How to Return LiveData from Repository

Question

I just can\'t see how to chain LiveData from Repo to VM, so I have tried to boil this down to the most simple of example!:

Fragment

Answer 1

Actually If you are maintaining LiveData in repository, I don't think there's a need of separate LiveData in ViewModel as well. You just have to observe the LiveData once from the activity. Then make any changes to repository instance directly. So If I have to show it in your code, It might look something like this.

1. Activity class: Change makeToast method to observeCurrentName() like this:

   private fun observeCurrentName() {
       vm.getCurrentName().observe(this, Observer{ 
           //Toast here 
       })
   }
   

2. Your VM:

   class LoginViewModel : ViewModel() {
       ...
   
       fun getCurrentName(): MutableLiveData<String>{
           return repository.getCurrentName()
       }
   
       fun setCurrentName(name: String?){
           repository.setCurrentName(name)
       }
   
       ...
   }
   

3. Your repository:

   class FirestoreRepository {
   
       private val mCurrentName = MutableLiveData<String>()
   
       fun getCurrentName(): MutableLiveData<String>{
           return mCurrentName
       }
   
       fun setCurrentName(name: String?){
           mCurrentName.value = name //This will trigger observer in Activity
       }
   }
   

Answer 2

You're changing mCurrentName (the LiveData variable itself as opposed to it's contents) after you start observing it. The guidance seems to be to not use LiveData in Repository layer (use Coroutines/Flow instead for example)....but for now you could have something like following (or perhaps use one of the LiveData Transformations)

private val mCurrentName = firestoreRepository.currentName()

fun changeText(){
    firestoreRepository.changeText()
}

Answer 3

No need to change MutableLiveData inside ViewModel. Try to pass whatever Repository send to View. Check below

class LoginViewModel : ViewModel() {

    private val firestoreRepository : FirestoreRepository = FirestoreRepository()

    fun getCurrentName(): MutableLiveData<String> {
        return firestoreRepository.getCurrentName()
    }

    fun changeText() {
        firestoreRepository.changeText()
    }
}

And also your FirestoreRepository

class FirestoreRepository {

    private val mCurrentName = MutableLiveData<String>()

    fun getCurrentName(): MutableLiveData<String> {
        return mCurrentName
    }

    fun changeText() {
        mCurrentName.value = "Button Clicked!!"
    }
}