Pass data from fragment with recyclerview to the other fragment using ViewModel in android

Question

I have a viewPager inside my application which contains 3 Fragments. First Fragment has a recyclerview on click of the item of recyclerview I pass some data to another fragment which is not the part of viewpager fragements. I am using the latest viewmodel logic to achieve this functionality and as per the steps mentioned by many websites I am doing the following this.

1. Creating the separate class which extends viewmodel

   class MovieObservable : ViewModel() {
   
   private val selectedMovieID = MutableLiveData<Int>()
   
   fun setSelectedMovieID(id : Int){
       selectedMovieID.value = id 
   }
   
   fun getSelectedMovieID(): MutableLiveData<Int> {
       return selectedMovieID
   }
   

2. Initialize the viewmodel inside oncreateView Fragment

   private lateinit var mViewModel : MovieObservable
   mViewModel = ViewModelProvider(this).get(MovieObservable::class.java)
   

3. Now from my RecyclerView I have implemented the click listener and implemented that in my fragment and override the onclick event with the position and value

   override fun onClickNowPlaying(position: Int, view: View, result: Result) {
   
   System.out.println("now playing ID" + result.id)
   mViewModel.setSelectedMovieID(result.id)
   val newFragment = MovieDetailsFragment()
   val transaction = activity?.supportFragmentManager?.beginTransaction()
   transaction?.replace(R.id.mainLayout, newFragment, "NewFragment")
   transaction?.addToBackStack(null)
   transaction?.commit()
   }
   

4. I add the logic of observing the value in the details fragment which is below

    private lateinit var mViewModel : MovieObservable
    mViewModel = ViewModelProvider(this).get(MovieObservable::class.java)
    mViewModel.getSelectedMovieID().observe(viewLifecycleOwner, Observer {getmydata->
       System.out.println("in the next fragment " + getmydata)
   })
   

So All logic is finished to pass the data from one fragment to another but the problem is I am not getting the data on the details fragment. What is it which I am missing here.

Answer 1

With latest library of ViewModel, it is even easier to create and share ViewModel between Fragments of Activity:

First add the activity-ktx and fragment-ktx dependencies in your app module's build.gradle:

dependencies {

    // For Activity
    def activity_version = "1.2.0-alpha04"
    implementation "androidx.activity:activity-ktx:$activity_version"

    // For Fragment
    def fragment_version = "1.3.0-alpha04"
    implementation "androidx.fragment:fragment-ktx:$fragment_version"

}

Suppose your ViewModel be as:

class MyViewModel : ViewModel() { }

Then, in your activity:

class MyActivity : AppCompatActivity() {

    // Use the 'by viewModels()' Kotlin property delegate 
    // from the activity-ktx artifact
    val model: MyViewModel by viewModels()
}

And then, your fragments would have:

class MyFirstFragment : Fragment() {

    // Use the 'by activityViewModels()' Kotlin property delegate
    // from the fragment-ktx artifact
    private val model: MyViewModel by activityViewModels()
}

class MySecondFragment : Fragment() {

    // Use the 'by activityViewModels()' Kotlin property delegate
    // from the fragment-ktx artifact
    private val model: MyViewModel by activityViewModels()
}