android mvvm livedata postvalue example

postvalue.kt

package com.example.myapplication

import android.os.Bundle
import androidx.fragment.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.fragment.app.viewModels
import androidx.lifecycle.LiveData
import androidx.lifecycle.MutableLiveData
import androidx.lifecycle.Observer
import androidx.lifecycle.ViewModel
import androidx.navigation.fragment.findNavController
import com.example.myapplication.databinding.FragmentFirstBinding

/**
 * A simple [Fragment] subclass as the default destination in the navigation.
 */
class FirstFragment : Fragment() {

    private val viewModel: MyViewModel by viewModels()

    private var _binding: FragmentFirstBinding? = null

    // This property is only valid between onCreateView and
    // onDestroyView.
    private val binding get() = _binding!!

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View {
        _binding = FragmentFirstBinding.inflate(inflater, container, false)
        return binding.root
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        viewModel.monInformation.observe(viewLifecycleOwner, Observer {
            _binding?.textviewFirst?.text = it
        })

        viewModel.getInformation()

        binding.buttonFirst.setOnClickListener {
            findNavController().navigate(R.id.action_FirstFragment_to_SecondFragment)
        }
    }

    override fun onDestroyView() {
        super.onDestroyView()
        _binding = null
    }
}


class MyViewModel : ViewModel() {
    //val monInformation: MutableLiveData<String> get() = getInformation()
    val monInformation = MutableLiveData<String>()

//    private fun getInformation(): MutableLiveData<String> {
//        return MyRepository().getInformation()
//        //monInformation.postValue("hello")
//    }

    fun getInformation() {
        monInformation.postValue("hello")
    }

    override fun onCleared() {
        super.onCleared()
        // cleanup ici
    }
}


class MyRepository {
    fun getInformation(): MutableLiveData<String> {
        return MutableLiveData("hello")
    }
}