Kotlin: How to change values of MutableLiveData in ViewModel without using getters and setters

Question

Here is my viewmodel:

class MyProfileEditSharedViewModel : ViewModel() {
    val question = MutableLiveData<String>()
    val answer = MutableLiveData<String>()

    fun setQuestion (q: String) {
        question.value = q
    }

    fun setAnswer (a: String) {
        answer.value = a
    }
}

I set the data using setQuestion and setAnswer like this:

viewModel.setQuestion(currentUserInList.question)
viewModel.setAnswer(currentUserInList.answer)

I try to get question and answer from the ViewModel like this:

val qnaQuestionData = communicationViewModel.question as String
val qnaAnswerData = communicationViewModel.answer as String

Compiler says I cannot cast MutableLiveData to string. Should I make a separate getter like my setter? I heard that you don't need to use getters and setters in kotlin, is there anyway to edit val question and val answer in my viewmodel without using getters and setters?

Thank you!!

You should be observing LiveData to get notified of changes in it, and not pulling data manually. See the docs: developer.android.com/topic/libraries/architecture/… — zsmb13
You would use something like val qnaQuestionData = communicationViewModel.question.value ?: someDefault, but typically you don't want to be retrieving a LiveData's value synchronously because it defeats the purpose of using LiveData. — Tenfour04

Edward Edward · Accepted Answer · 2020-06-22T13:59:10

Create some sort of getter method in your ViewModel

fun getQuestion(): LiveData<String> {
        return question //this works because MutableLiveData is a subclass of LiveData
}

Then, you can observe the value in whatever class you care about the value. ie:

communicationsViewModel.getQuestion().observe(this, Observer {
       //do something with the value which is 'it'. Maybe qnaQuestionData = it
}

Note if you're trying to observe the value from a fragment or something, you will have to change the parameter this, to viewLifecycleOwner

Kotlin: How to change values of MutableLiveData in ViewModel without using getters and setters

2 Answers