取消装箱hashmap.get（）会产生NullPointerException

Question

我正在使用哈希图从另一个类获取数据。 我检查了logcat，并设置了hashmap的数据，其中包含密钥。 但是，当我尝试从另一个类获取哈希图时，我得到了NullPointerException，并且当我尝试检查地图是否包含键时，它没有

 @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) {

        }


    }
}

我期望哈希图能够访问其他类的数据。

Answer 1

这是您发布的一些代码：

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

这将要做的是创建CustomAdapter类的新实例，然后创建InputTextListener类的新实例，最后检索存储在文本侦听器中的HashMap 。

同样，这些都是在这些类的新实例中发生的。 因此， HashMap为空（因为没有填充它）。

您可能会假设i将成为您在应用程序其他位置使用的“相同”侦听器实例。 不是这种情况。 您将需要以某种方式访问​​该侦听器，而不是创建一个新实例。

查看您的代码，这似乎并不可行。 每个ViewHolder都有其自己的InputTextListener实例...您的选项菜单如何知道您要与哪个ViewHolder进行交互？

您很有可能需要回到绘图板上，并提出另一种方法来解决您尝试的任何问题。