I am encountering an issue with my Kotlin Android code while implementing a Spinner with an onItemSelectedListener. I am trying to populate the Spinner with data retrieved from a SQLite database, but I keep encountering a NullPointerException when trying to access the Spinner within the onItemSelected method.
Here's a snippet of my code:
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
) {
// NullPointerException occurs here
selectedItem = parent?.getItemAtPosition(position).toString()
Toast.makeText(this@SecondActivity, selectedItem, Toast.LENGTH_SHORT).show()
}
}
I think there must be some issue with the CRUD operations , I woulld love if anyone could give me a rundown
This is everything you need to do to set up CRUD operations in Kotlin using SQLite. In your code you havent added the condition of not having anything selected , thats why you are facing this issue
DATABASE
Go to AndroidManifest.xml
add these permissions -
<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>
Make New Class DatabaseHelper and add the code below -
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()
}
}
FINDING SPECIFIC INPUT
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)
}
SELECTING COUNT OF ROLLNUMBERS OF SIMILAR NAMES
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)
}
SELECTING NAMES AND MARKS OF THE STUDENT WITH THE HIGHEST MARKS & STUDENT WITH THE LOWEST MARKS
DatabaseHelper
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())
}
DATABASE DISPLAY IN 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
}
ADDING DATABASE TO SPINNER
var spinner = findViewById<Spinner>(R.id.spinner)
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")
}
}
check this link for other views - Kotlin code reports "None of the following functions can be called with the arguments supplied"