Values are not added in MutableLiveData<MutableList<String>>()

Question

I am using a fragment and viewmodel where the list values are not updated in the viemodel when the function is called from my fragment.

This is in my fragment

class SettingsFragment : Fragment() {

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
    val binding = FragmentSettingsBinding.inflate(inflater)
    val application = requireNotNull(this.activity).application
    val dataSource = UserInfoDatabase.getInstance(application).userInfoDao
    val viewModelFactory = SettingsViewModelFactory(dataSource, application)
    val settingsViewModel = ViewModelProvider(this, viewModelFactory).get(SettingsViewModel::class.java)
    binding.settingsViewModel = settingsViewModel
    binding.lifecycleOwner = this
    settingsViewModel.addValueToList("hello")
  }
}

This is from my ViewModel

class SettingsViewModel(val database: UserInfoDatabaseDao, application: Application): AndroidViewModel(application){
    private val _sectionList = MutableLiveData<MutableList<String>>()
    val sectionList: MutableLiveData<MutableList<String>>
        get() = _sectionList
    fun addValueToList(listValue: String){
    _sectionList.value?.add(listValue)
    }
 } 

When I try to print a toast message as _sectionList.value.toString() from my viewModel after trying to add values to the list, it shows null.

Thanks in advance for the help..

Answer 1

It's because you have not initialized the MutableList<>().

class SettingsViewModel(val database: UserInfoDatabaseDao, application: Application): AndroidViewModel(application){

    private val _sectionList = MutableLiveData<MutableList<String>>()

    val sectionList: MutableLiveData<MutableList<String>>
        get() = _sectionList

    fun addValueToList(listValue: String){

       // In the following line: _sectionList.value is still null, so this will 
       // never call the add
        _sectionList.value?.add(listValue)
    }
 } 

If you initialize with:

init {
    _sectionList.value = mutableListOf<String>()
}

it should work hopefully.