Question

我正在android studio中编程，这是我的代码段：

public class settingsView extends Fragment {

    public settingsView() {
    }

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

        final Spinner citySpinner = (Spinner) getActivity().findViewById(R.id.citySpinner);

        FirebaseDatabase.getInstance().getReference("/movies/karnataka").addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

                ArrayList<String> cityList = new ArrayList<>();

                for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                    cityList.add(snapshot.getKey());
                }

                Log.d("firebasedata", cityList.toString());

                ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity().getApplicationContext(), android.R.layout.simple_spinner_item, cityList );
                adapter.setDropDownViewResource(android.R.layout.simple_spinner_item);
                citySpinner.setAdapter(adapter);
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
            }
        });


        return inflater.inflate(R.layout.settingsview, container, false);
    }
}

我得到

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Spinner.setAdapter(android.widget.SpinnerAdapter) on a null object reference exception

在线：

citySpinner.setAdapter(adapter)

Answer 1

您需要首先在oncreateview中为具有片段视图的xml文件充气。

然后使用该视图执行findviewbyid：

view = inflater.inflate(R.layout.fragment_xml, container, false);
final Spinner citySpinner = (Spinner) view.findViewById(R.id.citySpinner);

Answer 2

您需要在视图中找到微调器。在onCreateView方法中尝试以下方法：

 @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

        View v = inflater.inflate(R.layout.settingsview, container, false);

        final Spinner citySpinner = (Spinner) v.findViewById(R.id.citySpinner); // you use it here


        return v;
    }

为什么在这里出现微调器的空引用错误？

2 个答案: