```enum class ScreenState(val error: ErrorAlertType? = null) { LOADING, ERROR, OK } enum class ...

# android

[Ink]

enum class ScreenState(val error: ErrorAlertType? = null) {
    LOADING, ERROR, OK
}

enum class ErrorAlertType {
    CONNECTION, UNKNOWN
}

and then

val state = ScreenState.ERROR(ErrorAlertType.UNKNOWN)

How I can define my ScreenState to get optional parameter for ERROR state?

[Damian Zawadzki]

Use sealed class instead:

sealed class ScreenState {
object Loading : ScreenState()
data class Error(val error: ErrorAlertType? = null) : ScreenState()
object Ok : ScreenState()
}

enum class ErrorAlertType {
    CONNECTION, UNKNOWN
}

val state = ScreenState.Error(ErrorAlertType.UNKNOWN)

[Grégory Lureau]

Agree with Damian. Just to show the limitation, if you want to use enum there, you've to know there is only 1 instance of each entry in your enum, so you can define your enum like this :

enum class ScreenState(val error: ErrorAlertType? = null) {
    LOADING(ErrorAlertType.CONNECTION),
    ERROR(ErrorAlertType.UNKNOWN),
    OK
}

enum class ErrorAlertType {
    CONNECTION, UNKNOWN
}

But it means you can't have LOADING(UNKNOWN) for example, or else you've to define 2 entries in ScreenState (LOADING_CONNECTION, LOADING_UNKNOWN.