How to populate a Spinner with Room database in Kotlin

In this android kotlin source code example, we are going to populate a Spinner with Room database in Kotlin.

You can copy and adopt this source code example to your Kotlin android project without reinventing the wheel.

Below is a step by step source code to populate a Spinner with Room database in Kotlin.

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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:padding="24dp"
    tools:context=".spinner.SpinnerActivity14">

    <Spinner
        android:id="@+id/spinner"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"/>

</androidx.constraintlayout.widget.ConstraintLayout>

MainActivity.kt

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.ArrayAdapter
import android.widget.Spinner
import com.bluapp.kotlinview.R

class SpinnerActivity14 : AppCompatActivity() {
    private var spinnerDatabase: SpinnerDatabase? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_spinner14)
        val spinner = findViewById(R.id.spinner) as Spinner
        spinnerDatabase = SpinnerDatabase.getInstance(this)
        val usernameSpinner = Spinner14(id = null, username = "Clark")
        spinnerDatabase!!.spinnerDAO().insert(usernameSpinner)
        val username = spinnerDatabase!!.spinnerDAO().allSpinner()
        val item = arrayOfNulls<String>(username.size)
        for(i in 0 until username.size){
            item[i] = username.get(i).username
        }
        val arrayadapter = ArrayAdapter(this@SpinnerActivity14, android.R.layout.simple_spinner_item, item)
        spinner.adapter = arrayadapter
    }
}

SpinnerDatabase.java

import android.content.Context
import androidx.room.Database
import androidx.room.Room
import androidx.room.RoomDatabase

@Database(entities = arrayOf(Spinner14::class), version = 1, exportSchema = false)
abstract class SpinnerDatabase : RoomDatabase() {
    abstract fun spinnerDAO(): SpinnerDAO

    companion object {
        private var instance: SpinnerDatabase? = null

        fun getInstance(context: Context): SpinnerDatabase {
            if (instance == null) {
                instance =
                    Room.databaseBuilder(context, SpinnerDatabase::class.java, "spinnerdb")
                        .fallbackToDestructiveMigration()
                        .allowMainThreadQueries()
                        .build()
            }
            return instance as SpinnerDatabase
        }

        fun destroyInstance() {
            instance = null
        }
    }
}

SpinnerDAO.java

import androidx.room.Dao
import androidx.room.Insert
import androidx.room.OnConflictStrategy.REPLACE
import androidx.room.Query

@Dao
interface SpinnerDAO {

    @Query("select * from spinner")
    fun allSpinner(): List<Spinner14>

    @Insert(onConflict = REPLACE)
    fun insert(spinner14: Spinner14)
}

Spinner14.java

import androidx.room.ColumnInfo
import androidx.room.Entity
import androidx.room.PrimaryKey

@Entity(tableName = "spinner")
data class Spinner14(
    @PrimaryKey
    var id: Long?,
    @ColumnInfo(name = "username")
    var username: String
)

app/build.gradle

implementation 'androidx.room:room-runtime:2.2.1'
kapt 'androidx.room:room-compiler:2.2.1'

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