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什么是nullpointerexception，如何修复它(（12个答案）
6天前关门。
我已经使用android studio在java中构建了一个RecycleWeber应用程序。当我运行应用程序时，它崩溃了，当我检查logcat时，我发现我的适配器中有一个空指针异常。 onBindViewHolder 方法。这包括第49行。

@Override
    public void onBindViewHolder(@NonNull ContactsAdapter.ViewHolder holder, int position) {
        holder.txtName.setText(contacts.get(position).getName());
        holder.txtName.setText(contacts.get(position).getEmail());
        Glide.with(context).asBitmap().load(contacts.get(position).getImage()).into(holder.image);

        holder.parent.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Toast.makeText(context, contacts.get(position).getName() + " Clicked", Toast.LENGTH_SHORT).show();
            }
        });

    }

logcat日志

java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.cardview.widget.CardView.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
        at com.example.learningapplication.ContactsAdapter.onBindViewHolder(ContactsAdapter.java:49)
        at com.example.learningapplication.ContactsAdapter.onBindViewHolder(ContactsAdapter.java:19)

编辑：以下是完整代码：

package com.example.learningapplication;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;

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

import com.bumptech.glide.Glide;

import java.util.ArrayList;

public class ContactsAdapter extends RecyclerView.Adapter<ContactsAdapter.ViewHolder>{
    private Context context;

    ArrayList<Contacts> contacts = new ArrayList<>();

    public void setContacts(ArrayList<Contacts> contacts) {
        this.contacts = contacts;
        notifyDataSetChanged();
    }

    public ContactsAdapter(Context context) {
        this.context = context;
    }

    public ContactsAdapter() {
    }

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

    @Override
    public void onBindViewHolder(@NonNull ContactsAdapter.ViewHolder holder, int position) {
        holder.txtName.setText(contacts.get(position).getName());
        holder.txtName.setText(contacts.get(position).getEmail());
        Glide.with(context).asBitmap().load(contacts.get(position).getImage()).into(holder.image);

        holder.parent.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Toast.makeText(context, contacts.get(position).getName() + " Clicked", Toast.LENGTH_SHORT).show();
            }
        });

    }

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

    public static class ViewHolder extends RecyclerView.ViewHolder{
        private TextView txtName;
        private TextView txtEmail;
        private ImageView image;
        private CardView parent;

        public ViewHolder(@NonNull View itemView) {
            super(itemView);
            txtName = itemView.findViewById(R.id.txtName);
            txtEmail = itemView.findViewById(R.id.txtEmail);
            image = itemView.findViewById(R.id.image);

        }

    }
}

``