取消装箱hashmap.get（）会产生NullPointerException

Question

I'm using a hashmap to get data from another class. I check the logcat and the data for hashmap has been set and it contains the key. But when I try to get the hashmap from the other class I'm getting NullPointerException and when I try to check if the map contains the key it doesn't

 @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.continueItem:
                CustomAdapter a = new CustomAdapter();
                CustomAdapter.InputTextListener i = a.new InputTextListener();
                HashMap<String, Integer> hashMap = i.getHashMap();
                inputTime = hashMap.get("EDITTEXT VALUE");
                Log.d(TAG, "onOptionsItemSelected: " + hashMap.get("EDITTEXT VALUE"));
                Log.d(TAG, "onOptionsItemSelected: " + hashMap.containsKey("EDITTEXT VALUE"));
                retrieveInputTime(inputTime);
                break;

        }
        return super.onOptionsItemSelected(item);
    }

public class CustomAdapter extends RecyclerView.Adapter<CustomAdapter.ViewHolder> {

    private static final String TAG = "CustomAdapter";
    private ArrayList<Integer> mWorkTW = new ArrayList<>();
    private ArrayList<Integer> mWorkET = new ArrayList<>();
    private ArrayList<Integer> mRestTW = new ArrayList<>();
    private ArrayList<Integer> mRestET = new ArrayList<>();
    private Context mContext;
    private int numberOfIntervals;

    public CustomAdapter() {

    }

    public CustomAdapter(Context context, ArrayList<Integer> mWorkTW, ArrayList<Integer> mWorkET, ArrayList<Integer> mRestTW, ArrayList<Integer> mRestET, int numberOfIntervals) {

        this.mWorkTW = mWorkTW;
        this.mWorkET = mWorkET;
        this.mRestTW = mRestTW;
        this.mRestET = mRestET;
        this.mContext = context;
        this.numberOfIntervals = numberOfIntervals;
        //this.inputTimeIntegerWET = inputTimeIntegerWET;

        Log.d(TAG, "CustomAdapter: " + numberOfIntervals);
    }


    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
        View customView = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.time_row, viewGroup, false);
        ViewHolder holder = new ViewHolder(customView, new InputTextListener());
        return holder;

    }

    @Override
    public void onBindViewHolder(@NonNull final ViewHolder viewHolder, final int i) {
        Log.d(TAG, "onBindViewHolder: called");
        viewHolder.workTextView.setText(R.string.work_text_view);
        viewHolder.restTextView.setText(R.string.rest_text_view);
        viewHolder.workEditText.setOnFocusChangeListener(new View.OnFocusChangeListener() {
            public void onFocusChange(View v, boolean hasFocus) {
                if (hasFocus)
                    viewHolder.workEditText.setHint("");
                else
                    viewHolder.workEditText.setHint(mWorkET.get(viewHolder.getAdapterPosition()));
            }
        });

        viewHolder.restEditText.setOnFocusChangeListener(new View.OnFocusChangeListener() {
            public void onFocusChange(View v, boolean hasFocus) {
                if (hasFocus)
                    viewHolder.restEditText.setHint("");
                else
                    viewHolder.restEditText.setHint(mRestET.get(viewHolder.getAdapterPosition()));
            }
        });
    }

    @Override
    public int getItemCount() {
        Log.d(TAG, "" + numberOfIntervals);
        return numberOfIntervals;
    }

    public class ViewHolder extends RecyclerView.ViewHolder {

        public InputTextListener inputTextListener;
        TextView workTextView;
        EditText workEditText;
        TextView restTextView;
        EditText restEditText;
        ConstraintLayout parentLayout;




        public ViewHolder(@NonNull View itemView, InputTextListener inputTextListener) {
            super(itemView);
            workTextView = itemView.findViewById(R.id.workTextView);
            workEditText = itemView.findViewById(R.id.workEditText);
            restTextView = itemView.findViewById(R.id.restTextView);
            restEditText = itemView.findViewById(R.id.restEditText);
            parentLayout = itemView.findViewById(R.id.parentLayout);
            this.inputTextListener = inputTextListener;


            workEditText.addTextChangedListener(inputTextListener);
        }
    }

        class InputTextListener implements TextWatcher {
        String inputTimeString;

        int inputTime;
        HashMap<String, Integer> hashMap = new HashMap<String, Integer>();

            public HashMap<String, Integer> getHashMap() {
                return hashMap;
            }

            public InputTextListener() {
            }

            public void setHashMap(HashMap<String, Integer> hashMap) {
                this.hashMap = hashMap;
            }

            /*public int getInputTime() {
            return inputTime;
        }*/

        public void setInputTime(int inputTime) {
            this.inputTime= inputTime;
        }

        @Override
        public void beforeTextChanged(CharSequence s, int start, int count, int after) {

        }

        @Override
        public void onTextChanged(CharSequence s, int start, int before, int count) {
             try {
                 Log.d(TAG, "onTextChanged: I've made it to here!");
                 inputTimeString = s.toString().trim();
                 inputTime = Integer.parseInt(inputTimeString);
                 setInputTime(inputTime);
                 hashMap.put("EDITTEXT VALUE", inputTime);
                 Log.d(TAG, "onTextChanged: " + inputTime);

                 int bla = inputTime + 2;
                 Log.d(TAG, "onTextChanged: " + bla);
                 Log.d(TAG, "onTextChanged: " + hashMap.containsKey("EDITTEXT VALUE"));
                 Log.d(TAG, "onTextChanged: " + hashMap.get("EDITTEXT VALUE"));
                 setHashMap(hashMap);

             } catch (NumberFormatException NFE) {
                 mWorkET = null;
             }



        }

        @Override
        public void afterTextChanged(Editable s) {

        }


    }
}

I'm expecting for the hashmap being able to access the data from the other class.

Answer 1

Here is some of the code you posted:

 CustomAdapter a = new CustomAdapter(); CustomAdapter.InputTextListener i = a.new InputTextListener(); HashMap<String, Integer> hashMap = i.getHashMap(); 

What this is going to do is create a new instance of your CustomAdapter class, then create a new instance of your InputTextListener class, and finally retrieve the HashMap stored inside the text listener.

Again, this is all happening with new instances of these classes. Therefore, the HashMap is empty (since nothing has populated it).

You are probably assuming that i would be the "same" listener instance as you're using elsewhere in your app. This is not the case. You will need to access that listener somehow rather than creating a new instance.

Looking at your code, this doesn't really seem feasible. Each ViewHolder has its own instance of InputTextListener ... how will your options menu know which ViewHolder you're trying to interact with?

Chances are good that you're going to need to go back to the drawing board and come up with a different way to solve whatever problem you're attempting.