I have been trying to make an app that will double and triple my values into 2 textViews, and when I used viewModel, it survived all config changes. When I changed the result type to MutableLiveData the textView values don't change until I rotate the phone, after pressing my button. Here's my MainFragment

class MainFragment : Fragment() {
private var _binding: MainFragmentBinding? = null
private val binding get() = _binding!!

companion object {
    fun newInstance() = MainFragment()
}

private lateinit var viewModel: MainViewModel

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

override fun onActivityCreated(savedInstanceState: Bundle?) {
    super.onActivityCreated(savedInstanceState)
    viewModel = ViewModelProvider(this)[MainViewModel::class.java]

    binding.textView.text = viewModel.getResults().toString()
    binding.textView2.text = viewModel.getResults().toString()


    val resultsObserver = Observer<List<Float?>>{
        binding.textView.text = it[0].toString()
        binding.textView2.text = it[1].toString()
    }

    viewModel.getResults().observe(viewLifecycleOwner, resultsObserver)

    binding.action.setOnClickListener {

        if(binding.editTextNumberDecimal.text.isNotEmpty()){
            viewModel.setValues(binding.editTextNumberDecimal.text.toString())
        }else{
            binding.textView.text = getString(R.string.no)
            binding.textView2.text = getString(R.string.no1)
        }
    }
}

}

And here is my viewModel

class MainViewModel : ViewModel() {
private var input = ""

private var doubleValue = 0f

private var tripleValue = 0f

fun setValues(value: String){
    input = value
    doubleValue = input.toFloat() * 2
    tripleValue = input.toFloat() * 3
}

fun getResults(): MutableLiveData<List<Float?>> = MutableLiveData(listOf(doubleValue, tripleValue))

}

CodePudding user response：

MutableLiveData won't react automatically to the changed values you set via setValues. You will need to update the values inside of your MutableLiveData explicitly via setValue().

To achive this, I'd suggest you to store your MutableLiveData in a field of your ViewModel to be able to access it.

For example like this:

class MainViewModel : ViewModel() {

    private var input = ""

    private var doubleValue = 0f

    private var tripleValue = 0f

    private val results = MutableLiveData(listOf(doubleValue, tripleValue))

    fun setValues(value: String){
        input = value
        doubleValue = input.toFloat() * 2
        tripleValue = input.toFloat() * 3
        // This updates the value inside your LiveData
        results.value = listOf(doubleValue, tripleValue)
    }

    fun getResults(): MutableLiveData<List<Float?>> = results
}