按钮在空对象引用上抛出 (android.view.View$OnClickListener)'

问题描述 投票：0回答：1

我需要更新 ListAdapter 中的日期，为此我显示一个由 

dialog
和 
2 EditTexts
组成的 
1 Button
，这里的问题是，当我单击对话框中的“更新”按钮时，它会抛出

(android.view.View$OnClickListener)' on a null object reference

顺便说一句，我使用 firebase 实时数据库来保存数据。

堆栈跟踪：

java.lang.NullPointerException：尝试调用虚拟方法“void” android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' 在空对象引用上 在 com.example.notasderober.ReadNotes.showUpdateDialog(ReadNotes.java:106) 在 com.example.notasderober.ReadNotes.access$000(ReadNotes.java:33) 在 com.example.notasderober.ReadNotes$2.onItemClick(ReadNotes.java:77) 在 android.widget.AdapterView.performItemClick(AdapterView.java:330) 在 android.widget.AbsListView.performItemClick(AbsListView.java:1187) 在 android.widget.AbsListView$PerformClick.run(AbsListView.java:3179) 在 android.widget.AbsListView$3.run(AbsListView.java:4097) 在 android.os.Handler.handleCallback(Handler.java:938) 在 android.os.Handler.dispatchMessage(Handler.java:99) 在 android.os.Looper.loop(Looper.java:223) 在 android.app.ActivityThread.main(ActivityThread.java:7656) 在 java.lang.reflect.Method.invoke（本机方法） 在 com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592) 在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)

代码：

package com.example.notasderober;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.Toast;

import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;
import com.google.firebase.firestore.auth.User;

import org.checkerframework.checker.units.qual.A;

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

public class ReadNotes extends AppCompatActivity {


   List<Users> notesList;

    ListView listView;
    Button updateButton;
     View updateDialogView;
      LayoutInflater inflater;

    DatabaseReference studentDbRef;




    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_read_notes);
        listView = findViewById(R.id.listview);
        notesList = new ArrayList<>();
        inflater = getLayoutInflater();    
         updateDialogView = inflater.inflate(R.layout.update_dialog,null);
       updateButton  = updateDialogView.findViewById(R.id.updateNoteButton);

        studentDbRef =FirebaseDatabase.getInstance().getReference("Notas");

        studentDbRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
                notesList.clear();
                for (DataSnapshot studentDatasnap : snapshot.getChildren()){
                    Users notes = studentDatasnap.getValue(Users.class);
                    notesList.add(notes);
                }
                ListAdapter adapter = new ListAdapter(ReadNotes.this,notesList);
                listView.setAdapter(adapter);
            }

            @Override
            public void onCancelled(@NonNull DatabaseError error) {

            }
        });

     listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
         @Override
         public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
             Users students = notesList.get(i);
             showUpdateDialog(students.getId(), students.getName());

         }
     });
    }





    //SHOW UPDATE DIALOG

    private void showUpdateDialog (final String id, String name) {

        Log.d("updateDialog","Dialog update");
        final AlertDialog.Builder updateDialog = new AlertDialog.Builder(this);



        updateDialog.setView(updateDialogView);

       final  EditText updateNote = findViewById(R.id.updateNoteText);
       final EditText updateNoteContent = findViewById(R.id.updateContentText);



        updateDialog.setTitle("Actualizando : " + name);
        final AlertDialog alertDialog = updateDialog.create();
        alertDialog.show();

       updateButton.setOnClickListener(new View.OnClickListener() { // maybe here is the problem
            @Override
            public void onClick(View view) {

                String noteTitle = updateNote.getText().toString();
                String noteContent = updateNoteContent.getText().toString();

                updateData(id,noteTitle,noteContent);

                Toast.makeText(ReadNotes.this,"Nota actualizada",Toast.LENGTH_SHORT).show();

            }
        });
    }



    //UPDATE DATA IN DATABASE
    private void updateData (String id, String name, String note) {
        DatabaseReference dbRef = FirebaseDatabase.getInstance().getReference("Notas").child(id);
        Users noteEx = new Users(id,name,note);
        dbRef.setValue(noteEx);
    }

XML 文件：

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".ReadNotes">

    <TextView
        android:id="@+id/textView5"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Saved notes"
        android:textSize="34sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.497"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.023" />

    <ListView
        android:id="@+id/listview"
        android:layout_width="409dp"
        android:layout_height="668dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.968" />

</androidx.constraintlayout.widget.ConstraintLayout>

XML 对话框文件：

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <EditText
        android:id="@+id/updateNoteText"
        android:layout_width="289dp"
        android:layout_height="144dp"
        android:ems="10"
        android:hint="Nota"
        android:inputType="text"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.368"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.054" />

    <EditText
        android:id="@+id/updateContentText"
        android:layout_width="286dp"
        android:layout_height="127dp"
        android:ems="10"
        android:hint="Contenido nota"
        android:inputType="text"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.381"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.462" />

    <Button
        android:id="@+id/updateNoteButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Modificar"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.976" />
</androidx.constraintlayout.widget.ConstraintLayout>

我尝试检查按钮是否在 xml 文件中正确声明，并且也作为常量字段，但错误仍然存在。

java android listadapter
1个回答
0
投票

使用recyclerview代替ListView

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