my LatLng can't be found. Throws np... and yes I know what np's are...maybe it's a Life cycle problem?

I need to use my FINE LOCATION for one of the features in my app. I know what null pointers are and I realize that it means that it can't get my location, but I don't understand why not because sometimes it works fine, no crashes for a prolonged period of time, and then if I exit the Activity and then try to re-access it app the app crashes usually.

Why is this happening?

Should I try to save the LatLng value to solve this problem by using the onResume(); method? Not sure why it works and other times my location can't be found...

This is the line throwing the null pointer if (SphericalUtil.computeDistanceBetween(new LatLng(eventLatitude, eventLongitude), myLatLng) < metersToMiles) {
mPostList.add(post);} in the readEventsNearby(); method. I get my location in the getLocation(); method.

The issue is myLatLng which I get as you can see below. Why does it work, and then when I exit the Fragment and re-enter it produces the null pointer?

Fragment

public class EventsNearbyFragment extends Fragment implements SwipeRefreshLayout.OnRefreshListener {
private RecyclerView mRecyclerView;
private PostAdapter mPostAdapter;
private List<Post> mPostList;
private SwipeRefreshLayout mSwipeRefreshLayout;
private ProgressBar mProgressBar2;
private FusedLocationProviderClient mFusedLocationProviderClient;
private double myLatitude, myLongitude;
private LatLng myLatLng;
private TextView mDistance, mNoEventsNearBy;
private Dialog mDialog;
private ProgressBar mProgressBar;
private Button mApply;
private int miles;
double metersToMiles;
@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mFusedLocationProviderClient = LocationServices.getFusedLocationProviderClient(getContext());
if (ActivityCompat.checkSelfPermission(getContext(), Manifest.permission.ACCESS_FINE_LOCATION) == PackageManager.PERMISSION_GRANTED) {
getMyLocation();
} else {
ActivityCompat.requestPermissions(getActivity(), new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, 44);
}
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_events_nearby, container, false);
mProgressBar2 = view.findViewById(R.id.progress_bar);
ImageView backArrow = view.findViewById(R.id.back);
ImageView filterIcon = view.findViewById(R.id.distance_filter);
mNoEventsNearBy = view.findViewById(R.id.no_events_nearby);
mFusedLocationProviderClient = LocationServices.getFusedLocationProviderClient(getContext());
if (ActivityCompat.checkSelfPermission(getContext(), Manifest.permission.ACCESS_FINE_LOCATION) == PackageManager.PERMISSION_GRANTED) {
getMyLocation();
} else {
ActivityCompat.requestPermissions(getActivity(), new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, 44);
}
filterIcon.setOnClickListener(v -> buildDialog());
backArrow.setOnClickListener(v -> getActivity().getSupportFragmentManager().popBackStack());
initializeRecyclerView(view);
setSwipeRefreshLayout(view);
return view;
}
private void buildDialog() {
mDialog = new Dialog(getContext());
mDialog.setContentView(R.layout.seek_bar);
mDistance = mDialog.findViewById(R.id.text_view);
mProgressBar = mDialog.findViewById(R.id.progress_bar);
SeekBar seekBar = mDialog.findViewById(R.id.seek_bar);
mApply = mDialog.findViewById(R.id.apply);
setCancel();
seekBar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
@Override
public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
mProgressBar.setProgress(progress);
mDistance.setText("" + progress + "");
mApply.setOnClickListener(v -> {
SharedPreferences.Editor editor = getActivity().getSharedPreferences("prefs", Context.MODE_PRIVATE).edit();
editor.putInt("miles", progress);
editor.apply();
mDialog.dismiss();
readEventsNearby();
});
}
@Override
public void onStartTrackingTouch(SeekBar seekBar) {
}
@Override
public void onStopTrackingTouch(SeekBar seekBar) {
}
});
mDialog.getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));
mDialog.show();
}
private void setCancel() {
Button cancel = mDialog.findViewById(R.id.cancel);
cancel.setOnClickListener(v -> mDialog.dismiss());
}
private void setSwipeRefreshLayout(View view) {
mSwipeRefreshLayout = view.findViewById(R.id.refresh);
mSwipeRefreshLayout.setOnRefreshListener(this);
mSwipeRefreshLayout.post(() -> {
mSwipeRefreshLayout.setRefreshing(true);
readEventsNearby();
});
}
private void initializeRecyclerView(View view) {
mRecyclerView = view.findViewById(R.id.recycler_view);
mRecyclerView.setHasFixedSize(true);
LinearLayoutManager linearLayoutManager = new LinearLayoutManager(getContext());
linearLayoutManager.setReverseLayout(true);
linearLayoutManager.setStackFromEnd(true);
mRecyclerView.setLayoutManager(linearLayoutManager);
mPostList = new ArrayList<>();
mPostAdapter = new PostAdapter(getContext(), mPostList);
mRecyclerView.setAdapter(mPostAdapter);
if (mRecyclerView.getAdapter().getItemCount() == 0) {
mProgressBar2.setVisibility(View.VISIBLE);
} else {
mProgressBar2.setVisibility(View.GONE);
}
}
private void getMyLocation() {
if (ActivityCompat.checkSelfPermission(getContext(), Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(getContext(), Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
return;
}
Task<Location> task = mFusedLocationProviderClient.getLastLocation();
task.addOnSuccessListener(location -> {
if (location != null) {
myLatitude = location.getLatitude();
myLongitude = location.getLongitude();
// My location
myLatLng = new LatLng(myLatitude, myLongitude);
}
});
}
@Override
public void onResume() {
super.onResume();
}
private void readEventsNearby() {
DatabaseReference reference = FirebaseDatabase.getInstance().getReference("Posts");
reference.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot snapshot) {
mPostList.clear();
for (DataSnapshot dataSnapshot : snapshot.getChildren()) {
Post post = dataSnapshot.getValue(Post.class);
if (post != null && post.getLocation() != null) {
double eventLatitude = post.getLocation().getLatitude();
double eventLongitude = post.getLocation().getLongitude();
SharedPreferences sharedPreferences = getActivity().getSharedPreferences("prefs", Context.MODE_PRIVATE);
miles = sharedPreferences.getInt("miles", 10);
metersToMiles = miles * 1609.344;
if (SphericalUtil.computeDistanceBetween(new LatLng(eventLatitude, eventLongitude), myLatLng) < metersToMiles) {
mPostList.add(post);
}
}
}
if (mPostList.size() == 0) {
mProgressBar2.setVisibility(View.GONE);
mNoEventsNearBy.setVisibility(View.VISIBLE);
} else {
mProgressBar2.setVisibility(View.GONE);
mNoEventsNearBy.setVisibility(View.GONE);
}
mPostAdapter = new PostAdapter(getContext(), mPostList);
mRecyclerView.setAdapter(mPostAdapter);
mPostAdapter.notifyDataSetChanged();
mSwipeRefreshLayout.setRefreshing(false);
}
@Override
public void onCancelled(@NonNull DatabaseError error) {
mSwipeRefreshLayout.setRefreshing(false);
}
});
}
@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
if (requestCode == 44) {
if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
getMyLocation();
}
}
}
@Override
public void onRefresh() {
readEventsNearby();
}
}

It's crashing because the myLatLng variable is null when executing SphericalUtil.computeDistanceBetween(new LatLng(eventLatitude, eventLongitude), myLatLng)

This may happen because of some of the following possibilities:

1. You added a success listener to mFusedLocationProviderClient.getLastLocation() and it may not be succeeding, therefore myLatLng is never assigned and will be null.
2. It may succeed but for some reason you are executing SphericalUtil.computeDistanceBetween(new LatLng(eventLatitude, eventLongitude), myLatLng) before that, therefore myLatLng is still null.

I suggest you to check for the nullability of myLatLng before executing SphericalUtil.computeDistanceBetween(new LatLng(eventLatitude, eventLongitude), myLatLng) and react according to it.