setOnCheckChangedListener空指针异常？

如何解决setOnCheckChangedListener空指针异常？

我知道什么是空指针异常。我只是看不到这里有什么问题。复选框将初始化为复选框类型变量，并分配一个视图对象。我想念什么？任何帮助表示赞赏。

2020-08-24 12：32：05.868 22356-22356 /？ E / AndroidRuntime：致命异常：main 流程：com.kittybreath.android.criminalintent2，PID：22356 java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法'void android.widget.CheckBox.setOnCheckedChangeListener（android.widget.CompoundButton $ OnCheckedChangeListener）' 在com.kittybreath.android.criminalintent2.CrimeFragment.onCreateView（CrimeFragment.java:62）

package com.kittybreath.android.criminalintent2;


import android.os.Bundle;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.CompoundButton;
import android.widget.EditText;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;

public class CrimeFragment extends Fragment {
    private Crime crime;
    private EditText titleField;
    private Button dateButton;
    private CheckBox solvedCheckBox;

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        crime = new Crime();
    }

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater,@Nullable ViewGroup container,@Nullable Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.fragment_crime,container,false);
        titleField = v.findViewById(R.id.crime_title);
        dateButton = v.findViewById(R.id.crime_date);
        solvedCheckBox = v.findViewById(R.id.crime_solved);

        titleField.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s,int start,int count,int after) {

            }

            @Override
            public void onTextChanged(CharSequence s,int before,int count) {
                crime.setTitle(s.toString());
            }

            @Override
            public void afterTextChanged(Editable s) {

            }
        });

        dateButton.setText(crime.getDate().toString());
        dateButton.setEnabled(false);

        solvedCheckBox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton buttonView,boolean isChecked) {
                crime.setSolved(isChecked);
            }
        });

        return v;
    }
}

犯罪班

package com.kittybreath.android.criminalintent2;

import java.util.Date;
import java.util.UUID;

public class Crime {
    private UUID id;
    private String title;
    private Date date;
    private boolean solved;

    // Constructor assigns unique id and default current date
    public Crime() {
        id = UUID.randomUUID();
        date = new Date();
    }

    // Getters and Setters
    public UUID getId() {
        return id;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public Date getDate() {
        return date;
    }

    public void setDate(Date date) {
        this.date = date;
    }

    public boolean isSolved() {
        return solved;
    }

    public void setSolved(boolean solved) {
        this.solved = solved;
    }
}

XML代码

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:layout_margin="16dp">

    <TextView
        style="?android:listSeparatorTextViewStyle"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/crime_title_label"/>
    <EditText
        android:id="@+id/crime_title"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="@string/crime_title_hint"/>
    <TextView
        style="?android:listSeparatorTextViewStyle"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/crime_details_label"/>
    <Button
        android:id="@+id/crime_date"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>
    <CheckBox
        android:id="@+id/crime_solved"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/crime_solved_label"/>

</LinearLayout>