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问题：

错误-无法从CursorWindow读取行0，col-1。在从游标访问数据之前，请确保游标已正确初始化--SQLite数据库

陶宏浚
2023-03-14

我看过其他问题，但没有一个答案能满足我的需要。当我点击主活动的回收器视图时，它应该把我带到学生活动，但它没有把我带到学生活动，而是给我显示了这个错误。APK也是构建的，但是在使用应用程序时，错误出现了。

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

import android.annotation.SuppressLint;
import android.content.Intent;
import android.database.Cursor;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageButton;
import android.widget.TextView;

import com.google.android.material.floatingactionbutton.FloatingActionButton;

import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {
    FloatingActionButton fab;
    RecyclerView recyclerView;
    ClassAdapter classAdapter;
    RecyclerView.LayoutManager layoutManager;
    Toolbar toolbar;
    ArrayList<ClassItem> classItems = new ArrayList<>();
    DbHelper dbHelper;


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

        fab = findViewById(R.id.fab_main);
        fab.setOnClickListener(v-> showDialog());
        dbHelper = new DbHelper(this);

        loadClass();

        recyclerView= findViewById(R.id.recyclerView);
        recyclerView.setHasFixedSize(true);
        layoutManager = new LinearLayoutManager(this);
        classAdapter = new ClassAdapter(classItems, this);
        recyclerView.setAdapter(classAdapter);
        recyclerView.setLayoutManager(layoutManager);

        classAdapter.setOnItemClickListener(position -> gotoItemActivity(position));
        setToolbar();


    }

    private void loadClass() {
        Cursor cursor = dbHelper.getClassTable();
        classItems.clear();

        while (cursor.moveToNext()){
            @SuppressLint("Range") int id = cursor.getInt(cursor.getColumnIndex(DbHelper.C_ID));
            @SuppressLint("Range") String className = cursor.getString(cursor.getColumnIndex(DbHelper.CLASS_NAME_KEY));
            @SuppressLint("Range") String subjectName = cursor.getString(cursor.getColumnIndex(DbHelper.SUBJECT_NAME_KEY));
            classItems.add(new ClassItem(id,className,subjectName));
        }
    }

    private void setToolbar() {
        toolbar = findViewById(R.id.toolbar);
        TextView title = toolbar.findViewById(R.id.title_toolbar);
        TextView subtitle = toolbar.findViewById(R.id.subtitle_toolbar);
        ImageButton back = toolbar.findViewById(R.id.back);
        ImageButton save = toolbar.findViewById(R.id.save);

        title.setText("AttendX");
        subtitle.setVisibility(View.GONE);
        back.setVisibility(View.INVISIBLE);
        save.setVisibility(View.INVISIBLE);
    }

    private void gotoItemActivity(int position) {
        Intent intent = new Intent(this, StudentActivity.class);
        intent.putExtra("className",classItems.get(position).getClassName());
        intent.putExtra("subjectName",classItems.get(position).getSubjectName());
        intent.putExtra("position",position);
        intent.putExtra("cid",classItems.get(position).getCid());
        startActivity(intent);
    }

    private void showDialog() {
        MyDialog dialog = new MyDialog();
        dialog.show(getSupportFragmentManager(), MyDialog.CLASS_ADD_DIALOG);
        dialog.setListener((className, subjectName)-> addClass(className, subjectName));

    }

    @SuppressLint("NotifyDataSetChanged")
    private void addClass(String className, String subjectName) {
        long cid = dbHelper.addClass(className,subjectName);
        ClassItem classItem = new ClassItem(cid, className, subjectName);
        classItems.add(classItem);
        classAdapter.notifyDataSetChanged();


    }

    @Override
    public boolean onContextItemSelected(@NonNull MenuItem item) {
        switch (item.getItemId()){
            case 0:
                showUpdateDialog(item.getGroupId());
                break;
            case 1:
                deleteClass(item.getGroupId());
        }
        return super.onContextItemSelected(item);
    }

    private void showUpdateDialog(int position) {
        MyDialog dialog = new MyDialog();
        dialog.show(getSupportFragmentManager(), MyDialog.UPDATE_CLASS_DIALOG);
        dialog.setListener((className,subjectName)->updateClass(position,className,subjectName));
    }

    private void updateClass(int position, String className, String subjectName) {
        dbHelper.updateClass(classItems.get(position).getCid(),className,subjectName);
        classItems.get(position).setClassName(className);
        classItems.get(position).setSubjectName(subjectName);
        classAdapter.notifyItemChanged(position);
    }


    private void deleteClass(int position) {
        dbHelper.deleteClass(classItems.get(position).getCid());
        classItems.remove(position);
        classAdapter.notifyItemRemoved(position);
    }
}

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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=".MainActivity">

    <include
        android:id="@+id/toolbarMain"
        layout="@layout/toolbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <com.google.android.material.floatingactionbutton.FloatingActionButton
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        android:layout_margin="24dp"
        android:id="@+id/fab_main"
        android:src="@drawable/ic_baseline_add_24"
        tools:ignore="ContentDescription" />
    <androidx.recyclerview.widget.RecyclerView
        android:layout_below="@id/toolbarMain"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/recyclerView"/>

</RelativeLayout>

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

import android.annotation.SuppressLint;
import android.content.Intent;
import android.database.Cursor;
import android.os.Bundle;
import android.util.Log;
import android.view.MenuItem;
import android.view.View;
import android.widget.ImageButton;
import android.widget.TextView;

import java.util.ArrayList;

public class StudentActivity extends AppCompatActivity {
    Toolbar toolbar;
    private TextView subtitle;
    private String className;
    private String subjectName;
    private int position;
    private StudentAdapter adapter;
    private RecyclerView recyclerView;
    private ArrayList<StudentItem> studentItems =  new ArrayList<>();
    private RecyclerView.LayoutManager layoutManager;
    private  DbHelper dbHelper;
    private long cid;
    private MyCalendar calendar;


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


        Intent intent = getIntent();
        className = intent.getStringExtra("className");
        subjectName = intent.getStringExtra("subjectName");
        position = intent.getIntExtra("position", -1);
        cid = intent.getLongExtra("cid", -1);
        calendar = new MyCalendar();
        dbHelper = new DbHelper(this);

        setToolbar();
        loadData();


        recyclerView = findViewById(R.id.student_recycler);
        recyclerView.setHasFixedSize(true);
        layoutManager = new LinearLayoutManager(this);
        recyclerView.setLayoutManager(layoutManager);
        adapter = new StudentAdapter(studentItems, this);
        recyclerView.setAdapter(adapter);
        adapter.setOnItemClickListener(position->changeStatus(position));
        loadStatusData();



    }
    private void setToolbar() {
        toolbar = findViewById(R.id.toolbar);

        TextView title = toolbar.findViewById(R.id.title_toolbar);
        subtitle = toolbar.findViewById(R.id.subtitle_toolbar);
        ImageButton back = toolbar.findViewById(R.id.back);
        ImageButton save = toolbar.findViewById(R.id.save);
        save.setOnClickListener(v->saveStatus());

        title.setText(className);

        subtitle.setText(subjectName+" | "+calendar.getDate());


        back.setOnClickListener(v-> onBackPressed());

        toolbar.inflateMenu(R.menu.student_menu);
        toolbar.setOnMenuItemClickListener(menuItem->OnMenuItemClick(menuItem));

    }

    private void saveStatus() {
        for(StudentItem studentItem : studentItems){
            String status = studentItem.getStatus();
            if (status !="P") status = "A";
            long value = dbHelper.addStatus(studentItem.getSid(),cid,calendar.getDate(),status);
            if (value == -1)dbHelper.updateStatus(studentItem.getSid(),calendar.getDate(),status);
        }
    }

    @SuppressLint("NotifyDataSetChanged")
    private void loadStatusData(){
        for(StudentItem studentItem : studentItems){
            String status = dbHelper.getStatus(studentItem.getSid(),calendar.getDate());
            if (status != null) studentItem.setStatus(status);
            else studentItem.setStatus("");
        }
        adapter.notifyDataSetChanged();
    }

    private void loadData() {
        Cursor cursor = dbHelper.getClassTable();
        Log.i("1234567890", "loadData: "+cid);
        studentItems.clear();

        while (cursor.moveToNext()){
            @SuppressLint("Range") long sid = cursor.getInt(cursor.getColumnIndex(DbHelper.S_ID));
            @SuppressLint("Range") int roll = cursor.getInt(cursor.getColumnIndex(DbHelper.STUDENT_ROLL_KEY));
            @SuppressLint("Range") String name = cursor.getString(cursor.getColumnIndex(DbHelper.STUDENT_NAME_KEY));
            studentItems.add(new StudentItem(sid,roll,name));
        }
        cursor.close();

    }

    private void changeStatus(int position) {
        String status = studentItems.get(position).getStatus();
        if (status.equals("P")) status = "A";
        else status ="P";

        studentItems.get(position).setStatus(status);
        adapter.notifyItemChanged(position);
    }

    private boolean OnMenuItemClick(MenuItem menuItem) {
        if (menuItem.getItemId()==R.id.add_student){
            showAddStudentDialog();
        }
        else if (menuItem.getItemId()==R.id.show_Calendar){
            showCalendar();
        }
        else if (menuItem.getItemId()==R.id.show_attendance_sheet){
            openSheetList();
        }
        return true;
    }

    private void openSheetList() {
        long[] idArray = new long[studentItems.size()];
        String[] nameArray = new String[studentItems.size()];
        int[] rollArray = new int[studentItems.size()];

        for (int i = 0; i<idArray.length; i++)
            idArray[i] = studentItems.get(i).getSid();
        for (int i = 0; i<rollArray.length; i++)
            rollArray[i] = studentItems.get(i).getRoll();
        for (int i = 0; i<nameArray.length; i++)
            nameArray[i] = studentItems.get(i).getName();

        Intent intent = new Intent(this, SheetListActivity.class);
        intent.putExtra("cid", cid);
        intent.putExtra("idArray",idArray);
        intent.putExtra("rollArray",rollArray);
        intent.putExtra("nameArray",nameArray);
        startActivity(intent);
    }

    private void showCalendar() {
        MyCalendar calendar = new MyCalendar();
        calendar.show(getSupportFragmentManager(), "");
        calendar.setOnCalendarOkClickListener(this::onCalendarOkClicked);
    }

    private void onCalendarOkClicked(int year, int month, int day) {
        calendar.setDate(year,month,day);
        subtitle.setText(subjectName+" | "+calendar.getDate());
        loadStatusData();
    }

    private void showAddStudentDialog() {
        MyDialog dialog = new MyDialog();
        dialog.show(getSupportFragmentManager(), MyDialog.STUDENT_ADD_DIALOG );
        dialog.setListener((roll, name)-> addStudent(roll, name));
    }

    private void addStudent(String roll_string, String name) {
        int roll = Integer.parseInt(roll_string);
        long sid = dbHelper.addStudent(cid,roll,name);
        StudentItem studentItem = new StudentItem(sid,roll,name);
        studentItems.add(studentItem);
        adapter.notifyDataSetChanged();
    }

    @Override
    public boolean onContextItemSelected(@NonNull MenuItem item) {
        switch (item.getItemId()){
            case 0:
                showUpdateStudentDialog(item.getGroupId());
                break;
            case 1:
                deleteStudent(item.getGroupId());
        }
        return super.onContextItemSelected(item);
    }

    private void showUpdateStudentDialog(int position) {
        MyDialog dialog = new MyDialog(studentItems.get(position).getRoll(),studentItems.get(position).getName());
        dialog.show(getSupportFragmentManager(), MyDialog.UPDATE_STUDENT_DIALOG);
        dialog.setListener((roll_string,name)->updateStudent(position,name));
    }

    private void updateStudent(int position, String name) {
        dbHelper.updateStudent(studentItems.get(position).getSid(),name);
        studentItems.get(position).setName(name);
        adapter.notifyItemChanged(position);
    }

    private void deleteStudent(int position) {
        dbHelper.deleteStudent(studentItems.get(position).getSid());
        studentItems.remove(position);
        adapter.notifyItemRemoved(position);
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
    android:orientation="vertical"
    tools:context=".StudentActivity">


    <include
        android:id="@+id/toolbarStudent"
        layout="@layout/toolbar"/>

    <androidx.recyclerview.widget.RecyclerView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/student_recycler"/>



</LinearLayout>

import android.annotation.SuppressLint;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

import androidx.annotation.Nullable;

class DbHelper extends SQLiteOpenHelper {
    private static final int VERSION = 2;

    //class table
    private static final String CLASS_TABLE_NAME = "CLASS_TABLE";
    public static final String C_ID = "_CID";
    public static final String CLASS_NAME_KEY = "CLASS_NAME";
    public static final String SUBJECT_NAME_KEY = "SUBJECT_NAME";

    private static final String CREATE_CLASS_TABLE =
            "CREATE TABLE " + CLASS_TABLE_NAME + "( " +
                    C_ID + " INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, " +
                    CLASS_NAME_KEY + " TEXT NOT NULL, " +
                    SUBJECT_NAME_KEY + " TEXT NOT NULL, " +
                    "UNIQUE (" + CLASS_NAME_KEY + "," + SUBJECT_NAME_KEY + ")" +
                    ");";

    private static final String DROP_CLASS_TABLE = "DROP TABLE IF EXISTS " + CLASS_TABLE_NAME;
    private static final String SELECT_CLASS_TABLE = "SELECT * FROM " + CLASS_TABLE_NAME;

    //student table

    private static final String STUDENT_TABLE_NAME = "STUDENT_TABLE";
    public static final String S_ID = "_SID";
    public static final String STUDENT_NAME_KEY = "STUDENT_NAME";
    public static final String STUDENT_ROLL_KEY = "ROLL";

    private static final String CREATE_STUDENT_TABLE =
            "CREATE TABLE " + STUDENT_TABLE_NAME +
                    "( " +
                    S_ID + " INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, " +
                    C_ID + " INTEGER NOT NULL, " +
                    STUDENT_NAME_KEY + " TEXT NOT NULL, " +
                    STUDENT_ROLL_KEY + " INTEGER, " +
                    " FOREIGN KEY ( " + C_ID + ") REFERENCES " + CLASS_TABLE_NAME + "(" + C_ID + ")" +
                    ");";

    private static final String DROP_STUDENT_TABLE = "DROP TABLE IF EXISTS " + STUDENT_TABLE_NAME;
    private static final String SELECT_STUDENT_TABLE = "SELECT * FROM " + STUDENT_TABLE_NAME;


    //STATUS TABLE

    private static final String STATUS_TABLE_NAME = "STATUS_TABLE";
    public static final String STATUS_ID = "_STATUS_ID";
    public static final String DATE_KEY = "STATUS_DATE";
    public static final String STATUS_KEY = "STATUS";

    private static final String CREATE_STATUS_TABLE =
            "CREATE TABLE " + STATUS_TABLE_NAME +
                    "(" +
                    STATUS_ID + " INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, " +
                    S_ID + " INTEGER NOT NULL, " +
                    C_ID + " INTEGER NOT NULL, " +
                    DATE_KEY + " DATE NOT NULL, " +
                    STATUS_KEY + " TEXT NOT NULL, " +
                    " UNIQUE (" + S_ID + "," + DATE_KEY + ")," +
                    " FOREIGN KEY (" + S_ID + ") REFERENCES " + STUDENT_TABLE_NAME + "( " + S_ID + ")," +
                    " FOREIGN KEY (" + C_ID + ") REFERENCES " + CLASS_TABLE_NAME + "( " + C_ID + ")" +
                    ");";
    private static final String DROP_STATUS_TABLE = "DROP TABLE IF EXISTS " + STATUS_TABLE_NAME;
    private static final String SELECT_STATUS_TABLE = "SELECT * FROM " + STATUS_TABLE_NAME;


    public DbHelper(@Nullable Context context) {
        super(context, "Attendance.db", null, VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(CREATE_CLASS_TABLE);
        db.execSQL(CREATE_STUDENT_TABLE);
        db.execSQL(CREATE_STATUS_TABLE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        try {
            db.execSQL(DROP_CLASS_TABLE);
            db.execSQL(DROP_STUDENT_TABLE);
            db.execSQL(DROP_STATUS_TABLE);
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    long addClass(String className,String subjectName){
        SQLiteDatabase database = this.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put(CLASS_NAME_KEY,className);
        values.put(SUBJECT_NAME_KEY,subjectName);

        return database.insert(CLASS_TABLE_NAME,null,values);
    }

    Cursor getClassTable(){
        SQLiteDatabase database = this.getReadableDatabase();

        return database.rawQuery(SELECT_CLASS_TABLE,null);
    }

    int deleteClass(long cid){
        SQLiteDatabase database = this.getReadableDatabase();
        return database.delete(CLASS_TABLE_NAME,C_ID+"=?",new String[]{String.valueOf(cid)});
    }

    long updateClass(long cid,String className,String subjectName){
        SQLiteDatabase database = this.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put(CLASS_NAME_KEY,className);
        values.put(SUBJECT_NAME_KEY,subjectName);

        return database.update(CLASS_TABLE_NAME,values,C_ID+"=?",new String[]{String.valueOf(cid)});
    }

    long addStudent(long cid,int roll,String name){
        SQLiteDatabase database = this.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put(C_ID,cid);
        values.put(STUDENT_ROLL_KEY,roll);
        values.put(STUDENT_NAME_KEY,name);
        return database.insert(STUDENT_TABLE_NAME,null,values);
    }

    Cursor getStudentTable(long cid){
        SQLiteDatabase database = this.getReadableDatabase();
        return database.query(STUDENT_TABLE_NAME,null,C_ID+"=?",new String[]{String.valueOf(cid)},null,null,STUDENT_ROLL_KEY);
    }

    int deleteStudent(long sid){
        SQLiteDatabase database = this.getReadableDatabase();
        return database.delete(STUDENT_TABLE_NAME,S_ID+"=?",new String[]{String.valueOf(sid)});
    }

    long updateStudent(long sid,String name){
        SQLiteDatabase database = this.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put(STUDENT_NAME_KEY,name);
        return database.update(STUDENT_TABLE_NAME,values,S_ID+"=?",new String[]{String.valueOf(sid)});
    }

    long addStatus(long sid,long cid,String date,String status){
        SQLiteDatabase database = this.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put(S_ID,sid);
        values.put(C_ID,cid);
        values.put(DATE_KEY,date);
        values.put(STATUS_KEY,status);
        return database.insert(STATUS_TABLE_NAME,null,values);
    }

    long updateStatus(long sid,String date,String status){
        SQLiteDatabase database = this.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put(STATUS_KEY,status);
        String whereClause = DATE_KEY +"='"+date+"' AND "+S_ID+"="+sid;
        return database.update(STATUS_TABLE_NAME,values,whereClause,null);
    }

    @SuppressLint("Range")
    String getStatus(long sid, String date){
        String status=null;
        SQLiteDatabase database = this.getReadableDatabase();
        String whereClause = DATE_KEY +"='"+date+"' AND "+S_ID+"="+sid;
        Cursor cursor = database.query(STATUS_TABLE_NAME,null,whereClause,null,null,null,null);
        if(cursor.moveToFirst())
            status = cursor.getString(cursor.getColumnIndex(STATUS_KEY));
        return status;
    }

    Cursor getDistinctMonths(long cid){
        SQLiteDatabase database = this.getReadableDatabase();
        return database.query(STATUS_TABLE_NAME,new String[]{DATE_KEY},C_ID+"="+cid,null,"substr("+DATE_KEY+",4,7)",null,null);//01.04.2020
    }
}

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.manage.attendx/com.manage.attendx.StudentActivity}: java.lang.IllegalStateException: Couldn't read row 0, col -1 from CursorWindow.  Make sure the Cursor is initialized correctly before accessing data from it.
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3308)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3457)
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2044)
    at android.os.Handler.dispatchMessage(Handler.java:107)
    at android.os.Looper.loop(Looper.java:224)
    at android.app.ActivityThread.main(ActivityThread.java:7562)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:539)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950)
Caused by: java.lang.IllegalStateException: Couldn't read row 0, col -1 from CursorWindow.  Make sure the Cursor is initialized correctly before accessing data from it.
    at android.database.CursorWindow.nativeGetLong(Native Method)
    at android.database.CursorWindow.getLong(CursorWindow.java:542)
    at android.database.CursorWindow.getInt(CursorWindow.java:609)
    at android.database.AbstractWindowedCursor.getInt(AbstractWindowedCursor.java:71)
    at com.manage.attendx.StudentActivity.loadData(StudentActivity.java:112)
    at com.manage.attendx.StudentActivity.onCreate(StudentActivity.java:51)
    at android.app.Activity.performCreate(Activity.java:7893)
    at android.app.Activity.performCreate(Activity.java:7880)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1307)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3283)
    ... 11 more

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.manage.attendx">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.AttendX">
        <activity
            android:name=".SheetActivity"
            android:exported="true" />
        <activity
            android:name=".SheetListActivity"
            android:exported="true" />
        <activity
            android:name=".StudentActivity"
            android:exported="true" />
        <activity
            android:name=".MainActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

谁能帮我解决这个问题吗？

共有1个答案

卢深
2023-03-14

发行

你的问题是：-

private void loadData() {
        Cursor cursor = dbHelper.getClassTable();
        Log.i("1234567890", "loadData: "+cid);
        studentItems.clear();

        while (cursor.moveToNext()){
            @SuppressLint("Range") long sid = cursor.getInt(cursor.getColumnIndex(DbHelper.S_ID));
            @SuppressLint("Range") int roll = cursor.getInt(cursor.getColumnIndex(DbHelper.STUDENT_ROLL_KEY));
            @SuppressLint("Range") String name = cursor.getString(cursor.getColumnIndex(DbHelper.STUDENT_NAME_KEY));
            studentItems.add(new StudentItem(sid,roll,name));
        }
        cursor.close();

    }

解释

    null
    null

修复

您要么希望从Class表中获取适当的列(C_ID、CLASS_NAME_KEY和SUBJECT_NAME)，要么将Student表用作检索用于获取光标的数据的表。

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