SQLite Implementation Kotlin

AndroidManifest.xml

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

    <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:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.MySQL_Lite"
        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>

build.gradle

plugins {
    id 'com.android.application'
    id 'kotlin-android'
    id 'kotlin-android-extensions'
}

android {
    compileSdk 32

    defaultConfig {
        applicationId "com.example.mysql_lite"
        minSdk 21
        targetSdk 32
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
    kotlinOptions {
        jvmTarget = '1.8'
    }
}

dependencies {

    implementation 'androidx.core:core-ktx:1.7.0'
    implementation 'androidx.appcompat:appcompat:1.4.2'
    implementation 'com.google.android.material:material:1.6.1'
    implementation 'androidx.constraintlayout:constraintlayout:2.1.4'
    testImplementation 'junit:junit:4.13.2'
    androidTestImplementation 'androidx.test.ext:junit:1.1.3'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'
    def multidex_version = "2.0.1"
    implementation "androidx.multidex:multidex:$multidex_version"
}

DBHelper.kt

package com.example.mysql_lite

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

class DBHelper(context: Context, factory: SQLiteDatabase.CursorFactory?) :
    SQLiteOpenHelper(context, DATABASE_NAME, factory, DATABASE_VERSION) {

    // below is the method for creating a database by a sqlite query
    override fun onCreate(db: SQLiteDatabase) {
        // below is a sqlite query, where column names
        // along with their data types is given
        val query = ("CREATE TABLE " + TABLE_NAME + " ("
                + ID_COL + " INTEGER PRIMARY KEY, " +
                NAME_COl + " TEXT," +
                AGE_COL + " TEXT" + ")")

        // we are calling sqlite
        // method for executing our query
        db.execSQL(query)
    }

    override fun onUpgrade(db: SQLiteDatabase, p1: Int, p2: Int) {
        // this method is to check if table already exists
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME)
        onCreate(db)
    }

    // This method is for adding data in our database
    fun addName(name : String, age : String ){

        // below we are creating
        // a content values variable
        val values = ContentValues()

        // we are inserting our values
        // in the form of key-value pair
        values.put(NAME_COl, name)
        values.put(AGE_COL, age)

        // here we are creating a
        // writable variable of
        // our database as we want to
        // insert value in our database
        val db = this.writableDatabase

        // all values are inserted into database
        db.insert(TABLE_NAME, null, values)

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

    // below method is to get
    // all data from our database
    fun getName(): Cursor? {

        // here we are creating a readable
        // variable of our database
        // as we want to read value from it
        val db = this.readableDatabase

        // below code returns a cursor to
        // read data from the database
        return db.rawQuery("SELECT * FROM " + TABLE_NAME, null)

    }

    companion object{
        // here we have defined variables for our database

        // below is variable for database name
        private val DATABASE_NAME = "GEEKS_FOR_GEEKS"

        // below is the variable for database version
        private val DATABASE_VERSION = 1

        // below is the variable for table name
        val TABLE_NAME = "gfg_table"

        // below is the variable for id column
        val ID_COL = "id"

        // below is the variable for name column
        val NAME_COl = "name"

        // below is the variable for age column
        val AGE_COL = "age"
    }
}

MainActivity.kt

package com.example.mysql_lite



import android.annotation.SuppressLint
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.Toast
import kotlinx.android.synthetic.main.activity_main.*

class MainActivity : AppCompatActivity() {

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

        // below code is to add on click
        // listener to our add name button
        addName.setOnClickListener{

            // below we have created
            // a new DBHelper class,
            // and passed context to it
            val db = DBHelper(this, null)

            // creating variables for values
            // in name and age edit texts
            val name = enterName.text.toString()
            val age = enterAge.text.toString()

            // calling method to add
            // name to our database
            db.addName(name, age)

            // Toast to message on the screen
            Toast.makeText(this, name + " added to database", Toast.LENGTH_LONG).show()

            // at last, clearing edit texts
            enterName.text.clear()
            enterAge.text.clear()
        }

        // below code is to add on click
        // listener to our print name button
        printName.setOnClickListener{

            // creating a DBHelper class
            // and passing context to it
            val db = DBHelper(this, null)

            // below is the variable for cursor
            // we have called method to get
            // all names from our database
            // and add to name text view
            val cursor = db.getName()

            // moving the cursor to first position and
            // appending value in the text view
            cursor!!.moveToFirst()

            Name.append(cursor.getString(cursor.getColumnIndex(DBHelper.NAME_COl)) + "\n")
            Age.append(cursor.getString(cursor.getColumnIndex(DBHelper.AGE_COL)) + "\n")

            // moving our cursor to next
            // position and appending values
            while(cursor.moveToNext()){
                Name.append(cursor.getString(cursor.getColumnIndex(DBHelper.NAME_COl)) + "\n")
                Age.append(cursor.getString(cursor.getColumnIndex(DBHelper.AGE_COL)) + "\n")
            }

            // at last we close our cursor
            cursor.close()
        }
    }
}