这个问题在这里已经有答案了：

什么是nullpointerexception，如何修复它(12个答案）
24天前关门。
对于android开发来说，这是一个相当新的问题，因此很容易解决。
我的应用程序有一个recyclerview，它显示一些要填充的空字段，每个字段都有一个“delete”按钮。当我按DeleteComponent按钮时，会收到以下错误消息：

java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.Integer.intValue()' on a null object reference

我目前的主要活动如下

package com.example.recipecalculator;

import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.EditText;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity implements IngredientsAdapter.IngredientVH.ItemDeleter {

    private RecyclerView recyclerView;
    private RecyclerView.LayoutManager layoutManager;
    public static IngredientsAdapter adapter;
    public static List<Ingredient> ingredients = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        ingredients.add(new Ingredient(0, null, null));

        recyclerView = findViewById(R.id.ingredients_recyclerView);
        layoutManager = new LinearLayoutManager(this);
        adapter = new IngredientsAdapter(this, this);

        recyclerView.setLayoutManager(layoutManager);
        recyclerView.setAdapter(adapter);
    }

    public void addIngredient(View view) {
        ingredients.add(new Ingredient(0, null, null));
        adapter.notifyDataSetChanged();
    }

    @Override
    public void deleteIngredient(Integer position){
        Log.d("CS50", "MAIN ACTIVITY CALLBACK INVOKED");
        ingredients.remove(position);
        adapter.notifyItemRemoved(position);
    }
}

我的适配器类是这样的

package com.example.recipecalculator;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

import java.util.ArrayList;
import java.util.List;

public class IngredientsAdapter extends RecyclerView.Adapter<IngredientsAdapter.IngredientVH> {

    private Context context;
    private IngredientVH.ItemDeleter deleter;

    public static class IngredientVH extends RecyclerView.ViewHolder {

        public EditText quantity;
        public Spinner unitOfMeasure;
        public EditText ingredientName;
        public Button deleteIngredient;
        public ItemDeleter deleter;

        public IngredientVH(View view, Context context, ItemDeleter deleter){
            super(view);
            this.quantity = view.findViewById(R.id.quantity);
            this.ingredientName = view.findViewById(R.id.ingredient_name);
            this.unitOfMeasure = view.findViewById(R.id.unitOfMeasure_spinner);
            this.deleteIngredient = view.findViewById(R.id.delete_icon);

            ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(context,
                    R.array.units_of_measure, android.R.layout.simple_spinner_item);
            adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
            unitOfMeasure.setAdapter(adapter);

            Integer position = (Integer) quantity.getTag();
            this.deleter = deleter;

            deleteIngredient.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    deleter.deleteIngredient(position);
                }
            });
        }

        public interface ItemDeleter {
            void deleteIngredient(Integer position);
        }
    }

    public IngredientsAdapter(Context context, IngredientVH.ItemDeleter deleter){
        super();
        this.context = context;
        this.deleter = deleter;
    }

    @NonNull
    @Override
    public IngredientVH onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.ingredient_row, parent, false);
        return new IngredientVH(view, context, deleter);
    }

    @Override
    public void onBindViewHolder(@NonNull IngredientVH holder, int position) {
        holder.quantity.setTag(position);
    }

    @Override
    public int getItemCount() {
        return MainActivity.ingredients.size();
    }
}

很明显，这与使用deleteComponent按钮单击传递项目位置有关，但无法确定它是什么。
干杯！