Understanding Persistence Data Storage in Android

build.gradle

//Module-app (gradle)
dependencies {

// Room
    implementation "androidx.room:room-runtime:2.4.3"
    kapt "androidx.room:room-compiler:2.4.3"

    // Kotlin Extensions and Coroutines support for Room
    implementation "androidx.room:room-ktx:2.4.3"

    // Coroutines
    implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-core:1.6.1'
    implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.6.1'
}

Constants.kt

const val TOKEN = "TOKEN"

const val DESIGNER = "DESIGNER"

Dao.kt

@Dao
interface Dao {

//Inserting data

    @Insert
    suspend fun insertNFTs(nft: NFTs)

//Fetching data using simple SQL Query

    @Transaction
    @Query("SELECT * FROM NFTs")
    suspend fun getMyNFTs() : List<NFTs>
}

database.kt

@Database(
    entities = [
        NFTs::class,
               ], version = 1)

abstract class database : RoomDatabase() {

    abstract val dao: Dao

    companion object {

        @Volatile
        private var instance: database? = null

        fun getInstance(context: Context): database {

            synchronized(this) {

                return instance ?: Room.databaseBuilder(
                    context.applicationContext,
                    database::class.java,
                    "my_nft_collection" //DATABASE_NAME
                ).fallbackToDestructiveMigration()
                    .build().also {
                    instance = it
                }
            }
        }
    }
}

MainAcctivity.kt

class MainAcctivity : AppCompatActivity() {

    private lateinit var binding: AcctivityMainBinding

    private val prefRepository by lazy { PrefRepository(this) }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        binding = AcctivityMainBinding.inflate(layoutInflater)
        
         prefRepository.setToken("buyme123")
         prefRepository.setDesigner("sick?yes")
       
        setContentView(binding.root)
    }
}

MainActivity.kt

    private lateinit var data: Dao

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        data = database.getInstance(this).dao
        
        CoroutineScope(Dispatchers.IO).async {
        
        data.insertNFTs("123Buyme","Sick?yes","Most Popular")
        data.getMyNFTs()
        }
   }

NFTs.kt

@Entity
data class NFTs(
    @PrimaryKey(autoGenerate = false)
    var token: String,
    var designer : String? = null,
    var desc : String? = null
    )

PrefRepository.kt

class PrefRepository(val context: Context) {

    private val pref: SharedPreferences = context.getSharedPreferences(PREFERENCE_NAME, Context.MODE_PRIVATE)

    private val editor = pref.edit()

    private val gson = Gson()

    private fun String.put(long: Long) {
        editor.putLong(this, long)
        editor.commit()
    }

    private fun String.put(int: Int) {
        editor.putInt(this, int)
        editor.commit()
    }

    private fun String.put(string: String) {
        editor.putString(this, string)
        editor.commit()
    }

    private fun String.put(boolean: Boolean) {
        editor.putBoolean(this, boolean)
        editor.commit()
    }
    //clear
    private fun String.clear() {
        editor.remove(this)
        editor.commit()
    }

    private fun String.getLong() = pref.getLong(this, 0)

    private fun String.getInt() = pref.getInt(this, 0)

    private fun String.getString() = pref.getString(this, "")!!

    private fun String.getBoolean() = pref.getBoolean(this, false)


    fun setToken(token : String){
        TOKEN.put(token)
    }

    fun getToken() = TOKEN.getString()

    fun setDesigner(designer : String){
        DESIGNER.put(designer)
    }

    fun getDesigner() = DESIGNER.getString()

    fun clearData() {
        editor.clear()
        editor.commit()
    }

}