How to use the information stored in mutableStateOf in Jetpack Compose - kotlin

Question

I have information in json and I retrieve it using retrofit2, everything works fine, I get the data in a List.
I need this information to fill elements in Jetpack Compose for which I use mutableStateOf to save the states.
My function that I use is the following:
fun jsonParsing(
dataRecox: MutableState<List<Event>>
) {
val TAG_LOGS = "Mariox"
val retrofit = Retrofit.Builder()
.baseUrl("http://myserversample.com/pGet/track/")
.addConverterFactory(GsonConverterFactory.create())
.build()
val retrofitAPI = retrofit.create(APIService1::class.java)
retrofitAPI.getRecolector().enqueue(object : Callback<List<Event>> {
override fun onResponse(
call: Call<List<Event>>,
response: Response<List<Event>>
) {
val data = response.body()
val mydata = data!!
dataRecox.value = mydata
Log.i(TAG_LOGS, Gson().toJson(data))
}
override fun onFailure(call: Call<List<Event>>, t: Throwable) {
t.printStackTrace()
}
})
}
Mymodel:
data class Event (
val deviceID : Int,
val statusCode : Int,
val accountID : String,
val speedKPH : Int,
.
.
.
}
My composable:
#Composable
fun Greeting(name: String) {
val dataRecox = remember {
mutableStateOf(emptyList<Event>())
}
jsonParsing(dataRecox)
println("======")
println(dataRecox) // ok data
println(dataRecox.value). // ok data
//Uncommenting println(dataRecox.value[0]) I get empty.
//println(dataRecox.value[0])
//Text(text = dataRecox.value[0].uniqueID)
}
When I do not use the information in the console, by calling Greeting("Android") all the data is printed correctly:
The problem comes when I want to use that information:
For example, if I want to print in console println(dataRecox.value[0]) here it returns empty. If I want to use it with a composable Text: Text(text = dataRecox.value[0].uniqueID) it also gives me empty.
Can someone explain to me why this happens, because when I start using the information the data becomes empty.

Answer 1

The way you're doing is totally different of the recommended way... here's my suggestion.
Define a class to represent the screen's state.
data class ScreenState(
val events: List<Event> = emptyList(),
val error: Throwable? = null
)
Use a ViewModel to perform the API request and keep the screen state.
class EventsViewModel : ViewModel()
private val _screenState = MutableStateFlow<ScreenState>(ScreenState())
val screenState = _screenState.asStateFlow()
init {
jsonParsing()
}
fun jsonParsing() {
val TAG_LOGS = "Mariox"
val retrofit = Retrofit.Builder()
.baseUrl("http://myserversample.com/pGet/track/")
.addConverterFactory(GsonConverterFactory.create())
.build()
val retrofitAPI = retrofit.create(APIService1::class.java)
retrofitAPI.getRecolector().enqueue(object : Callback<List<Event>> {
override fun onResponse(
call: Call<List<Event>>,
response: Response<List<Event>>
) {
val data = response.body()
Log.i(TAG_LOGS, Gson().toJson(data))
_screenState.update {
ScreenState(it.events)
}
}
override fun onFailure(call: Call<List<Event>>, t: Throwable) {
t.printStackTrace()
_screenState.update {
ScreenState(error = t)
}
}
})
}
}
Instantiate the ViewModel and use it in your screen...
#Composable
fun Greeting(name: String) {
val vm = viewModel<EventsViewModel>()
val screenState by vm.screenState.observeAsState()
LazyColumn(Modifier.fillMaxSize()) {
items(screenState.items) {
Text(it. accountID)
}
}
}