MVVM패턴에서 ViewModel의 Event 전달하기

Event.kt

open class Event<out T>(private val content: T) {

    var hasBeenHandled = false
        private set // Allow external read but not write

    /**
     * Returns the content and prevents its use again.
     */
    fun getContentIfNotHandled(): T? {
        return if (hasBeenHandled) {
            null
        } else {
            hasBeenHandled = true
            content
        }
    }

    /**
     * Returns the content, even if it's already been handled.
     */
    fun peekContent(): T = content
}

 

ViweModel

import androidx.lifecycle.LiveData
import androidx.lifecycle.MutableLiveData
import androidx.lifecycle.ViewModel
import androidx.lifecycle.viewModelScope
import com.anushka.roomdemo.db.Subscriber
import com.anushka.roomdemo.db.SubscriberRepository
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.launch
import kotlinx.coroutines.withContext

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

    val subscribers = repository.subscribers
    private var isUpdateOrDelete = false
    private lateinit var subscriberToUpdateOrDelete : Subscriber

    val inputName = MutableLiveData<String>()
    val inputEmail = MutableLiveData<String>()

    val saveOrUpdateButtonText = MutableLiveData<String>()
    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(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 = ""
            inputEmail.value = ""
        }
    }

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

    fun insert(subscriber: Subscriber) = viewModelScope.launch(Dispatchers.IO) {
           repository.insert(subscriber)
           withContext(Dispatchers.Main){
               statusMessage.value = Event("Subscriber Inserted Successfully!")
           }
       }

    fun update(subscriber: Subscriber) = viewModelScope.launch(Dispatchers.IO) {
        repository.update(subscriber)
        withContext(Dispatchers.Main){
            inputName.value = ""
            inputEmail.value = ""
            isUpdateOrDelete = false
            saveOrUpdateButtonText.value = "Save"
            clearAllOrDeleteButtonText.value = "Clear All"
            statusMessage.value = Event("Subscriber Updated Successfully!")
        }
    }

    fun delete(subscriber: Subscriber) = viewModelScope.launch(Dispatchers.IO) {
        repository.delete(subscriber)
        withContext(Dispatchers.Main){
            inputName.value = ""
            inputEmail.value = ""
            isUpdateOrDelete = false
            saveOrUpdateButtonText.value = "Save"
            clearAllOrDeleteButtonText.value = "Clear All"
            statusMessage.value = Event("Subscriber Deleted Successfully!")
        }
    }

    fun clearAll() = viewModelScope.launch(Dispatchers.IO) {
        repository.deleteAll()
        withContext(Dispatchers.Main){
            statusMessage.value = Event("All Subscribers Deleted Successfully!")
        }
    }

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



}

MainActivity

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.util.Log
import android.widget.Toast
import androidx.databinding.DataBindingUtil
import androidx.lifecycle.Observer
import androidx.lifecycle.ViewModelProvider
import androidx.recyclerview.widget.LinearLayoutManager
import com.anushka.roomdemo.databinding.ActivityMainBinding
import com.anushka.roomdemo.db.Subscriber
import com.anushka.roomdemo.db.SubscriberDatabase
import com.anushka.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)[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)
        displaySubscribersList()
    }

    private fun displaySubscribersList(){
        subscriberViewModel.subscribers.observe(this, Observer {
            Log.i("MYTAG",it.toString())
            binding.subscriberRecyclerView.adapter = MyRecyclerViewAdapter(it,{selectedItem:Subscriber->listItemClicked(selectedItem)})
        })
    }

    private fun listItemClicked(subscriber: Subscriber){
        Toast.makeText(this,"selected name is ${subscriber.name}", Toast.LENGTH_LONG).show()
        subscriberViewModel.initUpdateAndDelete(subscriber)
    }
}

 

 

참고

https://yk-coding-letter.tistory.com/5

MVVM에서 ViewModel의 Event 전달하기(Event Wrapper)

https://medium.com/androiddevelopers/livedata-with-snackbar-navigation-and-other-events-the-singleliveevent-case-ac2622673150

LiveData with SnackBar, Navigation and other events (the SingleLiveEvent case)