我想删除 listView 的数据并出现这个异常 java.lang.NullPointerException
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【中文标题】我想删除 listView 的数据并出现这个异常 java.lang.NullPointerException【英文标题】：I want to delete data of listView and appears this exception java.lang.NullPointerException 【发布时间】：2020-10-30 21:45:22 【问题描述】：嗯，我正在做一个安卓应用程序。 我有一个 listView 来显示我的 Firebase 的数据，这个 listView 有带有 textView 和删除按钮的行，当我想删除某个数据时，我单击删除按钮但出现这个错误 java.lang.NullPointerException: Attempt to invoke virtual空对象引用上的方法 'void android.widget.TextView.setText(java.lang.CharSequence)'
CustomAdapterData.java
public View getView(final int position, View convertView, ViewGroup parent)
Data data = new Data();
if(convertView == null)
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
assert inflater != null;
convertView = inflater.inflate(R.layout.list_data, null);
data.date = convertView.findViewById(R.id.date);
data.age = convertView.findViewById(R.id.age);
data.height = convertView.findViewById(R.id.height);
data.weight = convertView.findViewById(R.id.weight);
data.imc = convertView.findViewById(R.id.imc);
data.date.setText(list.get(position).getDate());
data.age.setText(list.get(position).getAge());
data.height.setText(list.get(position).getHeight());
data.weight.setText(list.get(position).getWeight());
data.imc.setText(list.get(position).getImc());
Button btDel = convertView.findViewById(R.id.btDelete);
btDel.setOnClickListener(new View.OnClickListener()
@Override
public void onClick(View v)
Data data = new Data();
db.document(list.get(position).getDate())
.delete()
.addOnSuccessListener(new OnSuccessListener<Void>()
@Override
public void onSuccess(Void aVoid)
Log.d("MainActivity", "DocumentSnapshot successfully deleted!");
Toast.makeText(context, "Data deleted", Toast.LENGTH_LONG).show();
)
.addOnFailureListener(new OnFailureListener()
@Override
public void onFailure(@NonNull Exception e)
Log.w("MainActivity", "Error deleting document", e);
Toast.makeText(context, "Data not deleted", Toast.LENGTH_LONG).show();
);
list.remove(list.get(position));
int pos = position;
if (position == list.size())
pos = position - 1;
data.date.setText(list.get(pos).getDate()); <- the error appears here
data.age.setText(list.get(pos).getAge());
data.height.setText(list.get(pos).getHeight());
data.weight.setText(list.get(pos).getWeight());
data.imc.setText(list.get(pos).getImc());
Toast.makeText(context, "Data deleted", Toast.LENGTH_LONG).show();
);
return convertView;
https://github.com/epilif3sotnas/IMC
【问题讨论】：
尝试删除数据 data = new Data();在 btDel.setOnClickListener 内 在哪一行抛出空指针？ 在我放的代码中，但是在这一行 data.date.setText(list.get(pos).getDate()); 我删除数据 data = new Data();现在它正在工作，谢谢 valentino 【参考方案1】：您正在 onclick 中创建抛出空指针的数据对象。我没有对您的代码进行太多更改，以便您了解代码中发生了什么变化，但是您需要在 if 中初始化这些视图。
package com.example.imc;
import android.annotation.SuppressLint;
import android.content.Context;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.Button;
import android.widget.ListAdapter;
import android.widget.TextView;
import android.widget.Toast;
import androidx.annotation.NonNull;
import com.google.android.gms.tasks.OnFailureListener;
import com.google.android.gms.tasks.OnSuccessListener;
import com.google.firebase.firestore.CollectionReference;
import com.google.firebase.firestore.FirebaseFirestore;
import java.util.ArrayList;
public class CustomAdapterData extends BaseAdapter implements ListAdapter
private ArrayList<objData> list;
private Context context;
private CollectionReference db = FirebaseFirestore.getInstance().collection("user");
private static class Data
TextView date;
TextView age;
TextView height;
TextView weight;
TextView imc;
public CustomAdapterData(ArrayList<objData> list, Context context)
this.list = list;
this.context = context;
@Override
public int getCount()
return list.size();
@Override
public Object getItem(int position)
return list.get(position);
@Override
public long getItemId(int position)
return position;
@SuppressLint("InflateParams")
@Override
public View getView(final int position, View convertView, ViewGroup parent)
final Data data ;
if (convertView == null) // if convertView is null
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = inflater.inflate(R.layout.list_data,
parent, false);
data = new Data();
data.date = convertView.findViewById(R.id.date);
data.age = convertView.findViewById(R.id.age);
data.height = convertView.findViewById(R.id.height);
data.weight = convertView.findViewById(R.id.weight);
data.imc = convertView.findViewById(R.id.imc);
convertView.setTag(data); // set tag on view
else
data = (Data) convertView.getTag();
final objData object = list.get(position);
data.date.setText(object.getDate());
data.age.setText(object.getAge());
data.height.setText(object.getHeight());
data.weight.setText(object.getWeight());
data.imc.setText(object.getImc());
Button btDel = convertView.findViewById(R.id.btDelete);
btDel.setOnClickListener(new View.OnClickListener()
@Override
public void onClick(View v)
//Data data = new Data();
db.document(object.getDate())
.delete()
.addOnSuccessListener(new OnSuccessListener<Void>()
@Override
public void onSuccess(Void aVoid)
Log.d("MainActivity", "DocumentSnapshot successfully deleted!");
Toast.makeText(context, "Data deleted", Toast.LENGTH_LONG).show();
list.remove(position);
notifyDataSetChanged();
)
.addOnFailureListener(new OnFailureListener()
@Override
public void onFailure(@NonNull Exception e)
Log.w("MainActivity", "Error deleting document", e);
Toast.makeText(context, "Data not deleted", Toast.LENGTH_LONG).show();
);
/* data.date.setText(object.getDate());
data.age.setText(object.getAge());
data.height.setText(object.getHeight());
data.weight.setText(object.getWeight());
data.imc.setText(object.getImc());*/
Toast.makeText(context, "Atividade eliminada", Toast.LENGTH_LONG).show();
);
return convertView;
【讨论】：
你只删除了 Data data = new Data();在 btDel 内部？ 还要检查我是如何写的 if else condition for viewholder（在你的情况下是数据） 如果阻塞，findviews 会进入里面 在 if 语句中不需要这行？ LayoutInflater inflater = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);断言充气机！= null;以上是关于我想删除 listView 的数据并出现这个异常 java.lang.NullPointerException的主要内容，如果未能解决你的问题，请参考以下文章
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