Ошибка: невозможно разрешить символ «@style/Theme.Androidstudio» в AndroidManifest.xml для Kotlin Android Development

Обратитесь к решению ниже. Я также предоставил пошаговую процедуру реализации операций CRUD в Kotlin:

CRUD ОПЕРАЦИЯ С SQLITE

Перейдите в AndroidManifest.xml.

добавить эти разрешения -

<uses-permission android:name = "android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name = "android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name = "android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name = "android.permission.INTERNET" />

под тегом и над тегом

как здесь

<?xml version = "1.0" encoding = "utf-8"?>
<manifest xmlns:android = "http://schemas.android.com/apk/res/android"
    xmlns:tools = "http://schemas.android.com/tools">
    <uses-permission android:name = "android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name = "android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name = "android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name = "android.permission.INTERNET" />
    <application
        android:allowBackup = "true"
        android:dataExtractionRules = "@xml/data_extraction_rules"
        android:fullBackupContent = "@xml/backup_rules"
        android:icon = "@mipmap/ic_launcher"
        android:label = "@string/app_name"
        android:supportsRtl = "true"
        android:theme = "@style/Theme.Androidstudio"
        tools:targetApi = "31">
        <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>

}

После class MainActivity : AppCompatActivity() {

добавьте эту строку

private lateinit var db:SQLiteDatabase

после setContentView(R.layout.activity_main)

добавьте эту строку

 db = openOrCreateDatabase("employeemanager.db", MODE_PRIVATE,null)

Создание таблицы

val createTableQuery = "CREATE TABLE IF NOT EXISTS employee(employeeid INT PRIMARY KEY, name TEXT, phonenumber INT, country TEXT)"
        db?.execSQL(createTableQuery)

Вставка в таблицу

 val insertQuery = "INSERT INTO employee VALUES("+idtext+",'"+nametext+"',"+phonenumber+",'"+country+"')"
                db?.execSQL(insertQuery)
                Toast.makeText(this@MainActivity, "Inserted Data Successfully!",Toast.LENGTH_SHORT).show()

Добавление извлеченных данных в счетчик

val fetchdata = "SELECT DISTINCT country FROM employee"
        val cursor = db?.rawQuery(fetchdata,null)
        val countries = ArrayList<String>()
        while(cursor!!.moveToNext()) {
            val country1 = cursor.getString(0)
            countries.add(country1)
        }
        cursor?.close()
        var spinner = findViewById<Spinner>(R.id.spinner)
        val spinneradapter = ArrayAdapter<String>(this,android.R.layout.simple_spinner_dropdown_item,countries)
        spinneradapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item)
        spinner.adapter = spinneradapter
        spinner.onItemSelectedListener = object : OnItemSelectedListener {
            override fun onItemSelected(parent: AdapterView<*>, view: View, position: Int, id: Long) {
                selectedItem = parent.getItemAtPosition(position).toString();
                Toast.makeText(this@SecondActivity, "$selectedItem",Toast.LENGTH_SHORT).show()

            }
            override fun onNothingSelected(parent: AdapterView<*>) {
            }
        }

Выбор данных и их отображение

 search.setOnClickListener {
            val searchcountrydata = "SELECT * FROM employee WHERE country  = " +"'$selectedItem'";
            val cursor2 = db?.rawQuery(searchcountrydata,null)
            val displayString = StringBuilder()
            while(cursor2!!.moveToNext()) {
                val id = cursor2.getString(0)
                val name = cursor2.getString(1)
                val phonenumber = cursor2.getString(2)
                val country = cursor2.getString(3)
                displayString.append("ID: $id, Name: $name, PhoneNumber: $phonenumber, Country: $country" +"\n")
            }
            display2.text = displayString.toString()
        }

Сортировка данных

sort.setOnClickListener {
            val newquery = "SELECT * FROM employee ORDER BY employeeid DESC"
            val cursor3 = db?.rawQuery(newquery,null)
            val displayString2 = StringBuilder()
            while(cursor3!!.moveToNext()) {
                val id = cursor3.getString(0)
                val name = cursor3.getString(1)
                val phonenumber = cursor3.getString(2)
                val country = cursor3.getString(3)
                displayString2.append("ID: $id, Name: $name, PhoneNumber: $phonenumber, Country: $country" +"\n")
            }
            display2.text = displayString2.toString()
        }

Обновление данных

updatebutton.setOnClickListener {
            val empval = empid.text.toString()
            val countryval = country.text.toString()
            val updatequery = "UPDATE employee SET country  = " + "'$countryval'"+" WHERE employeeid = $empval"
            db?.execSQL(updatequery)
            Toast.makeText(this@ThirdActivity, "Updated Successfully",Toast.LENGTH_SHORT).show()

        }

УДАЛЕНИЕ ДАННЫХ

delete.setOnClickListener {
        val rollval = rollno.text.toString();
        val deletequery = "DELETE FROM STUDENT WHERE ROLLNO=$rollval";
        db?.execSQL(deletequery)
        Toast.makeText(this@MainActivity,"Deleted Data Successfully!",Toast.LENGTH_SHORT).show()
    }

НАЙДЕНИЕ максимума и минимума в данных

   maxandmin.setOnClickListener {
 val selectquery1  = "SELECT productid, name, price FROM PRODUCTS p WHERE p.price IN (SELECT MAX(price) FROM PRODUCTS)"
        val selectquery2 = "SELECT productid, name, price FROM PRODUCTS p WHERE p.price IN (SELECT MIN(price) FROM PRODUCTS)"
        val cursor1 = db?.rawQuery(selectquery1, null)
        val cursor2 = db?.rawQuery(selectquery2, null)
        val str = StringBuilder()
        str.append("Maximum Priced Product Details: \n")
        while(cursor1!!.moveToNext()) {
            val id = cursor1.getString(0)
            val name = cursor1.getString(1)
            val price = cursor1.getString(2)
            str.append("Product ID: $id, Product Name: $name, Product Price: $price")
        }
        str.append("\n\nMinimum Priced Product Details: \n")
        while(cursor2!!.moveToNext()) {
            val id = cursor2.getString(0)
            val name = cursor2.getString(1)
            val price = cursor2.getString(2)
            str.append("Product ID: $id, Product Name: $name, Product Price: $price")
        }

Нахождение общего количества

str.append("\n\nTotal No Of Products: ")
            val findtotproducts = "SELECT COUNT(*) FROM PRODUCTS"
            val totprice = "SELECT SUM(PRICE) FROM PRODUCTS"
            val cursor4 = db?.rawQuery(findtotproducts,null)
            val cursor5 = db?.rawQuery(totprice, null)

            while(cursor4!!.moveToNext()) {
                val countprod = cursor4.getString(0)
                str.append(countprod)
            }

Нахождение общей цены

     str.append("\n\nTotal Price of Products: ")
        while(cursor5!!.moveToNext()) {
            val countprod2 = cursor5.getString(0)
            str.append(countprod2)
        }
        display.text = str;

Ниже я написал полный процесс реализации операций CRUD. Я объяснил это с помощью listview

БАЗА ДАННЫХ

Перейдите в AndroidManifest.xml.

добавить эти разрешения -

    <uses-permission android:name = "android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name = "android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name = "android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name = "android.permission.INTERNET" />

below <manifest> tag and above <application> tag

like here 

<?xml version = "1.0" encoding = "utf-8"?>
<manifest xmlns:android = "http://schemas.android.com/apk/res/android"
    xmlns:tools = "http://schemas.android.com/tools">
    <uses-permission android:name = "android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name = "android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name = "android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name = "android.permission.INTERNET" />
    <application
        android:allowBackup = "true"
        android:dataExtractionRules = "@xml/data_extraction_rules"
        android:fullBackupContent = "@xml/backup_rules"
        android:icon = "@mipmap/ic_launcher"
        android:label = "@string/app_name"
        android:supportsRtl = "true"
        android:theme = "@style/Theme.Androidstudio"
        tools:targetApi = "31">
        <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>

Создайте новый класс DatabaseHelper и добавьте код ниже:

import android.content.ContentValues
import android.content.Context
import android.database.Cursor
import android.database.sqlite.SQLiteDatabase
import android.database.sqlite.SQLiteOpenHelper

class DatabaseHelper(context: Context) : SQLiteOpenHelper(context, DATABASE_NAME, null, DATABASE_VERSION) {

    companion object {
        private const val DATABASE_VERSION = 1
        private const val DATABASE_NAME = "StudentManager.db"

        // Table name and columns
        private const val TABLE_NAME = "students"
        private const val COLUMN_ROLL_NUMBER = "roll_number"
        private const val COLUMN_NAME = "name"
        private const val COLUMN_MARKS = "marks"
    }

    override fun onCreate(db: SQLiteDatabase?) {
        val createTableQuery = "CREATE TABLE $TABLE_NAME (" +
                "$COLUMN_ROLL_NUMBER TEXT PRIMARY KEY," +
                "$COLUMN_NAME TEXT," +
                "$COLUMN_MARKS INTEGER)"
        db?.execSQL(createTableQuery)
    }

    override fun onUpgrade(db: SQLiteDatabase?, oldVersion: Int, newVersion: Int) {
        db?.execSQL("DROP TABLE IF EXISTS $TABLE_NAME")
        onCreate(db)
    }

    fun addStudent(rollNumber: String, name: String, marks: Int): Boolean {
        val db = this.writableDatabase
        val contentValues = ContentValues()
        contentValues.put(COLUMN_ROLL_NUMBER, rollNumber)
        contentValues.put(COLUMN_NAME, name)
        contentValues.put(COLUMN_MARKS, marks)
        val result = db.insert(TABLE_NAME, null, contentValues)
        return result != -1L
    }

    fun readAllStudents(): Cursor {
        val db = this.readableDatabase
        return db.rawQuery("SELECT * FROM $TABLE_NAME", null)
    }

    fun updateStudent(rollNumber: String, name: String, marks: Int): Boolean {
        val db = this.writableDatabase
        val contentValues = ContentValues()
        contentValues.put(COLUMN_NAME, name)
        contentValues.put(COLUMN_MARKS, marks)
        val result = db.update(TABLE_NAME, contentValues, "$COLUMN_ROLL_NUMBER = ?", arrayOf(rollNumber))
        return result != -1
    }

    fun deleteStudent(rollNumber: String): Boolean {
        val db = this.writableDatabase
        val result = db.delete(TABLE_NAME, "$COLUMN_ROLL_NUMBER = ?", arrayOf(rollNumber))
        return result != -1
    }
}


In the Main Activity

do this 


package com.example.androidstudio
import DatabaseHelper
import android.content.Context
import android.database.Cursor
import android.os.Bundle
import android.widget.Button
import android.widget.EditText
import android.widget.Toast
import androidx.appcompat.app.AlertDialog
import androidx.appcompat.app.AppCompatActivity

class MainActivity : AppCompatActivity() {
    fun showAlert(context: Context, title: String, message: String) {
        val builder = AlertDialog.Builder(context)
        builder.setTitle(title)
        builder.setMessage(message)

        builder.setPositiveButton("OK") { dialog, _ ->
            dialog.dismiss()
        }
        val dialog = builder.create()
        dialog.show()
    }
    private lateinit var databaseHelper: DatabaseHelper

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        databaseHelper = DatabaseHelper(this)

        val rollNumberEditText = findViewById<EditText>(R.id.rollNumberEditText)
        val nameEditText = findViewById<EditText>(R.id.nameEditText)
        val marksEditText = findViewById<EditText>(R.id.marksEditText)
        val addButton = findViewById<Button>(R.id.addButton)
        val displayButton = findViewById<Button>(R.id.displayButton)
        val updatestudent = findViewById<Button>(R.id.updatestudent)
        val deletestudent = findViewById<Button>(R.id.deletestudent)
        updatestudent.setOnClickListener {
            val rollNumber = rollNumberEditText.text.toString()
            val name = nameEditText.text.toString()
            val marks = marksEditText.text.toString()

            if (rollNumber.isNotEmpty() && name.isNotEmpty() && marks.isNotEmpty()) {
                if (databaseHelper.updateStudent(rollNumber, name, marks.toInt())) {
                    Toast.makeText(this, "Updated Student Successfully", Toast.LENGTH_SHORT).show()
                } else {
                    Toast.makeText(this, "Failed to update student", Toast.LENGTH_SHORT).show()
                }
            } else {
                Toast.makeText(this, "Please fill in all fields", Toast.LENGTH_SHORT).show()
            }

        }

        deletestudent.setOnClickListener {
            val rollNumber = rollNumberEditText.text.toString()

            if (rollNumber.isNotEmpty()) {
                if (databaseHelper.deleteStudent(rollNumber)) {
                    Toast.makeText(this, "Deleted Student Successfully", Toast.LENGTH_SHORT).show()
                } else {
                    Toast.makeText(this, "Failed to delete student", Toast.LENGTH_SHORT).show()
                }
            } else {
                Toast.makeText(this, "Please fill in roll number field", Toast.LENGTH_SHORT).show()
            }
        }
        addButton.setOnClickListener {
            val rollNumber = rollNumberEditText.text.toString()
            val name = nameEditText.text.toString()
            val marks = marksEditText.text.toString()

            if (rollNumber.isNotEmpty() && name.isNotEmpty() && marks.isNotEmpty()) {
                if (databaseHelper.addStudent(rollNumber, name, marks.toInt())) {
                    Toast.makeText(this, "Student added successfully", Toast.LENGTH_SHORT).show()
                } else {
                    Toast.makeText(this, "Failed to add student", Toast.LENGTH_SHORT).show()
                }
            } else {
                Toast.makeText(this, "Please fill in all fields", Toast.LENGTH_SHORT).show()
            }
        }

        displayButton.setOnClickListener {
            val cursor: Cursor = databaseHelper.readAllStudents()
            if (cursor.count == 0) {
                Toast.makeText(this, "No students to display", Toast.LENGTH_SHORT).show()
                return@setOnClickListener
            }
            val displayString = StringBuilder()
            while (cursor.moveToNext()) {
                val rollNumber = cursor.getString(0)
                val name = cursor.getString(1)
                val marks = cursor.getInt(2)
                displayString.append("Roll Number: $rollNumber, Name: $name, Marks: $marks\n")
            }
            showAlert(this,"Selected Items", displayString.toString())
        }
    }

    override fun onDestroy() {
        databaseHelper.close()
        super.onDestroy()
    }
}

ПОИСК КОНКРЕТНОГО ВХОДА

displayButton.setOnClickListener {
        val name2 = nameEditText.text.toString()
           val cursor2: Cursor = databaseHelper.findtotstudents(name2)
            if (cursor2.count == 0) {
                Toast.makeText(this, "No students to display", Toast.LENGTH_SHORT).show()
                return@setOnClickListener
            }
            val displayString2 = StringBuilder()
            while (cursor2.moveToNext()) {
                val count = cursor2.getString(0)
                displayString2.append("Count is $count")
            }
            showAlert(this,"Count Items", displayString2.toString())
        }
    }

FUNCTION IN databaseHelper is 

fun findtotstudents(name: String): Cursor {
        val db = this.readableDatabase
        return db.rawQuery("SELECT COUNT(roll_number) FROM $TABLE_NAME WHERE name= + \"$name\"", null)
    }

ВЫБОР СЧЕТА РОЛИКОВ С ПОХОЖИМИ НАЗВАНИЯМИ

MainActivity.kt

displayButton.setOnClickListener {
 
val cursor2: Cursor = databaseHelper.checkeachcount()
            if (cursor2.count == 0) {
                Toast.makeText(this, "No students to display", Toast.LENGTH_SHORT).show()
                return@setOnClickListener
            }
            val displayString2 = StringBuilder()
            while (cursor2.moveToNext()) {
                val count = cursor2.getString(1)
                val name = cursor2.getString(0)
                displayString2.append("Name : $name, Count: $count")
            }
            showAlert(this,"Name and Count", displayString2.toString())
        }

DatabaseHelper

    fun checkeachcount(): Cursor {
        val db = this.readableDatabase
        return db.rawQuery("SELECT name, COUNT(roll_number) FROM $TABLE_NAME GROUP BY name", null)
    }

ВЫБОР ИМЯ И ОТЧЕТ СТУДЕНТА С НАИБОЛЬШИМИ ОТМЕТКАМИ И СТУДЕНТА С НАИБОЛЬШИМИ ОТМЕТКАМИ

База данныхПомощник

    fun findmaxstudent(): Cursor {
        val db = this.readableDatabase
        return db.rawQuery("SELECT name, marks FROM $TABLE_NAME a WHERE a.marks = (SELECT MAX(MARKS) FROM $TABLE_NAME)",null)
    }

    fun findminstudent(): Cursor {
        val db = this.readableDatabase
        return db.rawQuery("SELECT name, marks FROM $TABLE_NAME a WHERE a.marks = (SELECT MIN(MARKS) FROM $TABLE_NAME)",null)
    }

MainActivity 

 displayButton.setOnClickListener {


            val cursor2: Cursor = databaseHelper.findmaxstudent()
            if (cursor2.count == 0) {
                Toast.makeText(this, "No students to display", Toast.LENGTH_SHORT).show()
                return@setOnClickListener
            }
            val displayString2 = StringBuilder()
            while (cursor2.moveToNext()) {
                val maxmarks = cursor2.getString(1)
                val name = cursor2.getString(0)
                displayString2.append("Name : $name, Max Marks: $maxmarks\n")
            }
            val cursor: Cursor = databaseHelper.findminstudent()
            if (cursor.count == 0) {
                Toast.makeText(this, "No students to display", Toast.LENGTH_SHORT).show()
                return@setOnClickListener
            }
            while (cursor.moveToNext()) {
                val minmarks = cursor.getString(1)
                val name = cursor.getString(0)
                displayString2.append("Name : $name, Min Marks: $minmarks\n")
            }
            showAlert(this,"Name and Count", displayString2.toString())
        }

ОТОБРАЖЕНИЕ БАЗЫ ДАННЫХ В LISTVIEW

displayall.setOnClickListener {
            var arr = emptyArray<String>()
            val cursor: Cursor = databaseHelper.readAllStudents()
            if (cursor.count == 0) {
                Toast.makeText(this, "No students to display", Toast.LENGTH_SHORT).show()
                return@setOnClickListener
            }
            while (cursor.moveToNext()) {
                val rollNumber = cursor.getString(0)
                val name = cursor.getString(1)
                val marks = cursor.getInt(2)
                arr+= rollNumber + "  "+name+"  "+marks
            }
            var adapter = ArrayAdapter(this,android.R.layout.simple_list_item_1,arr)
            ls.adapter = adapter

        }

ДОБАВЛЕНИЕ ЗНАЧЕНИЙ В SPINNER ИЗ БД

 var spinner = findViewById<Spinner>(R.id.spinner)
        var ls = findViewById<ListView>(R.id.ls)
        var arr = emptyArray<String>()
        val cursor: Cursor = databaseHelper.getcountries()
        if (cursor.count == 0) {
            Toast.makeText(this, "Nothing to display", Toast.LENGTH_SHORT).show()
        }
        while (cursor.moveToNext()) {
            val countrytemp = cursor.getString(0)
            arr+= countrytemp
        }
        var adapter = ArrayAdapter(this,android.R.layout.simple_list_item_1,arr)
        spinner.adapter = adapter
        var selectedItem = ""
        spinner.onItemSelectedListener = object : AdapterView.OnItemSelectedListener {
            override fun onItemSelected(
                parent: AdapterView<*>?,
                view: View?,
                position: Int,
                id: Long
            ) {
                selectedItem = parent?.getItemAtPosition(position).toString()
                Toast.makeText(this@SecondActivity, selectedItem, Toast.LENGTH_SHORT).show()
            }

            override fun onNothingSelected(parent: AdapterView<*>?) {
                TODO("Not yet implemented")
            }
        }

Ознакомьтесь с этим ответом для получения помощи по счетчику: Код Kotlin сообщает: «Ни одна из следующих функций не может быть вызвана с предоставленными аргументами»

база данных

введите код сюда

package com.example.labp;

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

public class databasehelper extends SQLiteOpenHelper {

    private static final String DB_NAME = "student";

    // below int is our database version
    private static final int DB_VERSION = 1;

    // below variable is for our table name.
    private static final String TABLE_NAME = "students";

    // below variable is for our id column.
    private static final String Stud_id = "stud_id";

    // below variable is for our course name column
    private static final String NAME_COL = "name";
    private static final String Marks = "marks";

    // below variable id for our course duration column.


    // creating a constructor for our database handler.
    public databasehelper(Context context) {
        super(context, DB_NAME, null, DB_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String query = "CREATE TABLE " + TABLE_NAME + " ("
                + Stud_id + " INTEGER PRIMARY KEY, "
                + NAME_COL + " TEXT,"
                + Marks + " INTEGER)";
        db.execSQL(query);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
        onCreate(db);
    }

    public void addNewStudent(int roll_no, String name, int marks) {
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues values = new ContentValues();

        values.put(Stud_id,roll_no);
        values.put(NAME_COL, name);
        values.put(Marks,marks);
        db.insert(TABLE_NAME, null, values);
        db.close();
    }

    public String display(){
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor cur = db.rawQuery("Select * from " + TABLE_NAME,null);
        StringBuilder stringBuilder = new StringBuilder();
        while(cur.moveToNext()){
            int roll_no = cur.getInt(0);
            String name = cur.getString(1);;
            int marks = cur.getInt(2);

            stringBuilder.append("Roll No: ").append(roll_no)
                    .append(", Name: ").append(name)
                    .append(", Marks: ").append(marks)
                    .append("\n");
        }
        return stringBuilder.toString();
    }
}

main java

package com.example.labp;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    private EditText rollno,name1,marks;
    private TextView tv;
    private Button btn,disp;

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

        rollno = findViewById(R.id.editTextText);
        name1 = findViewById(R.id.editTextText2);
        marks = findViewById(R.id.editTextText3);

        btn = findViewById(R.id.button);
        disp = findViewById(R.id.button2);
        db = new databasehelper(MainActivity.this);
        tv = findViewById(R.id.textView2);
        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String roll_no_txt = rollno.getText().toString();
                int roll_no = Integer.parseInt(roll_no_txt);
                String name = name1.getText().toString();
                String marks_no_txt = marks.getText().toString();
                int mrks = Integer.parseInt(marks_no_txt);

                db.addNewStudent(roll_no,name,mrks);

                Toast.makeText(MainActivity.this, "Student has been added.", Toast.LENGTH_SHORT).show();
            }
        });
        disp.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String studentData = db.display();
                tv.setText(studentData);
            }
        });
    }
}

Возможно, попробуйте добавить это в свой код.

val intent= Intent(this,thirda::class.java)
            intent.putExtra("score",cnt)
            startActivity(intent)
val score = intent.getIntExtra("score", 0)

Основная деятельность:

package com.example.dbhelper;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import java.util.concurrent.Callable;

public class MainActivity extends AppCompatActivity {

    private EditText CourseName, CourseTracks, CourseDuration,CourseDescription  ;
    private Button submit;
    private DBHandler dbHandler;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        CourseName = findViewById(R.id.editTextText);
        CourseTracks = findViewById(R.id.editTextText2);
        CourseDuration = findViewById(R.id.editTextText3);
        CourseDescription = findViewById(R.id.editTextText4);
        submit = findViewById(R.id.submit);
        dbHandler = new DBHandler(MainActivity.this);
        submit.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                // below line is to get data from all edit text fields.
                String courseName = CourseName.getText().toString();
                String courseTracks = CourseTracks.getText().toString();
                String courseDuration = CourseDuration.getText().toString();
                String courseDescription = CourseDescription.getText().toString();

                // validating if the text fields are empty or not.
                if (courseName.isEmpty() && courseTracks.isEmpty() && courseDuration.isEmpty() && courseDescription.isEmpty()) {
                    Toast.makeText(MainActivity.this, "Please enter all the data..", Toast.LENGTH_SHORT).show();
                    return;
                }

                dbHandler.addNewCourse(courseName, courseDuration, courseDescription, courseTracks);

                // after adding the data we are displaying a toast message.
                Toast.makeText(MainActivity.this, "Course has been added.", Toast.LENGTH_SHORT).show();
                CourseName.setText("");
                CourseDuration.setText("");
                CourseTracks.setText("");
                CourseDescription.setText("");

                Intent intent = new Intent(MainActivity.this,MainActivity2.class);
                startActivity(intent);
            }
        });
    }
}

ДБХЕЛПЕР.JAVA:

package com.example.dbhelper;
import android.content.ContentValues;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class DBHandler extends SQLiteOpenHelper {
    private static final String DB_NAME = "coursedb";

    // below int is our database version
    private static final int DB_VERSION = 1;

    // below variable is for our table name.
    private static final String TABLE_NAME = "mycourses";

    // below variable is for our id column.
    private static final String ID_COL = "id";

    // below variable is for our course name column
    private static final String NAME_COL = "name";

    // below variable id for our course duration column.
    private static final String DURATION_COL = "duration";

    // below variable for our course description column.
    private static final String DESCRIPTION_COL = "description";

    // below variable is for our course tracks column.
    private static final String TRACKS_COL = "tracks";

    // creating a constructor for our database handler.
    public DBHandler(Context context) {
        super(context, DB_NAME, null, DB_VERSION);
    }
    @Override
    public void onCreate(SQLiteDatabase db) {
        String query = "CREATE TABLE " + TABLE_NAME + " ("
                + ID_COL + " INTEGER PRIMARY KEY, "
                + NAME_COL + " TEXT,"
                + DURATION_COL + " TEXT,"
                + DESCRIPTION_COL + " TEXT,"
                + TRACKS_COL + " TEXT)";

        // at last we are calling a exec sql
        // method to execute above sql query
        db.execSQL(query);
    }
    public void addNewCourse(String courseName, String courseDuration, String courseDescription, String courseTracks) {
    SQLiteDatabase db = this.getWritableDatabase();
    ContentValues values = new ContentValues();
    values.put(NAME_COL, courseName);
        values.put(DURATION_COL, courseDuration);
        values.put(DESCRIPTION_COL, courseDescription);
        values.put(TRACKS_COL, courseTracks);

    // after adding all values we are passing
    // content values to our table.
        db.insert(TABLE_NAME, null, values);

    // at last we are closing our
    // database after adding database.
        db.close();
}




    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
        onCreate(db);
    }
}

ОСНОВНОЙ АКТ 2:

пакет com.example.dbhelper;

импортировать androidx.appcompat.app.AppCompatActivity;

импортировать android.os.Bundle;

публичный класс MainActivity2 расширяет AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main2);
}

}