【ANDROID STUDIO】CRUD Room Data Persistence Library

 package com.example.roomdemo

import androidx.databinding.Bindable
import androidx.databinding.Observable
import androidx.lifecycle.MutableLiveData
import androidx.lifecycle.ViewModel
import androidx.lifecycle.viewModelScope
import com.example.roomdemo.db.Subscriber
import com.example.roomdemo.db.SubscriberRepository
import kotlinx.coroutines.launch

class SubscriberViewModel(private val repository: SubscriberRepository) : ViewModel(),Observable {

    val subscribers = repository.subscribers
    private var isUpdateOrDelete = false
    private lateinit var subscriberToUpdateOrDelete : Subscriber
    @Bindable
    val inputName = MutableLiveData<String>()
    @Bindable
    val inputEmail = MutableLiveData<String>()
    @Bindable
    val saveOrUpdateButtonText = MutableLiveData<String>()
    @Bindable
    val clearAllOrDeleteButtonText = MutableLiveData<String>()

    init {
        saveOrUpdateButtonText.value = "Save"
        clearAllOrDeleteButtonText.value = "Clear All"
    }

    fun saveOrUpdate() {
        if(isUpdateOrDelete) {
            subscriberToUpdateOrDelete.name = inputName.value!!
            subscriberToUpdateOrDelete.email = inputEmail.value!!
            update(subscriberToUpdateOrDelete)
        }else {

            val name = inputName.value!!
            val email = inputEmail.value!!
            insert(Subscriber(0, name, email))
            inputName.value = null
            inputEmail.value = null
        }
    }

    fun clearAllOrDelete() {
        if(isUpdateOrDelete) {
            delete(subscriberToUpdateOrDelete)
        }else {
            clearAll()
        }
    }

    fun insert(subscriber: Subscriber)= viewModelScope.launch {
        repository.insert(subscriber)
    }

    fun update(subscriber: Subscriber) = viewModelScope.launch {
        repository.update(subscriber)
        inputName.value = null
        inputEmail.value = null
        isUpdateOrDelete = false
        saveOrUpdateButtonText.value = "Save"
        clearAllOrDeleteButtonText.value = "Clear All"
    }

    fun delete(subscriber: Subscriber) = viewModelScope.launch {
        repository.delete(subscriber)
        inputName.value = null
        inputEmail.value = null
        isUpdateOrDelete = false
        saveOrUpdateButtonText.value = "Save"
        clearAllOrDeleteButtonText.value = "Clear All"

    }

    fun clearAll()=viewModelScope.launch {
        repository.deleteAll()
    }

    fun initUpdateAndDelete(subscriber: Subscriber) {
        inputName.value = subscriber.name
        inputEmail.value = subscriber.email
        isUpdateOrDelete = true
        subscriberToUpdateOrDelete = subscriber
        saveOrUpdateButtonText.value = "Update"
        clearAllOrDeleteButtonText.value = "Delete"

    }


    override fun removeOnPropertyChangedCallback(callback: Observable.OnPropertyChangedCallback?) {

    }

    override fun addOnPropertyChangedCallback(callback: Observable.OnPropertyChangedCallback?) {

    }
}

package com.example.roomdemo

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.Toast
import androidx.databinding.DataBindingUtil
import androidx.lifecycle.Observer
import androidx.lifecycle.ViewModelProvider
import androidx.recyclerview.widget.LinearLayoutManager
import com.example.roomdemo.databinding.ActivityMainBinding
import com.example.roomdemo.db.Subscriber
import com.example.roomdemo.db.SubscriberDatabase
import com.example.roomdemo.db.SubscriberRepository

class MainActivity : AppCompatActivity() {
    private lateinit var binding: ActivityMainBinding
    private lateinit var subscriberViewModel: SubscriberViewModel

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = DataBindingUtil.setContentView(this,R.layout.activity_main)
        val dao = SubscriberDatabase.getInstance(application).subscriberDAO
        val repository = SubscriberRepository(dao)
        val factory = SubscriberViewModelFactory(repository)
        subscriberViewModel = ViewModelProvider(this,factory).get(SubscriberViewModel::class.java)
        binding.myViewModel = subscriberViewModel
        binding.lifecycleOwner = this
         initRecyclerView()

    }

    private fun initRecyclerView() {

        binding.subscriberRecyclerView.layoutManager = LinearLayoutManager(this)
        displaySubscribersList()

    }

    private fun displaySubscribersList() {
        subscriberViewModel.subscribers.observe(this, Observer {
            binding.subscriberRecyclerView.adapter = MyRecyclerViewAdapter(it, {selecteditem:Subscriber->listItemClicked(selecteditem)})
        })

    }

    private fun listItemClicked(subscriber: Subscriber) {
        subscriberViewModel.initUpdateAndDelete(subscriber)
    }

}

package com.example.roomdemo

import android.view.LayoutInflater
import android.view.ViewGroup
import androidx.databinding.DataBindingUtil
import androidx.recyclerview.widget.RecyclerView
import com.example.roomdemo.databinding.ListItemBinding
import com.example.roomdemo.db.Subscriber

class MyRecyclerViewAdapter(
    private val subscribersList: List<Subscriber>,
    private val clickListener: (Subscriber) -> Unit
) : RecyclerView.Adapter<MyViewHolder>() {
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyViewHolder {
        val layoutInflater = LayoutInflater.from(parent.context)
        val binding: ListItemBinding =
            DataBindingUtil.inflate(layoutInflater, R.layout.list_item, parent, false)
        return MyViewHolder(binding)
    }

    override fun getItemCount(): Int {
        return subscribersList.size
    }

    override fun onBindViewHolder(holder: MyViewHolder, position: Int) {
        holder.bind(subscribersList[position], clickListener)
    }

}

class MyViewHolder(val binding: ListItemBinding) : RecyclerView.ViewHolder(binding.root) {

    fun bind(subscriber: Subscriber, clickListener: (Subscriber) -> Unit) {
        binding.nameTextView.text = subscriber.name
        binding.emailTextView.text = subscriber.email
        binding.listItemLayout.setOnClickListener{
            clickListener(subscriber)
        }
    }
}
package com.example.roomdemo

import androidx.lifecycle.ViewModel
import androidx.lifecycle.ViewModelProvider
import com.example.roomdemo.db.SubscriberRepository

class SubscriberViewModelFactory(private val repository: SubscriberRepository) : ViewModelProvider.Factory {
    override fun <T : ViewModel?> create(modelClass: Class<T>): T {
        if (modelClass.isAssignableFrom(SubscriberViewModel::class.java)) {
            return SubscriberViewModel(repository) as T
        }
        throw IllegalArgumentException("Unknown View Model class")
    }
}

package com.example.roomdemo.db

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

@Entity(tableName = "subscriber_data_table")
data class Subscriber (

    @PrimaryKey(autoGenerate = true)
    @ColumnInfo(name = "subscriber_name")
    var id : Int,

    @ColumnInfo(name = "subscriber_id")
    var name : String,

    @ColumnInfo(name = "subscriber_email")
    var email : String
)

package com.example.roomdemo.db

import androidx.lifecycle.LiveData
import androidx.room.*

@Dao
interface SubscriberDAO {
    @Insert
    suspend fun insertSubscriber(subscriber: Subscriber): Long

    @Update
    suspend fun updateSubscriber(subscriber: Subscriber)

    @Delete
    suspend fun deleteSubscriber(subscriber: Subscriber)

    @Query("DELETE FROM subscriber_data_table")
    suspend fun deleteAll()

    @Query("SELECT * FROM subscriber_data_table")
    fun getAllSubscribers(): LiveData<List<Subscriber>>
}

package com.example.roomdemo.db

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

@Database(entities = [Subscriber::class],version = 1)
abstract class SubscriberDatabase : RoomDatabase() {

    abstract val subscriberDAO: SubscriberDAO

    companion object {
        @Volatile
        private var INSTANCE: SubscriberDatabase? = null
        fun getInstance(context: Context): SubscriberDatabase {
            synchronized(this) {
                var instance = INSTANCE
                if (instance == null) {
                    instance = Room.databaseBuilder(
                        context.applicationContext,
                        SubscriberDatabase::class.java,
                        "subscriber_data_database"
                    ).build()
                }
                return instance
            }
        }

    }
}

package com.example.roomdemo.db

class SubscriberRepository(private val dao : SubscriberDAO) {

    val subscribers = dao.getAllSubscribers()

    suspend fun insert(subscriber: Subscriber) {
        dao.insertSubscriber(subscriber)
    }

    suspend fun update(subscriber: Subscriber) {
        dao.updateSubscriber(subscriber)
    }

    suspend fun delete(subscriber: Subscriber) {
        dao.deleteSubscriber(subscriber)
    }

    suspend fun deleteAll() {
        dao.deleteAll()
    }
}