LiveData learning

new_user_entry.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <EditText
        android:id="@+id/txtName"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="32dp"
        android:layout_marginTop="32dp"
        android:layout_marginEnd="32dp"
        android:ems="10"
        android:inputType="text"
        android:hint="Name"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <EditText
        android:id="@+id/txtMobNo"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="32dp"
        android:layout_marginTop="24dp"
        android:layout_marginEnd="32dp"
        android:ems="10"
        android:inputType="text"
        android:hint="Mob No"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/txtName" />

    <Button
        android:id="@+id/btnSubmit"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="32dp"
        android:layout_marginTop="24dp"
        android:layout_marginEnd="32dp"
        android:text="Submit"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/txtMobNo" />

    <View
        android:id="@+id/divider"
        android:layout_width="0dp"
        android:layout_height="2dp"
        android:layout_marginStart="1dp"
        android:layout_marginTop="32dp"
        android:layout_marginEnd="1dp"
        android:background="?android:attr/listDivider"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/btnSubmit" />

    <TextView
        android:id="@+id/txtDisplayName"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="32dp"
        android:layout_marginTop="32dp"
        android:layout_marginEnd="32dp"
        android:text="name"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/divider" />

    <TextView
        android:id="@+id/txtDisplayMob"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="32dp"
        android:layout_marginTop="32dp"
        android:layout_marginEnd="32dp"
        android:text="mob no"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/txtDisplayName" />

    <View
        android:id="@+id/divider2"
        android:layout_width="409dp"
        android:layout_height="1dp"
        android:layout_marginStart="1dp"
        android:layout_marginTop="58dp"
        android:layout_marginEnd="1dp"
        android:background="?android:attr/listDivider"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/txtTransformText" />

    <TextView
        android:id="@+id/txtCount"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="32dp"
        android:layout_marginTop="24dp"
        android:layout_marginEnd="32dp"
        android:text="Count"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/txtDisplayMob" />

    <TextView
        android:id="@+id/txtTransformText"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="32dp"
        android:layout_marginTop="16dp"
        android:layout_marginEnd="32dp"
        android:text="transform text"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/txtCount" />
</androidx.constraintlayout.widget.ConstraintLayout>

NewUserEntryFragment.kt

package com.example.coroutinelearning.fragments

import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.fragment.app.Fragment
import androidx.fragment.app.activityViewModels
import androidx.lifecycle.Observer
import com.example.coroutinelearning.databinding.NewUserEntryBinding
import com.example.coroutinelearning.entity.User
import com.example.coroutinelearning.viewModels.UserViewModel

class NewUserEntryFragment : Fragment() {

    private val TAG = NewUserEntryFragment::class.simpleName
    private lateinit var binding: NewUserEntryBinding
    private val userViewModel: UserViewModel by activityViewModels()

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

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

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        binding.btnSubmit.setOnClickListener {
            saveUserDetailToDB()
            observeNewUser()
            observeNameCount()
            observerTransformationMap()
        }
    }

    private fun observerTransformationMap() {
        userViewModel.transformLiveDataExample.observe(viewLifecycleOwner) {
            binding.txtTransformText.text = it
        }
    }

    private fun observeNameCount() {
        // userViewModel.wordCount.value = 10 -> error-> because in viewmodel we created livedata in such way that fragment will
        //only be able to observe, but not change it in observer.
        userViewModel.wordCount.observe(viewLifecycleOwner) { count ->
            binding.txtCount.text = count.toString()
        }
    }

    private fun observeNewUser() {
//        val user = User(name = "sohan", mobileNumber = "3729857329")
//        userViewModel.newUserData.value = user
        userViewModel.newUserData.observe(viewLifecycleOwner, Observer { user ->
            binding.txtDisplayName.text = user.name
            binding.txtDisplayMob.text = user.mobileNumber
        })
    }

    private fun saveUserDetailToDB() {
        val name = binding.txtName.text.toString()
        val mobNo = binding.txtMobNo.text.toString()
        val user = User(name = name, mobileNumber = mobNo)
        userViewModel.saveUserDetail(user)
    }
}

UserViewModel.kt

package com.example.coroutinelearning.viewModels

import android.app.Application
import android.view.animation.Transformation
import androidx.lifecycle.AndroidViewModel
import androidx.lifecycle.LiveData
import androidx.lifecycle.MutableLiveData
import androidx.lifecycle.map
import androidx.lifecycle.viewModelScope
import com.example.coroutinelearning.entity.User
import com.example.coroutinelearning.repositories.UserRepository
import kotlinx.coroutines.launch

class UserViewModel(application: Application) : AndroidViewModel(application) {

    private val userRepository: UserRepository

    val userListLiveData: MutableLiveData<List<User>> = MutableLiveData<List<User>>()
    val newUserData: MutableLiveData<User> = MutableLiveData()
    var transformLiveDataExample: LiveData<String> = MutableLiveData()

    private val _wordCount = MutableLiveData<Int>()
    val wordCount: LiveData<Int> //in this way you are restriction other acitivity/fragment from set method -> which is good.
        get() = _wordCount


    init {
        userRepository = UserRepository(application)
    }

    fun saveUserDetail(user: User) {
        viewModelScope.launch {
            userRepository.saveUserDetail(user)
            newUserData.value = user
            _wordCount.value = user.name.length
            //transform liveData feature-> if you like to do some manipulation in livedata
            transformLiveDataExample = newUserData.map { user ->
                user.name + user.mobileNumber
            }
        }
    }

    fun viewUserDetail(): LiveData<List<User>> {
        viewModelScope.launch {
            val userList = userRepository.viewUserDetail()
            userListLiveData.value = userList
        }
        return userListLiveData
    }

}