I don't quite understand the behavior of MutableLiveData or I can't find the proper documentation.

But I need help.

1. I need to add an element to the first position of the array and tried with "plus" but it doesn't work properly. Or is there a way to add multiple elements of an array in the first position?

_series.value = _series.value?.plus(it) // ??? 11111111

2. I can't figure out how to delete all the elements of the array, I did it with

_series.value = null // ??? 2222222

_series.value = ArrayList() /// ??? 2222222

but I don't think it is the best way to do it.

class SerieViewModel(val database: SerieDatabaseDao) : ViewModel() {
    private val _series = MutableLiveData<List<Serie>?>()
    val series: LiveData<List<Serie>?>
        get() = _series

    fun fetchSeries(code: String) { 
        viewModelScope.launch {
            try {
                val response = CodesApi.retrofitService.getSeries(code)
                val series = response.body()?.data          
                series?.forEach {
                  _series.value = _series.value?.plus(it) // ??? 11111111
                  }
                }

            } catch (e: Exception) {
                Log.d(TAG, "fetchSeries: ${e.message}")
            }    
        }
    }

    fun clearDb() = viewModelScope.launch {
        database.clear() 
        _series.value = null  // ??? 2222222
        _series.value = ArrayList<Serie>()  /// ??? 2222222
    }

thanks

CodePudding user response：

1. You are storing a List<Serie?> which is fine thats what you should do, but you can't add elements to List, you need to convert List to ArrayList and add elements to the ArrayList than update the MutableLiveData, follow the code below.

2. to clear all the elements from the List you can set the value to emptyList(), follow the code below.

Note: Take a look about the difference between List, ArrayList, Array in kotlin they are not the same

class SerieViewModel(val database: SerieDatabaseDao) : ViewModel() {
    private val _series = MutableLiveData<List<Serie>?>()
    val series: LiveData<List<Serie>?>
        get() = _series

    fun fetchSeries(code: String) {
        viewModelScope.launch {
            try {
                val response = CodesApi.retrofitService.getSeries(code)
                val series = response.body()?.data
                val liveDataSeries =
                    if (_series.value == null) emptyList<Serie>() // set the array list to empty if _series.value is null
                    else ArrayList(_series.value) // else: add _series.value elements to the array list
                series?.forEach {
                    liveDataSeries.add(it) // add each serie to the array list
                }
                _series.value = liveDataSeries // update _series.value
            } catch (e: Exception) {
                Log.d(TAG, "fetchSeries: ${e.message}")
            }
        }
    }

    fun clearDb() = viewModelScope.launch {
        database.clear()
        _series.value = emptyList()
    }

}