I'm relative new to Android programming and read a few things about ViewModel, Fragments. What i'm trying is to create an app with a few fragments. It needs to be able to send data from the MainActivity to different fragments and from the Fragments back to the Main activity.
I am able to send data from the main activity to the Fragment page but I am not able to use the ModelView and use that in combination with an observer.
For this example I used the basic project in Android Studio with the Navigation Drawer Views Activity.
MainActivity:
package com.example.eriksslider
import android.os.Bundle
import android.view.Menu
import androidx.activity.viewModels
import com.google.android.material.snackbar.Snackbar
import com.google.android.material.navigation.NavigationView
import androidx.navigation.findNavController
import androidx.navigation.ui.AppBarConfiguration
import androidx.navigation.ui.navigateUp
import androidx.navigation.ui.setupActionBarWithNavController
import androidx.navigation.ui.setupWithNavController
import androidx.drawerlayout.widget.DrawerLayout
import androidx.appcompat.app.AppCompatActivity
import androidx.fragment.app.viewModels
import com.example.eriksslider.databinding.ActivityMainBinding
import com.example.eriksslider.ui.home.HomeFragment
import com.example.eriksslider.ui.home.HomeViewModel
class MainActivity : AppCompatActivity() {
private lateinit var appBarConfiguration: AppBarConfiguration
private lateinit var binding: ActivityMainBinding
private val viewModel: HomeViewModel by viewModels()
val homeFragment = HomeFragment()
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = ActivityMainBinding.inflate(layoutInflater)
setContentView(binding.root)
setSupportActionBar(binding.appBarMain.toolbar)
binding.appBarMain.fab.setOnClickListener { view ->
viewModel.setText("Hallo")
homeFragment.test("Hallo")
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show()
}
val drawerLayout: DrawerLayout = binding.drawerLayout
val navView: NavigationView = binding.navView
val navController = findNavController(R.id.nav_host_fragment_content_main)
// Passing each menu ID as a set of Ids because each
// menu should be considered as top level destinations.
appBarConfiguration = AppBarConfiguration(
setOf(
R.id.nav_home, R.id.nav_gallery, R.id.nav_slideshow
), drawerLayout
)
setupActionBarWithNavController(navController, appBarConfiguration)
navView.setupWithNavController(navController)
}
override fun onCreateOptionsMenu(menu: Menu): Boolean {
// Inflate the menu; this adds items to the action bar if it is present.
menuInflater.inflate(R.menu.main, menu)
return true
}
override fun onSupportNavigateUp(): Boolean {
val navController = findNavController(R.id.nav_host_fragment_content_main)
return navController.navigateUp(appBarConfiguration) || super.onSupportNavigateUp()
}
}
Home Fragment:
package com.example.eriksslider.ui.home
import android.os.Bundle
import android.util.Log
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.TextView
import androidx.fragment.app.Fragment
import androidx.fragment.app.viewModels
import androidx.lifecycle.ViewModelProvider
import com.example.eriksslider.databinding.FragmentHomeBinding
class HomeFragment : Fragment() {
private var _binding: FragmentHomeBinding? = 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 {
val homeViewModel =
ViewModelProvider(this)[HomeViewModel::class.java]
_binding = FragmentHomeBinding.inflate(inflater, container, false)
val root: View = binding.root
val textView: TextView = binding.textView2
homeViewModel.text.observe(viewLifecycleOwner) {
textView.text = it
}
return root
}
override fun onDestroyView() {
super.onDestroyView()
_binding = null
}
fun test(value: String){
Log.d("Home Fragment", value)
}
}
And the modelview:
package com.example.eriksslider.ui.home
import androidx.lifecycle.LiveData
import androidx.lifecycle.MutableLiveData
import androidx.lifecycle.ViewModel
class HomeViewModel : ViewModel() {
private val _text = MutableLiveData<String>()
val text: LiveData<String> = _text
fun setText(value: String){
_text.value = value
}
}
fragment_home file
<?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"
tools:context=".ui.home.HomeFragment">
<TextView
android:id="@+id/text_home"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="8dp"
android:textAlignment="center"
android:textSize="20sp"
android:text="TextView"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<TextView
android:id="@+id/textView2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="TextView"
app:layout_constraintTop_toBottomOf="@+id/text_home"
tools:layout_editor_absoluteX="175dp" />
</androidx.constraintlayout.widget.ConstraintLayout>
If i look at the Logcat i can see when i press the button that the data is sent to the HomeFragment and that's basiclyit. The TextView is not updated at all. My question is this post is, how can I get the data sent from MainActivity displayed on the Home Fragment page?
It seems the fragment is creating a new HomeViewModel. To get a view model from an activity, use activityViewModels delegation.
MainActivity
class MainActivity : AppCompatActivity() {
private lateinit var appBarConfiguration: AppBarConfiguration
private lateinit var binding: ActivityMainBinding
private val viewModel: HomeViewModel by viewModels()
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = ActivityMainBinding.inflate(layoutInflater)
setContentView(binding.root)
setSupportActionBar(binding.appBarMain.toolbar)
binding.appBarMain.fab.setOnClickListener { view ->
viewModel.setText("Hallo")
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show()
}
val drawerLayout: DrawerLayout = binding.drawerLayout
val navView: NavigationView = binding.navView
val navController = findNavController(R.id.nav_host_fragment_content_main)
// Passing each menu ID as a set of Ids because each
// menu should be considered as top level destinations.
appBarConfiguration = AppBarConfiguration(
setOf(
R.id.nav_home, R.id.nav_gallery, R.id.nav_slideshow
), drawerLayout
)
setupActionBarWithNavController(navController, appBarConfiguration)
navView.setupWithNavController(navController)
}
override fun onCreateOptionsMenu(menu: Menu): Boolean {
// Inflate the menu; this adds items to the action bar if it is present.
menuInflater.inflate(R.menu.main, menu)
return true
}
override fun onSupportNavigateUp(): Boolean {
val navController = findNavController(R.id.nav_host_fragment_content_main)
return navController.navigateUp(appBarConfiguration) || super.onSupportNavigateUp()
}
}
HomeFragment
class HomeFragment : Fragment() {
private var _binding: FragmentHomeBinding? = null
private val binding get() = _binding!!
private val homeViewModel by activityViewModels<HomeViewModel>()
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View {
_binding = FragmentHomeBinding.inflate(inflater, container, false)
val root: View = binding.root
val textView: TextView = binding.textView2
homeViewModel.text.observe(viewLifecycleOwner) {
textView.text = it
}
return root
}
override fun onDestroyView() {
super.onDestroyView()
_binding = null
}
}