【ANDROID STUDIO】More Efficient RecyclerView Room Data Persistence Library

package com.example.roomdemo

import android.util.Patterns
import androidx.databinding.Bindable
import androidx.databinding.Observable
import androidx.lifecycle.LiveData
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>()
    private val statusMessage = MutableLiveData<Event<String>>()

    val message : LiveData<Event<String>>
    get() = statusMessage

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

    fun saveOrUpdate() {
        if (inputName.value == null) {
            statusMessage.value = Event("Please enter subscriber's name")
        } else if (inputEmail.value == null) {
            statusMessage.value = Event("Please enter subscriber's email")
        } else if (!Patterns.EMAIL_ADDRESS.matcher(inputEmail.value!!).matches()) {
            statusMessage.value = Event("Please enter a correct email address")
        } else {
            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 {
        val newRowId: Long = repository.insert(subscriber)
        if(newRowId>-1) {
            statusMessage.value = Event("Subscriber Inserted Successfully $newRowId")
        }else{
            statusMessage.value = Event("Error Occurred")
        }
    }

    fun update(subscriber: Subscriber) = viewModelScope.launch {
        val noOfRows = repository.update(subscriber)
        if(noOfRows>0) {
            inputName.value = null
            inputEmail.value = null
            isUpdateOrDelete = false
            saveOrUpdateButtonText.value = "Save"
            clearAllOrDeleteButtonText.value = "Clear All"
            statusMessage.value = Event("$noOfRows Row Updated Successfully")
        }else{
            statusMessage.value = Event("Error Occurred")
        }
    }

    fun delete(subscriber: Subscriber) = viewModelScope.launch {
        val noOfRowsDeleted = repository.delete(subscriber)
        if(noOfRowsDeleted>0){
            inputName.value = null
            inputEmail.value = null
            isUpdateOrDelete = false
            saveOrUpdateButtonText.value = "Save"
            clearAllOrDeleteButtonText.value = "Clear All"
            statusMessage.value = Event("$noOfRowsDeleted Row Deleted Successfully")
        }else{
            statusMessage.value = Event(
                "Error Occurred"
            )
        }


    }

    fun clearAll()=viewModelScope.launch {
        val noOfRowsDeleted = repository.deleteAll()
        if(noOfRowsDeleted>0) {
            statusMessage.value = Event("$noOfRowsDeleted Deleted Successfully")
        }else{
            statusMessage.value = Event("Error Occurred")
        }
    }

    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
private lateinit var adapter: MyRecyclerViewAdapter
    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()
        subscriberViewModel.message.observe(this, Observer {
            it.getContentIfNotHandled()?.let {
                Toast.makeText(this, it, Toast.LENGTH_LONG).show()
            }
        })

    }

    private fun initRecyclerView() {

        binding.subscriberRecyclerView.layoutManager = LinearLayoutManager(this)
        adapter = MyRecyclerViewAdapter({selecteditem:Subscriber->listItemClicked(selecteditem)})
        binding.subscriberRecyclerView.adapter = adapter
        displaySubscribersList()

    }

    private fun displaySubscribersList() {
        subscriberViewModel.subscribers.observe(this, Observer {
            adapter.setList(it)
            adapter.notifyDataSetChanged()

        })

    }

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

}